Prepare 0.4.2 release (#48)

This fixes an issue where a union with an int member cannot decode
any value that is out of the Int8 bounds.

Also: make SingleValueDecodingContainer throw `typeMismatch` errors
when the expected type doesn't match.

.circleci/config.pkl

@@ -1,5 +1,5 @@
 // ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -13,7 +13,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 // ===----------------------------------------------------------------------===//
-amends "package://pkg.pkl-lang.org/pkl-project-commons/pkl.impl.circleci@1.0.1#/PklCI.pkl"
+amends "package://pkg.pkl-lang.org/pkl-project-commons/pkl.impl.circleci@1.1.1#/PklCI.pkl"
+
+import "pkl:semver"
 
 local swiftTest = new RunStep {
   name = "swift test"
@@ -23,59 +25,78 @@ local swiftTest = new RunStep {
     """
 }
 
-local pklVersion = "0.25.1"
-local pklBinary = "https://repo1.maven.org/maven2/org/pkl-lang/pkl-cli-linux-amd64/\(pklVersion)/pkl-cli-linux-amd64-\(pklVersion).bin"
+local class PklDistribution {
+  /// The version of this distribution
+  version: String(semver.isValid(this))
 
-local downloadPkl = new RunStep {
-  name = "Downloading pkl"
-  command = """
-    mkdir /tmp/pkl
-    curl -L "\(pklBinary)" > /tmp/pkl/pkl
-    chmod +x /tmp/pkl/pkl
-    echo 'export PKL_EXEC=/tmp/pkl/pkl' >> $BASH_ENV
-    """
+  /// Normalized version for use in task names
+  fixed normalizedVersion: String = version.replaceAll(".", "-")
+
+  /// The URL to download this distribution
+  fixed downloadUrl: String = "https://github.com/apple/pkl/releases/download/\(version)/pkl-linux-amd64"
+
+  fixed downloadRunStep: RunStep = new {
+    name = "Downloading pkl-\(version)"
+    command = """
+      PKL=$(mktemp /tmp/pkl-\(version)-XXXXXX)
+      curl -L "\(downloadUrl)" > $PKL
+      chmod +x $PKL
+      echo "export PKL_EXEC=$PKL" >> $BASH_ENV
+      """
+  }
 }
 
+local pklCurrent: PklDistribution = new {
+  version = "0.27.2"
+}
+
+local pklDistributions: Listing<PklDistribution> = new {
+  new { version = "0.25.3" }
+  pklCurrent
+}
+
+local testJobs = jobs.keys.filter((it) -> it.startsWith("test"))
+
 main {
   jobs {
-    "test"
+    ...testJobs
   }
 }
 
 prb {
   jobs {
-    "test"
+    ...testJobs
   }
 }
 
 release {
   jobs {
-    "test"
+    ...testJobs
     new {
       ["pkl-package"] {
         requires {
-          "test"
+          ...testJobs
         }
       }
     }
     new {
       ["pkl-gen-swift-macos"] {
         requires {
-          "test"
+          ...testJobs
         }
       }
     }
     new {
       ["pkl-gen-swift-linux-amd64"] {
         requires {
-          "test"
+          ...testJobs
         }
       }
     }
     new {
       ["pkl-gen-swift-linux-aarch64"] {
         requires {
-          "test"
+          ...testJobs
         }
       }
     }
@@ -100,22 +121,53 @@ triggerDocsBuild = "release"
 triggerPackageDocsBuild = "release"
 
 jobs {
-  ["test"] {
+  for (distribution in pklDistributions) {
+    ["test-pkl-\(distribution.normalizedVersion)"] {
+      docker {
+        new {
+          image = "swift:5.9-rhel-ubi9"
+        }
+      }
+      resource_class = "xlarge"
+      steps {
+        "checkout"
+        distribution.downloadRunStep
+        swiftTest
+        new RunStep { command = "make circleci-config" }
+        new RunStep { command = "make test-snippets" }
+        new RunStep { command = "make test-pkl" }
+        new RunStep { command = "make generate-fixtures" }
+        new StoreTestResults {
+          path = ".out/test-results/"
+        }
+      }
+    }
+  }
+
+  ["test-license-headers"] {
+    docker {
+      new {
+        image = "ghcr.io/korandoru/hawkeye"
+      }
+    }
+    steps {
+      "checkout"
+      new RunStep {
+        command = "/bin/hawkeye check --fail-if-unknown"
+      }
+    }
+  }
+  
+  ["test-format"] {
     docker {
       new {
         image = "swift:5.9-rhel-ubi9"
       }
     }
-    resource_class = "xlarge"
     steps {
       "checkout"
-      downloadPkl
-      swiftTest
-      new RunStep { command = "make test-snippets" }
-      new RunStep { command = "make test-pkl" }
-      new RunStep { command = "make generate-fixtures" }
-      new StoreTestResults {
-        path = ".out/test-results/"
+      new RunStep {
+        command = "make swiftformat-lint"
       }
     }
   }
@@ -168,7 +220,7 @@ jobs {
     }
     steps {
       "checkout"
-      downloadPkl
+      pklCurrent.downloadRunStep
       new RunStep {
         // TODO remove skip-publish-check after initial release
         command = #"$PKL_EXEC project package --skip-publish-check --output-path out/pkl-package/ codegen/src/"#
@@ -216,7 +268,7 @@ jobs {
             --title "${CIRCLE_TAG}" \
             --target "${CIRCLE_SHA1}" \
             --verify-tag \
-            --notes "Release notes: https://pkl-lang.org/swift/CHANGELOG.html#release-${CIRCLE_TAG}" \
+            --notes "Release notes: https://pkl-lang.org/swift/current/CHANGELOG.html#release-${CIRCLE_TAG}" \
             --repo "${CIRCLE_PROJECT_USERNAME}/${CIRCLE_PROJECT_REPONAME}" \
             out/pkl-gen-swift/*
           """#

.circleci/config.yml

@@ -3,21 +3,23 @@ version: '2.1'
 orbs:
   pr-approval: apple/pr-approval@0.1.0
 jobs:
-  test:
+  test-pkl-0-25-3:
     steps:
     - checkout
     - run:
         command: |-
-          mkdir /tmp/pkl
-          curl -L "https://repo1.maven.org/maven2/org/pkl-lang/pkl-cli-linux-amd64/0.25.1/pkl-cli-linux-amd64-0.25.1.bin" > /tmp/pkl/pkl
-          chmod +x /tmp/pkl/pkl
-          echo 'export PKL_EXEC=/tmp/pkl/pkl' >> $BASH_ENV
-        name: Downloading pkl
+          PKL=$(mktemp /tmp/pkl-0.25.3-XXXXXX)
+          curl -L "https://github.com/apple/pkl/releases/download/0.25.3/pkl-linux-amd64" > $PKL
+          chmod +x $PKL
+          echo "export PKL_EXEC=$PKL" >> $BASH_ENV
+        name: Downloading pkl-0.25.3
     - run:
         command: |-
           mkdir -p .out/test-results/
           swift test -vv --parallel --num-workers 1 --xunit-output .out/test-results/xunit.xml -Xswiftc -warnings-as-errors
         name: swift test
+    - run:
+        command: make circleci-config
     - run:
         command: make test-snippets
     - run:
@@ -29,6 +31,48 @@ jobs:
     resource_class: xlarge
     docker:
     - image: swift:5.9-rhel-ubi9
+  test-pkl-0-27-2:
+    steps:
+    - checkout
+    - run:
+        command: |-
+          PKL=$(mktemp /tmp/pkl-0.27.2-XXXXXX)
+          curl -L "https://github.com/apple/pkl/releases/download/0.27.2/pkl-linux-amd64" > $PKL
+          chmod +x $PKL
+          echo "export PKL_EXEC=$PKL" >> $BASH_ENV
+        name: Downloading pkl-0.27.2
+    - run:
+        command: |-
+          mkdir -p .out/test-results/
+          swift test -vv --parallel --num-workers 1 --xunit-output .out/test-results/xunit.xml -Xswiftc -warnings-as-errors
+        name: swift test
+    - run:
+        command: make circleci-config
+    - run:
+        command: make test-snippets
+    - run:
+        command: make test-pkl
+    - run:
+        command: make generate-fixtures
+    - store_test_results:
+        path: .out/test-results/
+    resource_class: xlarge
+    docker:
+    - image: swift:5.9-rhel-ubi9
+  test-license-headers:
+    steps:
+    - checkout
+    - run:
+        command: /bin/hawkeye check --fail-if-unknown
+    docker:
+    - image: ghcr.io/korandoru/hawkeye
+  test-format:
+    steps:
+    - checkout
+    - run:
+        command: make swiftformat-lint
+    docker:
+    - image: swift:5.9-rhel-ubi9
   pkl-gen-swift-macos:
     steps:
     - checkout
@@ -82,11 +126,11 @@ jobs:
     - checkout
     - run:
         command: |-
-          mkdir /tmp/pkl
-          curl -L "https://repo1.maven.org/maven2/org/pkl-lang/pkl-cli-linux-amd64/0.25.1/pkl-cli-linux-amd64-0.25.1.bin" > /tmp/pkl/pkl
-          chmod +x /tmp/pkl/pkl
-          echo 'export PKL_EXEC=/tmp/pkl/pkl' >> $BASH_ENV
-        name: Downloading pkl
+          PKL=$(mktemp /tmp/pkl-0.27.2-XXXXXX)
+          curl -L "https://github.com/apple/pkl/releases/download/0.27.2/pkl-linux-amd64" > $PKL
+          chmod +x $PKL
+          echo "export PKL_EXEC=$PKL" >> $BASH_ENV
+        name: Downloading pkl-0.27.2
     - run:
         command: $PKL_EXEC project package --skip-publish-check --output-path out/pkl-package/ codegen/src/
     - persist_to_workspace:
@@ -125,7 +169,7 @@ jobs:
             --title "${CIRCLE_TAG}" \
             --target "${CIRCLE_SHA1}" \
             --verify-tag \
-            --notes "Release notes: https://pkl-lang.org/swift/CHANGELOG.html#release-${CIRCLE_TAG}" \
+            --notes "Release notes: https://pkl-lang.org/swift/current/CHANGELOG.html#release-${CIRCLE_TAG}" \
             --repo "${CIRCLE_PROJECT_USERNAME}/${CIRCLE_PROJECT_REPONAME}" \
             out/pkl-gen-swift/*
         name: Do release
@@ -164,24 +208,53 @@ workflows:
         type: approval
     - pr-approval/authenticate:
         context: pkl-pr-approval
-    - test:
+    - test-pkl-0-25-3:
+        requires:
+        - hold
+    - test-pkl-0-27-2:
+        requires:
+        - hold
+    - test-license-headers:
+        requires:
+        - hold
+    - test-format:
         requires:
         - hold
-        - pr-approval/authenticate
     when:
       matches:
         value: << pipeline.git.branch >>
         pattern: ^pull/\d+(/head)?$
   main:
     jobs:
-    - test
+    - test-pkl-0-25-3
+    - test-pkl-0-27-2
+    - test-license-headers
+    - test-format
     when:
       equal:
       - main
       - << pipeline.git.branch >>
   release:
     jobs:
-    - test:
+    - test-pkl-0-25-3:
+        filters:
+          branches:
+            ignore: /.*/
+          tags:
+            only: /^v?\d+\.\d+\.\d+$/
+    - test-pkl-0-27-2:
+        filters:
+          branches:
+            ignore: /.*/
+          tags:
+            only: /^v?\d+\.\d+\.\d+$/
+    - test-license-headers:
+        filters:
+          branches:
+            ignore: /.*/
+          tags:
+            only: /^v?\d+\.\d+\.\d+$/
+    - test-format:
         filters:
           branches:
             ignore: /.*/
@@ -189,7 +262,10 @@ workflows:
             only: /^v?\d+\.\d+\.\d+$/
     - pkl-package:
         requires:
-        - test
+        - test-pkl-0-25-3
+        - test-pkl-0-27-2
+        - test-license-headers
+        - test-format
         filters:
           branches:
             ignore: /.*/
@@ -197,7 +273,10 @@ workflows:
             only: /^v?\d+\.\d+\.\d+$/
     - pkl-gen-swift-macos:
         requires:
-        - test
+        - test-pkl-0-25-3
+        - test-pkl-0-27-2
+        - test-license-headers
+        - test-format
         filters:
           branches:
             ignore: /.*/
@@ -205,7 +284,10 @@ workflows:
             only: /^v?\d+\.\d+\.\d+$/
     - pkl-gen-swift-linux-amd64:
         requires:
-        - test
+        - test-pkl-0-25-3
+        - test-pkl-0-27-2
+        - test-license-headers
+        - test-format
         filters:
           branches:
             ignore: /.*/
@@ -213,7 +295,10 @@ workflows:
             only: /^v?\d+\.\d+\.\d+$/
     - pkl-gen-swift-linux-aarch64:
         requires:
-        - test
+        - test-pkl-0-25-3
+        - test-pkl-0-27-2
+        - test-license-headers
+        - test-format
         filters:
           branches:
             ignore: /.*/

.gitignore

@@ -1,5 +1,6 @@
 .DS_Store
 .build
+.index-build
 /Packages
 /*.xcodeproj
 xcuserdata/
@@ -16,4 +17,5 @@ DerivedData/
 .out/
 out/
 
-.cicd/
+.cicd/
+.pkl-lsp/

.spi.yml

@@ -0,0 +1,4 @@
+version: 1
+builder:
+  configs:
+    - documentation_targets: ['PklSwift']

.swiftformat

@@ -15,9 +15,8 @@
 --guardelse same-line
 --nevertrailing filter
 --extensionacl on-declarations
---header "// ===----------------------------------------------------------------------===//\n// Copyright © {year} Apple Inc. and the Pkl project authors. All rights reserved.\n//\n// Licensed under the Apache License, Version 2.0 (the \"License\");\n// you may not use this file except in compliance with the License.\n// You may obtain a copy of the License at\n//\n//	https://www.apache.org/licenses/LICENSE-2.0\n//\n// Unless required by applicable law or agreed to in writing, software\n// distributed under the License is distributed on an \"AS IS\" BASIS,\n// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n// See the License for the specific language governing permissions and\n// limitations under the License.\n// ===----------------------------------------------------------------------===//"
 
 # rules
 
 --disable spaceAroundOperators
---disable wrapMultilineStatementBraces
+--disable wrapMultilineStatementBraces

DEVELOPMENT.adoc

@@ -0,0 +1,31 @@
+= Development
+
+== Running the formatter
+
+This project uses two formatting tools: https://github.com/korandoru/hawkeye[hawkeye] and https://github.com/nicklockwood/SwiftFormat[SwiftFormat].
+
+To install swiftformat:
+
+[source,shell]
+----
+brew install swiftformat
+----
+
+To install hawkeye locally, you will need to install the https://rustup.rs[Rust toolchain], then run:
+
+[source,shell]
+----
+cargo install hawkeye
+----
+
+To run formatters:
+
+[source,shell]
+----
+make format
+
+# Alternatively, individually:
+swiftformat .
+
+hawkeye format
+----

Makefile

@@ -108,3 +108,19 @@ pkl-gen-swift-release: $(PKL_GEN_SWIFT_RELEASE)
 .PHONY: pkl-gen-swift-release-output
 pkl-gen-swift-release-output:
 	@echo "$(PKL_GEN_SWIFT_RELEASE)" | xargs
+
+.PHONY: circleci-config
+circleci-config:
+	$(PKL_EXEC) eval .circleci/config.pkl -o .circleci/config.yml
+	git diff --exit-code
+
+swiftformat:
+	swift package plugin --allow-writing-to-package-directory swiftformat .
+
+swiftformat-lint:
+	swift package plugin --allow-writing-to-package-directory swiftformat --lint .
+
+license-format: .build/tools/hawkeye
+	.build/tools/hawkeye format
+
+format: swiftformat license-format

Package.resolved

@@ -1,5 +1,14 @@
 {
   "pins" : [
+    {
+      "identity" : "semanticversion",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/SwiftPackageIndex/SemanticVersion",
+      "state" : {
+        "revision" : "ea8eea9d89842a29af1b8e6c7677f1c86e72fa42",
+        "version" : "0.4.0"
+      }
+    },
     {
       "identity" : "swift-argument-parser",
       "kind" : "remoteSourceControl",
@@ -9,6 +18,24 @@
         "version" : "1.2.3"
       }
     },
+    {
+      "identity" : "swift-docc-plugin",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/swiftlang/swift-docc-plugin",
+      "state" : {
+        "revision" : "85e4bb4e1cd62cec64a4b8e769dcefdf0c5b9d64",
+        "version" : "1.4.3"
+      }
+    },
+    {
+      "identity" : "swift-docc-symbolkit",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/swiftlang/swift-docc-symbolkit",
+      "state" : {
+        "revision" : "b45d1f2ed151d057b54504d653e0da5552844e34",
+        "version" : "1.0.0"
+      }
+    },
     {
       "identity" : "swift-system",
       "kind" : "remoteSourceControl",
@@ -17,6 +44,15 @@
         "revision" : "025bcb1165deab2e20d4eaba79967ce73013f496",
         "version" : "1.2.1"
       }
+    },
+    {
+      "identity" : "swiftformat",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/nicklockwood/SwiftFormat",
+      "state" : {
+        "revision" : "468a7d32dedc8d352c191594b3b45d9fd8ba291b",
+        "version" : "0.55.5"
+      }
     }
   ],
   "version" : 2

Package.swift

@@ -1,4 +1,20 @@
 // swift-tools-version: 5.9
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
 import PackageDescription
 
 let package = Package(
@@ -6,7 +22,6 @@ let package = Package(
     platforms: [
         // required because of `Duration` API
         .macOS(.v13),
-        .iOS(.v13),
     ],
     products: [
         .library(
@@ -25,11 +40,16 @@ let package = Package(
     dependencies: [
         .package(url: "https://github.com/apple/swift-system", from: "1.2.1"),
         .package(url: "https://github.com/apple/swift-argument-parser", from: "1.2.3"),
+        .package(url: "https://github.com/SwiftPackageIndex/SemanticVersion", from: "0.4.0"),
+        // to enable `swift package generate-documentation --target PklSwift`
+        .package(url: "https://github.com/swiftlang/swift-docc-plugin", from: "1.1.0"),
+        // to enable `swift package plugin --allow-writing-to-package-directory swiftformat`
+        .package(url: "https://github.com/nicklockwood/SwiftFormat", from: "0.55.0"),
     ],
     targets: [
         .target(
             name: "PklSwift",
-            dependencies: ["MessagePack", "PklSwiftInternals"]
+            dependencies: ["MessagePack", "PklSwiftInternals", "SemanticVersion"]
         ),
         .target(
             name: "PklSwiftInternals"
@@ -48,6 +68,10 @@ let package = Package(
             ],
             resources: [.embedInCode("Resources/VERSION.txt")]
         ),
+        .executableTarget(
+            name: "test-external-reader",
+            dependencies: ["PklSwift"]
+        ),
         .testTarget(
             name: "PklSwiftTests",
             dependencies: [

README.adoc

@@ -8,4 +8,4 @@ The full documentation for this library can be found on our link:https://pkl-lan
 
 To get up and going, reference the link:https://pkl-lang.org/swift/current/quickstart.html[quick start guide].
 
-When upgrading pkl-swift, reference the link:https://pkl-lang.org/pkl/swift/current/CHANGELOG.html[changelog] for details.
+When upgrading pkl-swift, reference the link:https://pkl-lang.org/swift/current/CHANGELOG.html[changelog] for details.

Sources/MessagePack/AnyCodingKey.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 struct AnyCodingKey: CodingKey, Equatable {
     let stringValue: String

Sources/MessagePack/Box.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/Decoder/KeyedDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
@@ -185,7 +185,6 @@ extension MessagePackValue {
         case .ext:
             // TODO: implement this?
             fatalError("Cannot convert \(self) to \(T.self)")
-
         case .timestamp:
             // TODO: implement this?
             fatalError("Cannot convert \(self) to \(T.self)")

Sources/MessagePack/Decoder/KeyedSingleDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/Decoder/MessagePackDecoder.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/Decoder/SingleValueDecodingContainer.swift

@@ -1,22 +1,22 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
-#if os(Linux)
+#if os(Linux) || os(Windows)
 let NSEC_PER_SEC: UInt64 = 1_000_000_000
 #endif
 

Sources/MessagePack/Decoder/UnkeyedDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/Decoder/UnkeyedMapDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/Decoder/_MessagePackDecoder.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/Encoder/KeyedEncodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/Encoder/MessagePackEncoder.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
@@ -44,10 +44,13 @@ public final class MessagePackEncoder {
             try Box<Data>(data).encode(to: encoder)
         case let date as Date:
             try Box<Date>(date).encode(to: encoder)
-        case let bytes as [UInt8]:
-            try Box<[UInt8]>(bytes).encode(to: encoder)
         case let url as URL:
             try Box<URL>(url).encode(to: encoder)
+        case let bytes as [UInt8]:
+            guard type(of: value) == [UInt8].self else {
+                fallthrough
+            }
+            try Box<[UInt8]>(bytes).encode(to: encoder)
         default:
             try value.encode(to: encoder)
         }

Sources/MessagePack/Encoder/SingleValueEncodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
@@ -304,8 +304,6 @@ extension _MessagePackEncoder.SingleValueContainer: SingleValueEncodingContainer
             try self.encode(data)
         case let date as Date:
             try self.encode(date)
-        case let bytes as [UInt8]:
-            try self.encode(bytes)
         case let url as URL:
             try self.encode(url)
         case let bool as Bool:
@@ -334,9 +332,16 @@ extension _MessagePackEncoder.SingleValueContainer: SingleValueEncodingContainer
             try self.encode(uint64)
         case let num as any BinaryInteger & Encodable:
             try self.encode(num)
+        case let bytes as [UInt8]:
+            guard type(of: value) == [UInt8].self else {
+                fallthrough
+            }
+            try self.encode(bytes)
         default:
             let writer: Writer = BufferWriter()
             let encoder = _MessagePackEncoder()
+            encoder.userInfo = userInfo
+            encoder.codingPath = codingPath
             try value.encode(to: encoder)
             try encoder.write(into: writer)
             let data = (writer as! BufferWriter).bytes

Sources/MessagePack/Encoder/UnkeyedEncodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/MessagePack/FixedWidthInteger.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 extension FixedWidthInteger {
     init(bytes: [UInt8]) {

Sources/MessagePack/IO.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 public protocol Writer {
     /// Write the given bytes into an output somewhere.

Sources/PklSwift/API/DataSize.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 import MessagePack

Sources/PklSwift/API/Duration.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/PklSwift/API/Pair.swift

@@ -1,45 +0,0 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//	https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-// ===----------------------------------------------------------------------===//
-
-import Foundation
-
-/// Pair is the Swift representation of Pkl's `pkl.Pair`.
-public struct Pair<A, B>: Hashable where A: Hashable, B: Hashable {
-    public init(_ first: A, _ second: B) {
-        self.first = first
-        self.second = second
-    }
-
-    /// The value of the first component of this ``Pair``.
-    let first: A
-
-    /// The value of the second component of this ``Pair``.
-    let second: B
-}
-
-extension Pair: CustomStringConvertible where A: CustomStringConvertible, B: CustomStringConvertible {
-    public var description: String {
-        "Pair(\(self.first.description), \(self.second.description))"
-    }
-}
-
-extension Pair: Decodable where A: Decodable, B: Decodable {
-    public init(from decoder: Decoder) throws {
-        var partsDecoder = try decoder.unkeyedContainer()
-        self.first = try partsDecoder.decode(A.self)
-        self.second = try partsDecoder.decode(B.self)
-    }
-}

Sources/PklSwift/Decoder/PklDecoder.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 import MessagePack
@@ -205,6 +205,7 @@ extension _PklDecoder {
                         ))
                 }
                 var arr: [AnyHashable?] = []
+                arr.reserveCapacity(pklArray.count)
                 for v in pklArray {
                     try arr.append(self.decodePolymorphic(v, codingPath: codingPath)?.value)
                 }

Sources/PklSwift/Decoder/PklMapDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import MessagePack
 

Sources/PklSwift/Decoder/PklSingleValueDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import MessagePack
 
@@ -37,11 +37,13 @@ class PklSingleValueDecodingContainer: SingleValueDecodingContainer {
         switch self.value {
         case .bool(let value): return value
         default:
-            throw DecodingError.dataCorrupted(
+            throw DecodingError.typeMismatch(
+                Bool.self,
                 .init(
                     codingPath: self.codingPath,
                     debugDescription: "Expected a boolean, but got \(self.value.debugDataTypeDescription)"
-                ))
+                )
+            )
         }
     }
 
@@ -49,11 +51,13 @@ class PklSingleValueDecodingContainer: SingleValueDecodingContainer {
         switch self.value {
         case .string(let value): return value
         default:
-            throw DecodingError.dataCorrupted(
+            throw DecodingError.typeMismatch(
+                String.self,
                 .init(
                     codingPath: self.codingPath,
                     debugDescription: "Expected a string, but got \(self.value.debugDataTypeDescription)"
-                ))
+                )
+            )
         }
     }
 
@@ -61,11 +65,13 @@ class PklSingleValueDecodingContainer: SingleValueDecodingContainer {
         switch self.value {
         case .float(let value): return Double(value)
         default:
-            throw DecodingError.dataCorrupted(
+            throw DecodingError.typeMismatch(
+                Double.self,
                 .init(
                     codingPath: self.codingPath,
                     debugDescription: "Expected a float, but got \(self.value.debugDataTypeDescription)"
-                ))
+                )
+            )
         }
     }
 
@@ -73,11 +79,13 @@ class PklSingleValueDecodingContainer: SingleValueDecodingContainer {
         switch self.value {
         case .float(let value): return Float(value)
         default:
-            throw DecodingError.dataCorrupted(
+            throw DecodingError.typeMismatch(
+                Float.self,
                 .init(
                     codingPath: self.codingPath,
                     debugDescription: "Expected a float, but got \(self.value.debugDataTypeDescription)"
-                ))
+                )
+            )
         }
     }
 
@@ -124,7 +132,7 @@ class PklSingleValueDecodingContainer: SingleValueDecodingContainer {
     func decode<T>(_ type: T.Type) throws -> T where T: Decodable {
         if type == PklAny.self {
             guard let result = try _PklDecoder.decodePolymorphic(value, codingPath: codingPath) else {
-                throw DecodingError.dataCorrupted(.init(codingPath: self.codingPath, debugDescription: "Tried to decode but got nil"))
+                throw DecodingError.typeMismatch(T.self, .init(codingPath: self.codingPath, debugDescription: "Tried to decode but got nil"))
             }
             return result as! T
         }
@@ -135,13 +143,25 @@ class PklSingleValueDecodingContainer: SingleValueDecodingContainer {
 
     private func decodeBinaryInteger<T>() throws -> T where T: BinaryInteger {
         switch self.value {
-        case .int(let value): return T(value)
+        case .int(let value):
+            guard let result = T(exactly: value) else {
+                throw DecodingError.typeMismatch(
+                    T.self,
+                    .init(
+                        codingPath: self.codingPath,
+                        debugDescription: "Cannot fit \(value) into \(String(describing: T.self))"
+                    )
+                )
+            }
+            return result
         default:
-            throw DecodingError.dataCorrupted(
+            throw DecodingError.typeMismatch(
+                T.self,
                 .init(
                     codingPath: self.codingPath,
                     debugDescription: "Expected an int, but got \(self.value.debugDataTypeDescription)"
-                ))
+                )
+            )
         }
     }
 }

Sources/PklSwift/Decoder/PklTypedDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import MessagePack
 

Sources/PklSwift/Decoder/PklUnkeyedDecodingContainer.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import MessagePack
 
@@ -49,11 +49,6 @@ extension _PklDecoder {
                     throw error("Expected an array at slot 2, but got \(value[1].debugDataTypeDescription)")
                 }
                 self.members = members
-            } else if value.count == 3 {
-                guard pklType == .pair else {
-                    throw error("Expected to find a Pair type marker, but found \(pklType)")
-                }
-                self.members = Array(value[1...2])
             } else {
                 throw error("Expected 2 or 3 values, but found \(value.count)")
             }

Sources/PklSwift/Evaluator.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
@@ -36,17 +36,14 @@ public func withEvaluator<T>(_ action: (Evaluator) async throws -> T) async thro
     try await withEvaluator(options: .preconfigured, action)
 }
 
-/// Like ``withProjectEvaluator(projectDir:options:_:)``, but configured with preconfigured otions.
+/// Like ``withProjectEvaluator(projectBaseURI:options:_:)``, but configured with preconfigured options.
 ///
 /// - Parameters:
-///   - projectDir: The directory containing the PklProject file.
+///   - projectBaseURI: The base path containing the PklProject file.
 ///   - action: The action to perform.
 /// - Returns: The result of the action.
-public func withProjectEvaluator<T>(
-    projectDir: String,
-    _ action: (Evaluator) async throws -> T
-) async throws -> T {
-    try await withProjectEvaluator(projectDir: projectDir, options: .preconfigured, action)
+public func withProjectEvaluator<T>(projectBaseURI: URL, _ action: (Evaluator) async throws -> T) async throws -> T {
+    try await withProjectEvaluator(projectBaseURI: projectBaseURI, options: .preconfigured, action)
 }
 
 /// Convenience method for initializing an evaluator from the project.
@@ -56,17 +53,17 @@ public func withProjectEvaluator<T>(
 ///
 /// After `action` completes, the evaluator is closed.
 /// - Parameters:
-///   - projectDir: The directory containing the PklProject file.
+///   - projectBaseURI: The base path containing the PklProject file.
 ///   - options: The base options used to configure the evaluator.
 ///   - action: The action to perform.
 /// - Returns: The result of the action.
 public func withProjectEvaluator<T>(
-    projectDir: String,
+    projectBaseURI: URL,
     options: EvaluatorOptions,
     _ action: (Evaluator) async throws -> T
 ) async throws -> T {
     try await withEvaluatorManager { manager in
-        let evaluator = try await manager.newProjectEvaluator(projectDir: projectDir, options: options)
+        let evaluator = try await manager.newProjectEvaluator(projectBaseURI: projectBaseURI, options: options)
         return try await action(evaluator)
     }
 }

Sources/PklSwift/EvaluatorManager.swift

@@ -1,22 +1,31 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 import MessagePack
+import SemanticVersion
+#if os(Windows)
+import WinSDK.System
 
+let ENV_SEPARATOR=";"
+let PKL_EXEC_NAME="pkl.exe"
+#else
+let ENV_SEPARATOR=":"
+let PKL_EXEC_NAME="pkl"
+#endif
 /// Perfoms `action`, returns its result and then closes the manager.
 ///
 /// - Parameter action: The action to perform
@@ -37,6 +46,47 @@ public func withEvaluatorManager<T>(_ action: (EvaluatorManager) async throws ->
     }
 }
 
+func getenv(_ key: String) -> String? {
+    #if os(Windows)
+    let key = key.lowercased()
+    return ProcessInfo.processInfo.environment.first { (envKey: String, _: String) in
+        key == envKey.lowercased()
+    }?.value
+    #else
+    return ProcessInfo.processInfo.environment[key]
+    #endif
+}
+
+/// Resolve the (CLI) command to invoke Pkl.
+///
+/// First, checks the `PKL_EXEC` environment variable. If that is not set, searches the `PATH` for a directory
+/// containing `pkl`.
+func getPklCommand() throws -> [String] {
+    if let exec = getenv("PKL_EXEC") {
+        return exec.components(separatedBy: " ")
+    }
+    guard let path = getenv("PATH") else {
+        throw PklError("Unable to read PATH environment variable.")
+    }
+    for dir in path.components(separatedBy: ENV_SEPARATOR) {
+        do {
+            let contents = try FileManager.default.contentsOfDirectory(atPath: dir)
+            if let pkl = contents.first(where: { $0 == PKL_EXEC_NAME }) {
+                let file = NSString.path(withComponents: [dir, pkl])
+                if FileManager.default.isExecutableFile(atPath: file) {
+                    return [file]
+                }
+            }
+        } catch {
+            if error._domain == NSCocoaErrorDomain {
+                continue
+            }
+            throw error
+        }
+    }
+    throw PklError("Unable to find `pkl` command on PATH.")
+}
+
 /// Provides handlers for managing the lifecycles of Pkl evaluators. If binding to Pkl as a child process, an evaluator
 /// manager represents a single child process.
 ///
@@ -55,9 +105,11 @@ public actor EvaluatorManager {
 
     var isClosed: Bool = false
 
+    var pklVersion: String?
+
     // note; when our C bindings are released, change `init()` based on compiler flags.
     public init() {
-        self.init(transport: ChildProcessMessageTransport())
+        self.init(transport: ServerMessageTransport())
     }
 
     // Used for testing only.
@@ -72,6 +124,31 @@ public actor EvaluatorManager {
         }
     }
 
+    /// Get the semantic version as a String of the Pkl interpreter being used.
+    func getVersion() throws -> String {
+        if let pklVersion {
+            return pklVersion
+        }
+
+        let pklCommand = try getPklCommand()
+        let process = Process()
+        process.executableURL = URL(fileURLWithPath: pklCommand[0])
+        process.arguments = Array(pklCommand.dropFirst()) + ["--version"]
+        let pipe = Pipe()
+        process.standardOutput = pipe
+        debug("Spawning command \(pklCommand[0]) with arguments \(process.arguments!)")
+        try process.run()
+        guard let outputData = try pipe.fileHandleForReading.readToEnd(),
+              let output = String(data: outputData, encoding: .utf8)?.split(separator: " "),
+              output.count > 2,
+              output[0] == "Pkl" else {
+            throw PklError("Could not get version from Pkl binary")
+        }
+
+        self.pklVersion = String(output[1])
+        return self.pklVersion!
+    }
+
     private func listenForIncomingMessages() async throws {
         for try await message in try self.transport.getMessages() {
             debug("EvaluatorManager got message \(message)")
@@ -127,24 +204,24 @@ public actor EvaluatorManager {
     ///   - options: The options used to configure the evaluator.
     ///   - action: The action to run with the evaluator.
     public func withEvaluator<T>(options: EvaluatorOptions, _ action: (Evaluator) async throws -> T) async throws -> T {
-        let evalautor = try await newEvaluator(options: options)
+        let evaluator = try await newEvaluator(options: options)
         var closed = false
         do {
-            let result = try await action(evalautor)
-            try await evalautor.close()
+            let result = try await action(evaluator)
+            try await evaluator.close()
             closed = true
             return result
         } catch {
             if !closed {
-                try await evalautor.close()
+                try await evaluator.close()
             }
             throw error
         }
     }
 
     /// Convenience method for constructing a project evaluator with preconfigured base options.
-    public func withProjectEvaluator<T>(projectDir: String, _ action: (Evaluator) async throws -> T) async throws -> T {
-        try await self.withProjectEvaluator(projectDir: projectDir, options: .preconfigured, action)
+    public func withProjectEvaluator<T>(projectBaseURI: URL, _ action: (Evaluator) async throws -> T) async throws -> T {
+        try await self.withProjectEvaluator(projectBaseURI: projectBaseURI, options: .preconfigured, action)
     }
 
     /// Constructs an evaluator that is configured by the project within the project dir.
@@ -155,20 +232,20 @@ public actor EvaluatorManager {
     /// After the action completes or throws, the evaluator is closed.
     ///
     /// - Parameters:
-    ///   - projectDir: The project directory that contains the PklProject file.
+    ///   - projectBaseURI: The project base path that contains the PklProject file.
     ///   - options: The options used to configure the evaluator.
     ///   - action: The action to run with the evaluator.
-    public func withProjectEvaluator<T>(projectDir: String, options: EvaluatorOptions, _ action: (Evaluator) async throws -> T) async throws -> T {
-        let evalautor = try await newProjectEvaluator(projectDir: projectDir, options: options)
+    public func withProjectEvaluator<T>(projectBaseURI: URL, options: EvaluatorOptions, _ action: (Evaluator) async throws -> T) async throws -> T {
+        let evaluator = try await newProjectEvaluator(projectBaseURI: projectBaseURI, options: options)
         var closed = false
         do {
-            let result = try await action(evalautor)
-            try await evalautor.close()
+            let result = try await action(evaluator)
+            try await evaluator.close()
             closed = true
             return result
         } catch {
             if !closed {
-                try await evalautor.close()
+                try await evaluator.close()
             }
             throw error
         }
@@ -176,13 +253,21 @@ public actor EvaluatorManager {
 
     /// Creates a new evaluator with the provided options.
     ///
-    /// To create an evaluator that understands project dependencies, use ``newProjectEvaluator(projectDir:options:)``.
+    /// To create an evaluator that understands project dependencies, use
+    /// ``newProjectEvaluator(projectBaseURI:options:)``.
     ///
     /// - Parameter options: The options used to configure the evaluator.
     public func newEvaluator(options: EvaluatorOptions) async throws -> Evaluator {
         if self.isClosed {
             throw PklError("The evaluator manager is closed")
         }
+        let version = try SemanticVersion(getVersion())!
+        guard options.http == nil || version >= pklVersion0_26 else {
+            throw PklError("http options are not supported on Pkl versions lower than 0.26")
+        }
+        guard (options.externalModuleReaders == nil && options.externalResourceReaders == nil) || version >= pklVersion0_27 else {
+            throw PklError("external reader options are not supported on Pkl versions lower than 0.27")
+        }
         let req = options.toMessage()
         guard let response = try await ask(req) as? CreateEvaluatorResponse else {
             throw PklBugError.invalidMessageCode(
@@ -209,15 +294,15 @@ public actor EvaluatorManager {
     //  Any `evaluatorSettings` set within the PklProject file overwrites any fields set on `options`.
     ///
     /// - Parameters:
-    ///   - projectDir: The project directory containing the `PklProject` file.
+    ///   - projectBaseURI: The project base path containing the `PklProject` file.
     ///   - options: The base options used to configure the evaluator.
-    public func newProjectEvaluator(projectDir: String, options: EvaluatorOptions) async throws -> Evaluator {
+    public func newProjectEvaluator(projectBaseURI: URL, options: EvaluatorOptions) async throws -> Evaluator {
         if self.isClosed {
             throw PklError("The evaluator manager is closed")
         }
         return try await self.withEvaluator(options: .preconfigured) { projectEvaluator in
             let project = try await projectEvaluator.evaluateOutputValue(
-                source: .path("\(projectDir)/PklProject"),
+                source: .path("\(projectBaseURI)/PklProject"),
                 asType: Project.self
             )
             return try await self.newEvaluator(options: options.withProject(project))
@@ -287,3 +372,13 @@ enum PklBugError: Error {
     case invalidEvaluatorId(String)
     case unknownMessage(String)
 }
+
+let pklVersion0_25 = SemanticVersion("0.25.0")!
+let pklVersion0_26 = SemanticVersion("0.26.0")!
+let pklVersion0_27 = SemanticVersion("0.27.0")!
+
+let supportedPklVersions = [
+    pklVersion0_25,
+    pklVersion0_26,
+    pklVersion0_27,
+]

Sources/PklSwift/EvaluatorOptions.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
@@ -30,8 +30,11 @@ public struct EvaluatorOptions {
         cacheDir: String? = nil,
         outputFormat: String? = nil,
         logger: Logger = Loggers.noop,
-        projectDir: String? = nil,
-        declaredProjectDependencies: [String: ProjectDependency]? = nil
+        projectBaseURI: URL? = nil,
+        http: Http? = nil,
+        declaredProjectDependencies: [String: ProjectDependency]? = nil,
+        externalModuleReaders: [String: ExternalReader]? = nil,
+        externalResourceReaders: [String: ExternalReader]? = nil
     ) {
         self.allowedModules = allowedModules
         self.allowedResources = allowedResources
@@ -45,8 +48,11 @@ public struct EvaluatorOptions {
         self.cacheDir = cacheDir
         self.outputFormat = outputFormat
         self.logger = logger
-        self.projectDir = projectDir
+        self.projectBaseURI = projectBaseURI
+        self.http = http
         self.declaredProjectDependencies = declaredProjectDependencies
+        self.externalModuleReaders = externalModuleReaders
+        self.externalResourceReaders = externalResourceReaders
     }
 
     /// Regular expression patterns that control what modules are allowed to be imported in a Pkl program.
@@ -106,15 +112,33 @@ public struct EvaluatorOptions {
     /// It is meant to be set by lower level logic in Swift code that first evaluates the PklProject,
     /// which then configures ``EvaluatorOptions`` accordingly.
     ///
-    /// To emulate the CLI's `--project-dir` flag, create an evaluator with ``withProjectEvaluator(projectDir:_:)``,
+    /// To emulate the CLI's `--project-dir` flag, create an evaluator with ``withProjectEvaluator(projectBaseURI:_:)``,
     /// or ``EvaluatorManager/newProjectEvaluator()``.
-    public var projectDir: String?
+    public var projectBaseURI: URL?
 
-    /// The set of dependencies available to modules within ``projectDir``.
+    /// Settings that control how Pkl talks to HTTP(S) servers.
     ///
-    /// When importing dependencies, a `PklProject.deps.json` file must exist within ``projectDir``
+    /// Added in Pkl 0.26.
+    /// These fields are ignored if targeting Pkl 0.25.
+    public var http: Http?
+
+    /// The set of dependencies available to modules within ``projectBaseURI``.
+    ///
+    /// When importing dependencies, a `PklProject.deps.json` file must exist within ``projectBaseURI``
     /// that contains the project's resolved dependencies.
     public var declaredProjectDependencies: [String: ProjectDependency]?
+
+    /// Registered external commands that implement module reader schemes.
+    ///
+    /// Added in Pkl 0.27.
+    /// If the underlying Pkl does not support external readers, evaluation will fail when a registered scheme is used.
+    public var externalModuleReaders: [String: ExternalReader]?
+
+    /// Registered external commands that implement resource reader schemes.
+    ///
+    /// Added in Pkl 0.27.
+    /// If the underlying Pkl does not support external readers, evaluation will fail when a registered scheme is used.
+    public var externalResourceReaders: [String: ExternalReader]?
 }
 
 extension EvaluatorOptions {
@@ -153,18 +177,21 @@ extension EvaluatorOptions {
             rootDir: self.rootDir,
             cacheDir: self.cacheDir,
             outputFormat: self.outputFormat,
-            project: self.project()
+            project: self.project(),
+            http: self.http,
+            externalModuleReaders: self.externalModuleReaders,
+            externalResourceReaders: self.externalResourceReaders
         )
     }
 
     func project() -> ProjectOrDependency? {
-        guard let projectDir else {
+        guard let projectBaseURI else {
             return nil
         }
         return .init(
             packageUri: nil,
             type: "project",
-            projectFileUri: "file://\(projectDir)/PklProject",
+            projectFileUri: "file://\(projectBaseURI)/PklProject",
             checksums: nil,
             dependencies: self.declaredProjectDependenciesToMessage(self.declaredProjectDependencies)
         )
@@ -227,28 +254,17 @@ extension EvaluatorOptions {
     /// Builds options that configures the evaluator with settings set on the project.
     ///
     /// Skips any settings that are nil.
-    public func withProjectEvaluatorSettings(_ evaluatorSettings: Project.EvaluatorSettings) -> EvaluatorOptions {
+    public func withProjectEvaluatorSettings(_ evaluatorSettings: PklEvaluatorSettings) -> EvaluatorOptions {
         var options = self
-        if evaluatorSettings.externalProperties != nil {
-            options.properties = evaluatorSettings.externalProperties
-        }
-        if evaluatorSettings.env != nil {
-            options.env = evaluatorSettings.env
-        }
-        if evaluatorSettings.allowedModules != nil {
-            options.allowedModules = evaluatorSettings.allowedModules
-        }
-        if evaluatorSettings.allowedResources != nil {
-            options.allowedResources = evaluatorSettings.allowedResources
-        }
-        if evaluatorSettings.noCache == true {
-            options.cacheDir = nil
-        } else if evaluatorSettings.moduleCacheDir != nil {
-            options.cacheDir = evaluatorSettings.moduleCacheDir
-        }
-        if evaluatorSettings.rootDir != nil {
-            options.rootDir = evaluatorSettings.rootDir
-        }
+        options.properties = evaluatorSettings.externalProperties ?? self.properties
+        options.env = evaluatorSettings.env ?? self.env
+        options.allowedModules = evaluatorSettings.allowedModules ?? self.allowedModules
+        options.allowedResources = evaluatorSettings.allowedResources ?? self.allowedResources
+        options.cacheDir = evaluatorSettings.noCache != nil ? nil : (evaluatorSettings.moduleCacheDir ?? self.cacheDir)
+        options.rootDir = evaluatorSettings.rootDir ?? self.rootDir
+        options.http = evaluatorSettings.http ?? self.http
+        options.externalModuleReaders = evaluatorSettings.externalModuleReaders ?? options.externalModuleReaders
+        options.externalResourceReaders = evaluatorSettings.externalResourceReaders ?? options.externalResourceReaders
         return options
     }
 
@@ -277,7 +293,8 @@ extension EvaluatorOptions {
     /// Builds options with dependencies from the input project.
     public func withProjectDependencies(_ project: Project) -> EvaluatorOptions {
         var options = self
-        options.projectDir = String(URL(string: project.projectFileUri)!.path.dropLast("/PklProject".count))
+        options.projectBaseURI = URL(string: project.projectFileUri)!
+        options.projectBaseURI?.deleteLastPathComponent()
         options.declaredProjectDependencies = self.projectDependencies(project)
         return options
     }

Sources/PklSwift/ExternalReaderClient.swift

@@ -0,0 +1,208 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import MessagePack
+
+// Example usage:
+// import PklSwift
+// @main
+// struct Main {
+//     static func main() async throws {
+//         let client = ExternalReaderClient(
+//             options: ExternalReaderClientOptions(
+//                 resourceReaders: [MyResourceReader()]
+//             ))
+//         try await client.run()
+//     }
+// }
+
+public struct ExternalReaderClientOptions {
+    /// Reader to receive requests.
+    public var requestReader: Reader = FileHandle.standardInput
+
+    /// Writer to publish responses.
+    public var responseWriter: Writer = FileHandle.standardOutput
+
+    /// Readers that allow reading custom resources in Pkl.
+    public var moduleReaders: [ModuleReader] = []
+
+    /// Readers that allow importing custom modules in Pkl.
+    public var resourceReaders: [ResourceReader] = []
+
+    public init(
+        requestReader: Reader = FileHandle.standardInput,
+        responseWriter: Writer = FileHandle.standardOutput,
+        moduleReaders: [ModuleReader] = [],
+        resourceReaders: [ResourceReader] = []
+    ) {
+        self.requestReader = requestReader
+        self.responseWriter = responseWriter
+        self.moduleReaders = moduleReaders
+        self.resourceReaders = resourceReaders
+    }
+}
+
+public class ExternalReaderClient {
+    private let moduleReaders: [ModuleReader]
+    private let resourceReaders: [ResourceReader]
+    private let transport: MessageTransport
+
+    public init(options: ExternalReaderClientOptions) {
+        self.moduleReaders = options.moduleReaders
+        self.resourceReaders = options.resourceReaders
+        self.transport = ExternalReaderMessageTransport(
+            reader: options.requestReader, writer: options.responseWriter
+        )
+    }
+
+    public func run() async throws {
+        for try await message in try self.transport.getMessages() {
+            switch message {
+            case let message as InitializeModuleReaderRequest:
+                try self.handleInitializeModuleReaderRequest(request: message)
+            case let message as InitializeResourceReaderRequest:
+                try self.handleInitializeResourceReaderRequest(request: message)
+            case let message as ReadModuleRequest:
+                try await self.handleReadModuleRequest(request: message)
+            case let message as ReadResourceRequest:
+                try await self.handleReadResourceRequest(request: message)
+            case let message as ListModulesRequest:
+                try await self.handleListModulesRequest(request: message)
+            case let message as ListResourcesRequest:
+                try await self.handleListResourcesRequest(request: message)
+            case _ as CloseExternalProcess:
+                self.close()
+            default:
+                throw PklBugError.unknownMessage("Got request for unknown message: \(message)")
+            }
+        }
+    }
+
+    public func close() {
+        self.transport.close()
+    }
+
+    func handleInitializeModuleReaderRequest(request: InitializeModuleReaderRequest) throws {
+        var response = InitializeModuleReaderResponse(requestId: request.requestId, spec: nil)
+        guard let reader = moduleReaders.first(where: { $0.scheme == request.scheme }) else {
+            try self.transport.send(response)
+            return
+        }
+        response.spec = reader.toMessage()
+        try self.transport.send(response)
+    }
+
+    func handleInitializeResourceReaderRequest(request: InitializeResourceReaderRequest) throws {
+        var response = InitializeResourceReaderResponse(requestId: request.requestId, spec: nil)
+        guard let reader = resourceReaders.first(where: { $0.scheme == request.scheme }) else {
+            try self.transport.send(response)
+            return
+        }
+        response.spec = reader.toMessage()
+        try self.transport.send(response)
+    }
+
+    func handleReadModuleRequest(request: ReadModuleRequest) async throws {
+        var response = ReadModuleResponse(
+            requestId: request.requestId,
+            evaluatorId: request.evaluatorId,
+            contents: nil,
+            error: nil
+        )
+        guard let reader = moduleReaders.first(where: { $0.scheme == request.uri.scheme }) else {
+            response.error = "No module reader found for scheme \(request.uri.scheme!)"
+            try self.transport.send(response)
+            return
+        }
+        do {
+            let result = try await reader.read(url: request.uri)
+            response.contents = result
+            try self.transport.send(response)
+        } catch {
+            response.error = "\(error)"
+            try self.transport.send(response)
+        }
+    }
+
+    func handleReadResourceRequest(request: ReadResourceRequest) async throws {
+        var response = ReadResourceResponse(
+            requestId: request.requestId,
+            evaluatorId: request.evaluatorId,
+            contents: nil,
+            error: nil
+        )
+        guard
+            let reader = resourceReaders.first(where: { $0.scheme == request.uri.scheme }) else {
+            response.error = "No resource reader found for scheme \(request.uri.scheme!)"
+            try self.transport.send(response)
+            return
+        }
+        do {
+            let result = try await reader.read(url: request.uri)
+            response.contents = result
+            try self.transport.send(response)
+        } catch {
+            response.error = "\(error)"
+            try self.transport.send(response)
+        }
+    }
+
+    func handleListModulesRequest(request: ListModulesRequest) async throws {
+        var response = ListModulesResponse(
+            requestId: request.requestId,
+            evaluatorId: request.evaluatorId,
+            pathElements: nil,
+            error: nil
+        )
+        guard let reader = moduleReaders.first(where: { $0.scheme == request.uri.scheme }) else {
+            response.error = "No module reader found for scheme \(request.uri.scheme!)"
+            try self.transport.send(response)
+            return
+        }
+        do {
+            let elems = try await reader.listElements(uri: request.uri)
+            response.pathElements = elems.map { $0.toMessage() }
+            try self.transport.send(response)
+        } catch {
+            response.error = "\(error)"
+            try self.transport.send(response)
+        }
+    }
+
+    func handleListResourcesRequest(request: ListResourcesRequest) async throws {
+        var response = ListResourcesResponse(
+            requestId: request.requestId,
+            evaluatorId: request.evaluatorId,
+            pathElements: nil,
+            error: nil
+        )
+        guard
+            let reader = resourceReaders.first(where: { $0.scheme == request.uri.scheme }) else {
+            response.error = "No resource reader found for scheme \(request.uri.scheme!)"
+            try self.transport.send(response)
+            return
+        }
+        do {
+            let elems = try await reader.listElements(uri: request.uri)
+            response.pathElements = elems.map { $0.toMessage() }
+            try self.transport.send(response)
+        } catch {
+            response.error = "\(error)"
+            try self.transport.send(response)
+        }
+    }
+}

Sources/PklSwift/Logger.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 import MessagePack

Sources/PklSwift/Message.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 import MessagePack
@@ -62,8 +62,8 @@ enum MessageType: Int, Codable {
     case CREATE_EVALUATOR_REQUEST = 0x20
     case CREATE_EVALUATOR_RESPONSE = 0x21
     case CLOSE_EVALUATOR = 0x22
-    case EVALUATOR_REQUEST = 0x23
-    case EVALUATOR_RESPOSNE = 0x24
+    case EVALUATE_REQUEST = 0x23
+    case EVALUATE_RESPONSE = 0x24
     case LOG_MESSAGE = 0x25
     case READ_RESOURCE_REQUEST = 0x26
     case READ_RESOURCE_RESPONSE = 0x27
@@ -73,6 +73,11 @@ enum MessageType: Int, Codable {
     case LIST_RESOURCES_RESPONSE = 0x2B
     case LIST_MODULES_REQUEST = 0x2C
     case LIST_MODULES_RESPONSE = 0x2D
+    case INITIALIZE_MODULE_READER_REQUEST = 0x2E
+    case INITIALIZE_MODULE_READER_RESPONSE = 0x2F
+    case INITIALIZE_RESOURCE_READER_REQUEST = 0x30
+    case INITIALIZE_RESOURCE_READER_RESPONSE = 0x31
+    case CLOSE_EXTERNAL_PROCESS = 0x32
 }
 
 extension MessageType {
@@ -85,9 +90,9 @@ extension MessageType {
         case is CloseEvaluatorRequest:
             return MessageType.CLOSE_EVALUATOR
         case is EvaluateRequest:
-            return MessageType.EVALUATOR_REQUEST
+            return MessageType.EVALUATE_REQUEST
         case is EvaluateResponse:
-            return MessageType.EVALUATOR_RESPOSNE
+            return MessageType.EVALUATE_RESPONSE
         case is LogMessage:
             return MessageType.LOG_MESSAGE
         case is ListResourcesRequest:
@@ -102,6 +107,16 @@ extension MessageType {
             return MessageType.READ_MODULE_RESPONSE
         case is ReadResourceResponse:
             return MessageType.READ_RESOURCE_RESPONSE
+        case is InitializeModuleReaderRequest:
+            return MessageType.INITIALIZE_MODULE_READER_REQUEST
+        case is InitializeModuleReaderResponse:
+            return MessageType.INITIALIZE_MODULE_READER_RESPONSE
+        case is InitializeResourceReaderRequest:
+            return MessageType.INITIALIZE_RESOURCE_READER_REQUEST
+        case is InitializeResourceReaderResponse:
+            return MessageType.INITIALIZE_RESOURCE_READER_RESPONSE
+        case is CloseExternalProcess:
+            return MessageType.CLOSE_EXTERNAL_PROCESS
         default:
             preconditionFailure("Unreachable code")
         }
@@ -122,6 +137,9 @@ struct CreateEvaluatorRequest: ClientRequestMessage {
     var cacheDir: String?
     var outputFormat: String?
     var project: ProjectOrDependency?
+    var http: Http?
+    var externalModuleReaders: [String: ExternalReader]?
+    var externalResourceReaders: [String: ExternalReader]?
 }
 
 struct ProjectOrDependency: Codable {
@@ -230,3 +248,25 @@ struct LogMessage: ServerOneWayMessage {
     // NOTE: not guaranteed to conform to URL. This might have been transformed by a stack frame transformer.
     let frameUri: String
 }
+
+struct InitializeModuleReaderRequest: ServerRequestMessage {
+    var requestId: Int64
+    let scheme: String
+}
+
+struct InitializeModuleReaderResponse: ClientResponseMessage {
+    var requestId: Int64
+    var spec: ModuleReaderSpec?
+}
+
+struct InitializeResourceReaderRequest: ServerRequestMessage {
+    var requestId: Int64
+    let scheme: String
+}
+
+struct InitializeResourceReaderResponse: ClientResponseMessage {
+    var requestId: Int64
+    var spec: ResourceReaderSpec?
+}
+
+struct CloseExternalProcess: ServerOneWayMessage {}

Sources/PklSwift/MessageTransport.swift

@@ -1,21 +1,22 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 import MessagePack
+import SemanticVersion
 
 protocol MessageTransport {
     /// Send a message to the Pkl server.
@@ -30,35 +31,104 @@ protocol MessageTransport {
 
 extension Pipe: Reader {
     public func read(into: UnsafeMutableRawBufferPointer) throws -> Int {
-        let data = try fileHandleForReading.read(upToCount: into.count)
-        if data == nil {
-            return 0
-        }
-        data!.copyBytes(to: into)
-        return data!.count
+        try fileHandleForReading.read(into: into)
     }
 
     public func close() throws {
-        fileHandleForReading.closeFile()
+        try fileHandleForReading.close()
+    }
+}
+
+extension FileHandle: Reader {
+    public func read(into: UnsafeMutableRawBufferPointer) throws -> Int {
+        guard let data = try read(upToCount: into.count) else { return 0 }
+        data.copyBytes(to: into)
+        return data.count
+    }
+
+    public func close() throws {
+        closeFile()
     }
 }
 
 extension Pipe: Writer {
     public func write(_ buffer: UnsafeRawBufferPointer) throws {
-        try fileHandleForWriting.write(contentsOf: buffer)
+        try fileHandleForWriting.write(buffer)
+    }
+}
+
+extension FileHandle: Writer {
+    public func write(_ buffer: UnsafeRawBufferPointer) throws {
+        try self.write(contentsOf: buffer)
+    }
+}
+
+/// A ``MessageTransport`` base class that implements core message handling logic
+public class BaseMessageTransport: MessageTransport {
+    var reader: Reader!
+    var writer: Writer!
+    var encoder: MessagePackEncoder!
+    var decoder: MessagePackDecoder!
+
+    var running: Bool { true }
+
+    func send(_ message: ClientMessage) throws {
+        debug("Sending message: \(message)")
+
+        let messageType = MessageType.getMessageType(message)
+        try self.encoder.encodeArrayHeader(2)
+        try self.encoder.encode(messageType)
+        try self.encoder.encode(message)
+    }
+
+    fileprivate func decodeMessage(_ messageType: MessageType) throws -> ServerMessage {
+        switch messageType {
+        case MessageType.READ_MODULE_REQUEST:
+            return try self.decoder.decode(as: ReadModuleRequest.self)
+        case MessageType.READ_RESOURCE_REQUEST:
+            return try self.decoder.decode(as: ReadResourceRequest.self)
+        case MessageType.LIST_MODULES_REQUEST:
+            return try self.decoder.decode(as: ListModulesRequest.self)
+        case MessageType.LIST_RESOURCES_REQUEST:
+            return try self.decoder.decode(as: ListResourcesRequest.self)
+        default:
+            throw PklBugError.unknownMessage("Received unexpected message: \(messageType)")
+        }
+    }
+
+    func close() {}
+
+    func getMessages() throws -> AsyncThrowingStream<ServerMessage, Error> {
+        AsyncThrowingStream { continuation in
+            Task {
+                while self.running {
+                    do {
+                        let arrayLength = try decoder.decodeArrayLength()
+                        assert(arrayLength == 2)
+                        let code = try decoder.decode(as: MessageType.self)
+                        let message = try decodeMessage(code)
+                        debug("Received message: \(message)")
+                        continuation.yield(message)
+                    } catch {
+                        if self.running {
+                            continuation.finish(throwing: error)
+                        }
+                    }
+                }
+                continuation.finish()
+            }
+        }
     }
 }
 
 /// A ``MessageTransport`` that sends and receives messages by spawning Pkl as a child process.
-public class ChildProcessMessageTransport: MessageTransport {
-    var reader: Pipe!
-    var writer: Pipe!
-    var encoder: MessagePackEncoder!
-    var decoder: MessagePackDecoder!
+public class ServerMessageTransport: BaseMessageTransport {
     var process: Process?
     let pklCommand: [String]?
 
-    convenience init() {
+    override var running: Bool { self.process?.isRunning == true }
+
+    override convenience init() {
         self.init(pklCommand: nil)
     }
 
@@ -66,32 +136,6 @@ public class ChildProcessMessageTransport: MessageTransport {
         self.pklCommand = pklCommand
     }
 
-    private func getPklCommand() throws -> [String] {
-        if let exec = ProcessInfo.processInfo.environment["PKL_EXEC"] {
-            return exec.components(separatedBy: " ")
-        }
-        guard let path = ProcessInfo.processInfo.environment["PATH"] else {
-            throw PklError("Unable to find `pkl` command on PATH.")
-        }
-        for dir in path.components(separatedBy: ":") {
-            do {
-                let contents = try FileManager.default.contentsOfDirectory(atPath: dir)
-                if let pkl = contents.first(where: { $0 == "pkl" }) {
-                    let file = NSString.path(withComponents: [dir, pkl])
-                    if FileManager.default.isExecutableFile(atPath: file) {
-                        return [file]
-                    }
-                }
-            } catch {
-                if error._domain == NSCocoaErrorDomain {
-                    continue
-                }
-                throw error
-            }
-        }
-        throw PklError("Unable to find `pkl` command on PATH.")
-    }
-
     private func ensureProcessStarted() throws {
         if self.process?.isRunning == true { return }
         let pklCommand = try getPklCommand()
@@ -100,8 +144,8 @@ public class ChildProcessMessageTransport: MessageTransport {
         var arguments = Array(pklCommand.dropFirst())
         arguments.append("server")
         self.process!.arguments = arguments
-        self.reader = .init()
-        self.writer = .init()
+        self.reader = Pipe()
+        self.writer = Pipe()
         self.encoder = .init(writer: self.writer)
         self.decoder = .init(reader: self.reader)
         self.process!.standardOutput = self.reader
@@ -110,17 +154,25 @@ public class ChildProcessMessageTransport: MessageTransport {
         try self.process!.run()
     }
 
-    func send(_ message: ClientMessage) throws {
+    override func send(_ message: ClientMessage) throws {
         try self.ensureProcessStarted()
-        debug("Sending message: \(message)")
-
-        let messageType = MessageType.getMessageType(message)
-        try self.encoder.encodeArrayHeader(2)
-        try self.encoder.encode(messageType)
-        try self.encoder.encode(message)
+        try super.send(message)
     }
 
-    func close() {
+    override fileprivate func decodeMessage(_ messageType: MessageType) throws -> ServerMessage {
+        switch messageType {
+        case MessageType.CREATE_EVALUATOR_RESPONSE:
+            return try self.decoder.decode(as: CreateEvaluatorResponse.self)
+        case MessageType.EVALUATE_RESPONSE:
+            return try self.decoder.decode(as: EvaluateResponse.self)
+        case MessageType.LOG_MESSAGE:
+            return try self.decoder.decode(as: LogMessage.self)
+        default:
+            return try super.decodeMessage(messageType)
+        }
+    }
+
+    override func close() {
         if self.process == nil {
             return
         }
@@ -136,45 +188,38 @@ public class ChildProcessMessageTransport: MessageTransport {
         self.process = nil
     }
 
-    private func decodeMessage(_ messageType: MessageType) throws -> ServerMessage {
+    override func getMessages() throws -> AsyncThrowingStream<ServerMessage, Error> {
+        try self.ensureProcessStarted()
+        return try super.getMessages()
+    }
+}
+
+public class ExternalReaderMessageTransport: BaseMessageTransport {
+    override var running: Bool { self._running }
+    private var _running = true
+
+    init(reader: Reader, writer: Writer) {
+        super.init()
+        self.reader = reader
+        self.writer = writer
+        self.encoder = .init(writer: self.writer)
+        self.decoder = .init(reader: self.reader)
+    }
+
+    override fileprivate func decodeMessage(_ messageType: MessageType) throws -> ServerMessage {
         switch messageType {
-        case MessageType.CREATE_EVALUATOR_RESPONSE:
-            return try self.decoder.decode(as: CreateEvaluatorResponse.self)
-        case MessageType.EVALUATOR_RESPOSNE:
-            return try self.decoder.decode(as: EvaluateResponse.self)
-        case MessageType.READ_MODULE_REQUEST:
-            return try self.decoder.decode(as: ReadModuleRequest.self)
-        case MessageType.LOG_MESSAGE:
-            return try self.decoder.decode(as: LogMessage.self)
-        case MessageType.READ_RESOURCE_REQUEST:
-            return try self.decoder.decode(as: ReadResourceRequest.self)
-        case MessageType.LIST_MODULES_REQUEST:
-            return try self.decoder.decode(as: ListModulesRequest.self)
-        case MessageType.LIST_RESOURCES_REQUEST:
-            return try self.decoder.decode(as: ListResourcesRequest.self)
+        case MessageType.INITIALIZE_MODULE_READER_REQUEST:
+            return try self.decoder.decode(as: InitializeModuleReaderRequest.self)
+        case MessageType.INITIALIZE_RESOURCE_READER_REQUEST:
+            return try self.decoder.decode(as: InitializeResourceReaderRequest.self)
+        case MessageType.CLOSE_EXTERNAL_PROCESS:
+            return try self.decoder.decode(as: CloseExternalProcess.self)
         default:
-            fatalError("Unreachable code")
+            return try super.decodeMessage(messageType)
         }
     }
 
-    func getMessages() throws -> AsyncThrowingStream<ServerMessage, Error> {
-        try self.ensureProcessStarted()
-        return AsyncThrowingStream { continuation in
-            Task {
-                while self.process?.isRunning == true {
-                    do {
-                        let arrayLength = try decoder.decodeArrayLength()
-                        assert(arrayLength == 2)
-                        let code = try decoder.decode(as: MessageType.self)
-                        let message = try decodeMessage(code)
-                        debug("Received message: \(message)")
-                        continuation.yield(message)
-                    } catch {
-                        continuation.finish(throwing: error)
-                    }
-                }
-                continuation.finish()
-            }
-        }
+    override func close() {
+        self._running = false
     }
 }

Sources/PklSwift/ModuleSource.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
@@ -36,7 +36,7 @@ extension ModuleSource {
     /// - Parameter path: The file path component.
     public static func path(_ path: String) -> ModuleSource {
         let path = resolvePaths(path)
-        return ModuleSource(uri: URL(string: "file://\(path)")!, text: nil)
+        return ModuleSource(uri: URL(fileURLWithPath: path), text: nil)
     }
 
     /// Creates a synthetic ``ModuleSource`` with the given text.

Sources/PklSwift/PklCodingKey.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 

Sources/PklSwift/PklEvaluatorSettings.swift

@@ -0,0 +1,114 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+/// The Swift representation of standard library module `pkl.EvaluatorSettings`.
+public struct PklEvaluatorSettings: Decodable, Hashable {
+    let externalProperties: [String: String]?
+    let env: [String: String]?
+    let allowedModules: [String]?
+    let allowedResources: [String]?
+    let noCache: Bool?
+    let modulePath: [String]?
+    let timeout: Duration?
+    let moduleCacheDir: String?
+    let rootDir: String?
+    let http: Http?
+
+    /// Added in Pkl 0.27
+    let externalModuleReaders: [String: ExternalReader]?
+
+    /// Added in Pkl 0.27
+    let externalResourceReaders: [String: ExternalReader]?
+
+    /// Whether to format messages and test results with ANSI color colors.
+    ///
+    /// Added in Pkl 0.27
+    let color: PklEvaluatorSettingsColor?
+}
+
+public enum PklEvaluatorSettingsColor: String, CaseIterable, Decodable, Hashable {
+    /// Never format.
+    case never
+
+    /// Format if the process' stdin, stdout, or stderr are connected to a console.
+    case auto
+
+    /// Always format.
+    case always
+}
+
+/// Settings that control how Pkl talks to HTTP(S) servers.
+public struct Http: Codable, Hashable {
+    /// PEM format certificates to trust when making HTTP requests.
+    ///
+    /// If empty, Pkl will trust its own built-in certificates.
+    var caCertificates: [UInt8]?
+
+    /// Configuration of the HTTP proxy to use.
+    ///
+    /// If `nil`, uses the operating system's proxy configuration.
+    /// Configuration of the HTTP proxy to use.
+    var proxy: Proxy?
+}
+
+/// Settings that control how Pkl talks to HTTP proxies.
+public struct Proxy: Codable, Hashable {
+    /// The proxy to use for HTTP(S) connections.
+    ///
+    /// Only HTTP proxies are supported.
+    /// The address must start with `"http://"`, and cannot contain anything other than a host and an optional port.
+    ///
+    /// Example:
+    /// ```
+    /// "http://my.proxy.example.com:5080"
+    /// ```
+    var address: String?
+
+    /// Hosts to which all connections should bypass a proxy.
+    ///
+    ///
+    /// Values can be either hostnames, or IP addresses.
+    /// IP addresses can optionally be provided using
+    /// [CIDR notation](https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing#CIDR_notation).
+    ///
+    /// The value `"*"` is a wildcard that disables proxying for all hosts.
+    ///
+    /// A hostname matches all subdomains.
+    /// For example, `example.com` matches `foo.example.com`, but not `fooexample.com`.
+    /// A hostname that is prefixed with a dot matches the hostname itself,
+    /// so `.example.com` matches `example.com`.
+    ///
+    /// Hostnames do not match their resolved IP addresses.
+    /// For example, the hostname `localhost` will not match `127.0.0.1`.
+    ///
+    /// Optionally, a port can be specified.
+    /// If a port is omitted, all ports are matched.
+    ///
+    /// Example:
+    ///
+    /// ```
+    /// [ "127.0.0.1",
+    ///   "169.254.0.0/16",
+    ///   "example.com",
+    ///   "localhost:5050" ]
+    /// ```
+    var noProxy: [String]?
+}
+
+public struct ExternalReader: Codable, Hashable {
+    var executable: String
+    var arguments: [String]? = nil
+}

Sources/PklSwift/Project.swift

@@ -1,28 +1,26 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
-
-import Foundation
+//===----------------------------------------------------------------------===//
 
 /// The Swift representation of `pkl.Project`
 public struct Project: PklRegisteredType, Hashable, DependencyDeclaredInProjectFile {
-    public static var registeredIdentifier: String = "pkl.Project"
+    public static let registeredIdentifier: String = "pkl.Project"
 
     let package: Package?
 
-    let evaluatorSettings: Project.EvaluatorSettings
+    let evaluatorSettings: PklEvaluatorSettings
 
     let projectFileUri: String
 
@@ -52,7 +50,7 @@ extension Project: Decodable {
     public init(from decoder: Decoder) throws {
         let dec = try decoder.container(keyedBy: PklCodingKey.self)
         let package = try dec.decode(Package?.self, forKey: PklCodingKey(stringValue: "package")!)
-        let evaluatorSettings = try dec.decode(EvaluatorSettings.self, forKey: PklCodingKey(stringValue: "evaluatorSettings")!)
+        let evaluatorSettings = try dec.decode(PklEvaluatorSettings.self, forKey: PklCodingKey(stringValue: "evaluatorSettings")!)
         let projectFileUri = try dec.decode(String.self, forKey: PklCodingKey(stringValue: "projectFileUri")!)
         let tests = try dec.decode([String].self, forKey: PklCodingKey(stringValue: "tests")!)
         let dependencies = try dec.decode([String: PklAny].self, forKey: PklCodingKey(stringValue: "dependencies")!)
@@ -70,7 +68,7 @@ extension Project: Decodable {
 extension Project {
     /// The Swift representation of `pkl.Project#RemoteDependency`
     public struct RemoteDependency: PklRegisteredType, DependencyDeclaredInProjectFile, Decodable, Hashable {
-        public static var registeredIdentifier: String = "pkl.Project#RemoteDependency"
+        public static let registeredIdentifier: String = "pkl.Project#RemoteDependency"
 
         let uri: String
         let checksums: Checksums?
@@ -78,7 +76,7 @@ extension Project {
 
     /// The Swift representation of `pkl.Project#Package`
     public struct Package: PklRegisteredType, Hashable {
-        public static var registeredIdentifier: String = "pkl.Project#Package"
+        public static let registeredIdentifier: String = "pkl.Project#Package"
 
         let name: String
         let baseUri: String
@@ -98,16 +96,11 @@ extension Project {
         let uri: String
     }
 
-    /// The Swift representation of `pkl.Project#EvaluatorSettings
-    public struct EvaluatorSettings: Decodable, Hashable {
-        let externalProperties: [String: String]?
-        let env: [String: String]?
-        let allowedModules: [String]?
-        let allowedResources: [String]?
-        let noCache: Bool?
-        let modulePath: [String]?
-        let timeout: Duration?
-        let moduleCacheDir: String?
-        let rootDir: String?
-    }
+    @available(
+        *,
+        deprecated,
+        message: "Replaced by PklEvaluatorSettings, independent of Project",
+        renamed: "PklEvaluatorSettings"
+    )
+    public typealias EvaluatorSettings = PklEvaluatorSettings
 }

Sources/PklSwift/Reader.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 
@@ -35,8 +35,8 @@ public protocol BaseReader {
     /// birds:catalog/swallow.pkl
     /// ```
     ///
-    /// The first URI conveys name "fred.pkl" within parent "/persons/". The second URI
-    /// conveys the name "persons/fred.pkl" with no hierarchical meaning.
+    /// The first URI conveys name "swallow.pkl" within parent "/catalog/". The second URI
+    /// conveys the name "catalog/swallow.pkl" with no hierarchical meaning.
     var hasHierarchicalUris: Bool { get }
 
     /// Returns elements at a specified path.
@@ -107,6 +107,11 @@ public struct PathElement {
 
     /// Whether the element is a directory or not.
     public let isDirectory: Bool
+
+    public init(name: String, isDirectory: Bool) {
+        self.name = name
+        self.isDirectory = isDirectory
+    }
 }
 
 extension PathElement {

Sources/PklSwift/TypeRegistry.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import MessagePack
 import PklSwiftInternals

Sources/PklSwift/Utils.swift

@@ -1,25 +1,20 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
-#if os(Linux)
-import Glibc
-#else
-import Darwin.C
-#endif
 
 let pklDebug = ProcessInfo.processInfo.environment["PKL_DEBUG"]
 
@@ -80,7 +75,7 @@ public func mapEquals<K>(map1: [K: any DynamicallyEquatable], map2: [K: any Dyna
 public func resolvePaths(_ paths: String...) -> String {
     var result = FileManager.default.currentDirectoryPath
     for path in paths {
-        if path.starts(with: "/") {
+        if path.starts(with: "/") || URL(fileURLWithPath: path).path == path {
             result = path
         } else {
             result = NSString.path(withComponents: [result, path])
@@ -90,3 +85,12 @@ public func resolvePaths(_ paths: String...) -> String {
 }
 
 public let absoluteUriRegex = try! Regex("\\w+:")
+
+public func tempDir() throws -> URL {
+    try (FileManager.default.url(for: .itemReplacementDirectory, in: .userDomainMask, appropriateFor: URL(fileURLWithPath: "/"), create: true))
+}
+
+public func tempFile(suffix: String) throws -> URL {
+    let fileName = ProcessInfo.processInfo.globallyUniqueString + suffix
+    return try (tempDir()).appendingPathComponent(fileName)
+}

Sources/PklSwift/locks.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 //===----------------------------------------------------------------------===//
 //

Sources/PklSwiftInternals/Discovery.cpp

@@ -1,12 +1,18 @@
-//
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2024 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
-//
+/*
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 
 #include "Discovery.h"
 

Sources/PklSwiftInternals/include/Defines.h

@@ -1,12 +1,18 @@
-//
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2024 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
-//
+/*
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 
 #if !defined(PKLS_DEFINES_H)
 #define PKLS_DEFINES_H

Sources/PklSwiftInternals/include/Discovery.h

@@ -1,12 +1,18 @@
-//
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2024 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
-//
+/*
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 
 #if !defined(PKLS_DISCOVERY_H)
 #define PKLS_DISCOVERY_H

Sources/pkl-gen-swift/Generated/GeneratorSettings.pkl.swift

@@ -6,7 +6,7 @@ public enum GeneratorSettings {}
 extension GeneratorSettings {
   /// Settings used to configure code generation.
   public struct Module: PklRegisteredType, Decodable, Hashable {
-    public static var registeredIdentifier: String = "pkl.swift.GeneratorSettings"
+    public static let registeredIdentifier: String = "pkl.swift.GeneratorSettings"
 
     /// The set of modules to turn into Swift code.
     ///

Sources/pkl-gen-swift/PklGenSwift.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import ArgumentParser
 import Foundation
@@ -77,11 +77,6 @@ struct PklGenSwift: AsyncParsableCommand {
     )
     var pklInputModules: [String] = []
 
-    func tempFile() -> URL {
-        let fileName = ProcessInfo.processInfo.globallyUniqueString + ".pkl"
-        return URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(fileName)
-    }
-
     private func generateScriptUrl() -> String {
         if let generateScript = self.generateScript {
             return URL(fileURLWithPath: generateScript).path

Sources/pkl-gen-swift/PklSwiftGenerator.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import Foundation
 import PklSwift
@@ -41,11 +41,6 @@ public struct PklSwiftGenerator {
         }
     }
 
-    private func tempFile() -> URL {
-        let fileName = ProcessInfo.processInfo.globallyUniqueString + ".pkl"
-        return URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(fileName)
-    }
-
     private mutating func runModule(evaluator: Evaluator, pklInputModule: String) async throws {
         let out = resolvePaths(self.settings.outputPath ?? ".out")
         let moduleToEvaluate = """
@@ -55,7 +50,7 @@ public struct PklSwiftGenerator {
 
         moduleToGenerate = theModule
         """
-        let tempFile = tempFile()
+        let tempFile = try tempFile(suffix: ".pkl")
         try moduleToEvaluate.write(to: tempFile, atomically: true, encoding: .utf8)
         let files = try await evaluator.evaluateOutputFiles(source: .url(tempFile))
         for (filename, contents) in files {

Sources/test-external-reader/TestExternalReader.swift

@@ -0,0 +1,51 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import PklSwift
+
+@main
+struct TestExternalReader {
+    static func main() async throws {
+        let client = ExternalReaderClient(
+            options: ExternalReaderClientOptions(
+                resourceReaders: [FibReader()]
+            ))
+        try await client.run()
+    }
+}
+
+struct FibReader: ResourceReader {
+    var scheme: String { "fib" }
+    var isGlobbable: Bool { false }
+    var hasHierarchicalUris: Bool { false }
+    func listElements(uri: URL) async throws -> [PathElement] { throw PklError("not implemented") }
+    func read(url: URL) async throws -> [UInt8] {
+        let key = url.absoluteString.dropFirst(self.scheme.count + 1)
+        guard let n = Int(key), n > 0 else {
+            throw PklError("input uri must be in format fib:<positive integer>")
+        }
+        return Array(String(fibonacci(n: n)).utf8)
+    }
+}
+
+func fibonacci(n: Int) -> Int {
+    var (a, b) = (0, 1)
+    for _ in 0..<n {
+        (a, b) = (b, a + b)
+    }
+    return a
+}

Tests/MessagePackTests/MessagePackDecodingTests.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import XCTest
 

Tests/MessagePackTests/MessagePackEncodingTests.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import XCTest
 

Tests/PklSwiftTests/API/DataSizeTests.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import XCTest
 

Tests/PklSwiftTests/API/DurationTests.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import PklSwift
 import XCTest

Tests/PklSwiftTests/Decoder/PklDecoderTest.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import XCTest
 
@@ -43,6 +43,11 @@ final class PklDecoderTests: XCTestCase {
         XCTAssertEqual(value, 42)
     }
 
+    func testDecodeInt8Overflow() throws {
+        let bytes: [UInt8] = [0xD2, 0xFF, 0x00, 0x00, 0x00]
+        XCTAssertThrowsError(try PklDecoder.decode(Int8.self, from: bytes), "Cannot fit -16777216 into Int8")
+    }
+
     func testDecodeString() throws {
         let bytes: [UInt8] = [
             0xD9, 0x27, 0x74, 0x68, 0x65, 0x20, 0x71, 0x75, 0x69, 0x63, 0x6B, 0x20, 0x66, 0x6F, 0x78,

Tests/PklSwiftTests/EvaluatorManagerTest.swift

@@ -1,20 +1,20 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
-import Foundation
+import SemanticVersion
 import XCTest
 
 @testable import PklSwift
@@ -55,10 +55,10 @@ class EvaluatorManagerTest: XCTestCase {
         let manager1 = EvaluatorManager()
         let manager2 = EvaluatorManager()
         let manager3 = EvaluatorManager()
-        async let evalautor1 = try manager1.newEvaluator(options: .preconfigured).evaluateOutputText(source: .text("res = \"evaluator 1\""))
-        async let evalautor2 = try manager2.newEvaluator(options: .preconfigured).evaluateOutputText(source: .text("res = \"evaluator 2\""))
-        async let evalautor3 = try manager3.newEvaluator(options: .preconfigured).evaluateOutputText(source: .text("res = \"evaluator 3\""))
-        let (result1, result2, result3) = try await (evalautor1, evalautor2, evalautor3)
+        async let evaluator1 = try manager1.newEvaluator(options: .preconfigured).evaluateOutputText(source: .text("res = \"evaluator 1\""))
+        async let evaluator2 = try manager2.newEvaluator(options: .preconfigured).evaluateOutputText(source: .text("res = \"evaluator 2\""))
+        async let evaluator3 = try manager3.newEvaluator(options: .preconfigured).evaluateOutputText(source: .text("res = \"evaluator 3\""))
+        let (result1, result2, result3) = try await (evaluator1, evaluator2, evaluator3)
         XCTAssertEqual(result1, "res = \"evaluator 1\"\n")
         XCTAssertEqual(result2, "res = \"evaluator 2\"\n")
         XCTAssertEqual(result3, "res = \"evaluator 3\"\n")

Tests/PklSwiftTests/EvaluatorTest.swift

@@ -1,22 +1,22 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
-import Foundation
 @testable import MessagePack
 @testable import PklSwift
+import SemanticVersion
 import XCTest
 
 class TestLogger: Logger {
@@ -91,6 +91,33 @@ final class PklSwiftTests: XCTestCase {
         XCTAssertEqual(output, "foo = 1\n")
     }
 
+    func testVersionCoverage() async throws {
+        let output = try await SemanticVersion(EvaluatorManager().getVersion())!
+        XCTAssert(supportedPklVersions.contains { $0.major == output.major && $0.minor == output.minor })
+    }
+
+    func testCustomProxyOptions() async throws {
+        let version = try await SemanticVersion(EvaluatorManager().getVersion())!
+        let expected = version < pklVersion0_26
+            ? "http options are not supported on Pkl versions lower than 0.26"
+            : "ConnectException: Error connecting to host `example.com`"
+        var options = EvaluatorOptions.preconfigured
+        options.http = .init(
+            caCertificates: nil,
+            proxy: .init(
+                address: "http://localhost:1",
+                noProxy: ["myhost.com:1337", "myotherhost.org:42"]
+            )
+        )
+        do {
+            let evaluator = try await manager.newEvaluator(options: options)
+            let _ = try await evaluator.evaluateOutputText(source: .uri("https://example.com")!)
+            XCTFail("Should have thrown an error")
+        } catch {
+            XCTAssert("\(error)".contains(expected))
+        }
+    }
+
     func testCustomModuleReader() async throws {
         let reader = VirtualModuleReader(
             read: { _ in
@@ -278,10 +305,10 @@ final class PklSwiftTests: XCTestCase {
         XCTAssertEqual(logger.logLines, [#"pkl: TRACE: "Hello there" = "Hello there" (repl:text)\#n"#])
     }
 
-// TODO re-enable this test when packages are available
+    // TODO: re-enable this test when packages are available
 //
 //    func testWithProject() async throws {
-//        let project1Dir = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("project1")
+//        let project1Dir = (try tempDir()).appendingPathComponent("project1")
 //        try FileManager.default.createDirectory(at: project1Dir, withIntermediateDirectories: true)
 //        try """
 //        amends "pkl:Project"

Tests/PklSwiftTests/ExternalReaderClientTest.swift

@@ -0,0 +1,65 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import SemanticVersion
+import XCTest
+
+@testable import PklSwift
+
+class ExternalReaderClientTest: XCTestCase {
+    func testE2E() async throws {
+        let version = try await SemanticVersion(EvaluatorManager().getVersion())!
+        guard version >= pklVersion0_27 else {
+            throw XCTSkip("External readers require Pkl 0.27 or later.")
+        }
+
+        let tempDir = try tempDir()
+        let testFile = tempDir.appendingPathComponent("test.pkl")
+        try #"""
+        import "pkl:test"
+
+        fib5 = read("fib:5").text.toInt()
+        fib10 = read("fib:10").text.toInt()
+        fib20 = read("fib:20").text.toInt()
+
+        fibErrA = test.catch(() -> read("fib:%20"))
+        fibErrB = test.catch(() -> read("fib:abc"))
+        fibErrC = test.catch(() -> read("fib:-10"))
+        """#.write(to: testFile, atomically: true, encoding: .utf8)
+
+        let expectedResult = """
+        fib5 = 5
+        fib10 = 55
+        fib20 = 6765
+        fibErrA = "I/O error reading resource `fib:%20`. IOException: PklError(message: \\"input uri must be in format fib:<positive integer>\\")"
+        fibErrB = "I/O error reading resource `fib:abc`. IOException: PklError(message: \\"input uri must be in format fib:<positive integer>\\")"
+        fibErrC = "I/O error reading resource `fib:-10`. IOException: PklError(message: \\"input uri must be in format fib:<positive integer>\\")"
+        """
+
+        let opts = EvaluatorOptions(
+            allowedModules: ["file:", "repl:text"],
+            allowedResources: ["fib:", "prop:"],
+            externalResourceReaders: [
+                "fib": ExternalReader(executable: "./.build/debug/test-external-reader"),
+            ]
+        )
+
+        try await withEvaluator(options: opts) { evaluator in
+            let result = try await evaluator.evaluateOutputText(source: .url(testFile))
+            XCTAssertEqual(result.trimmingCharacters(in: .whitespacesAndNewlines), expectedResult.trimmingCharacters(in: .whitespacesAndNewlines))
+        }
+    }
+}

Tests/PklSwiftTests/Fixtures/ApiTypes.pkl

@@ -1,3 +1,2 @@
-res1: Pair<Int, String> = Pair(42, "Hello")
-res2: Duration = 10.h
-res3: DataSize = 1.2345.gib
+res1: Duration = 10.h
+res2: DataSize = 1.2345.gib

Tests/PklSwiftTests/Fixtures/Generated/AnyType.pkl.swift

@@ -5,7 +5,7 @@ public enum AnyType {}
 
 extension AnyType {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "AnyType"
+        public static let registeredIdentifier: String = "AnyType"
 
         public var bird: AnyHashable?
 
@@ -63,7 +63,7 @@ extension AnyType {
     }
 
     public struct Bird: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "AnyType#Bird"
+        public static let registeredIdentifier: String = "AnyType#Bird"
 
         public var species: String
 

Tests/PklSwiftTests/Fixtures/Generated/ApiTypes.pkl.swift

@@ -5,18 +5,15 @@ public enum ApiTypes {}
 
 extension ApiTypes {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "ApiTypes"
+        public static let registeredIdentifier: String = "ApiTypes"
 
-        public var res1: Pair<Int, String>
+        public var res1: Duration
 
-        public var res2: Duration
+        public var res2: DataSize
 
-        public var res3: DataSize
-
-        public init(res1: Pair<Int, String>, res2: Duration, res3: DataSize) {
+        public init(res1: Duration, res2: DataSize) {
             self.res1 = res1
             self.res2 = res2
-            self.res3 = res3
         }
     }
 

Tests/PklSwiftTests/Fixtures/Generated/Classes.pkl.swift

@@ -5,7 +5,7 @@ public enum Classes {}
 
 extension Classes {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Classes"
+        public static let registeredIdentifier: String = "Classes"
 
         public var animals: [Animal]
 
@@ -15,7 +15,7 @@ extension Classes {
     }
 
     public struct Animal: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Classes#Animal"
+        public static let registeredIdentifier: String = "Classes#Animal"
 
         public var name: String
 

Tests/PklSwiftTests/Fixtures/Generated/Collections.pkl.swift

@@ -5,7 +5,7 @@ public enum Collections {}
 
 extension Collections {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Collections"
+        public static let registeredIdentifier: String = "Collections"
 
         public var res1: [Int]
 

Tests/PklSwiftTests/Fixtures/Generated/ExtendedModule.pkl.swift

@@ -5,7 +5,7 @@ public enum ExtendedModule {}
 
 extension ExtendedModule {
     public struct Module: OpenModule.Module {
-        public static var registeredIdentifier: String = "ExtendedModule"
+        public static let registeredIdentifier: String = "ExtendedModule"
 
         public var foo: String
 

Tests/PklSwiftTests/Fixtures/Generated/OpenModule.pkl.swift

@@ -13,7 +13,7 @@ extension OpenModule {
     public typealias Module = OpenModule_Module
 
     public struct ModuleImpl: Module {
-        public static var registeredIdentifier: String = "OpenModule"
+        public static let registeredIdentifier: String = "OpenModule"
 
         public var foo: String
 

Tests/PklSwiftTests/Fixtures/Generated/UnionTypes.pkl.swift

@@ -7,6 +7,9 @@ public protocol UnionTypes_Animal: PklRegisteredType, DynamicallyEquatable, Hash
     var name: String { get }
 }
 
+public protocol UnionTypes_Shape: PklRegisteredType, DynamicallyEquatable, Hashable {
+}
+
 extension UnionTypes {
     public enum Fruit: Decodable, Hashable {
         case banana(Banana)
@@ -14,8 +17,9 @@ extension UnionTypes {
         case apple(Apple)
 
         public init(from decoder: Decoder) throws {
-            let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value
-            switch decoded {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
             case let decoded as Banana:
                 self = Fruit.banana(decoded)
             case let decoded as Grape:
@@ -27,14 +31,14 @@ extension UnionTypes {
                     Fruit.self,
                     .init(
                         codingPath: decoder.codingPath,
-                        debugDescription: "Expected type Fruit, but got \(String(describing: decoded))"
+                        debugDescription: "Expected type Fruit, but got \(String(describing: value))"
                     )
                 )
             }
         }
     }
 
-    public enum City: String, CaseIterable, Decodable, Hashable {
+    public enum City: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case sanFrancisco = "San Francisco"
         case tokyo = "Tokyo"
         case zurich = "Zurich"
@@ -46,8 +50,9 @@ extension UnionTypes {
         case donkey(Donkey)
 
         public init(from decoder: Decoder) throws {
-            let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value
-            switch decoded {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
             case let decoded as Zebra:
                 self = ZebraOrDonkey.zebra(decoded)
             case let decoded as Donkey:
@@ -57,7 +62,7 @@ extension UnionTypes {
                     ZebraOrDonkey.self,
                     .init(
                         codingPath: decoder.codingPath,
-                        debugDescription: "Expected type ZebraOrDonkey, but got \(String(describing: decoded))"
+                        debugDescription: "Expected type ZebraOrDonkey, but got \(String(describing: value))"
                     )
                 )
             }
@@ -80,8 +85,9 @@ extension UnionTypes {
         }
 
         public init(from decoder: Decoder) throws {
-            let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value
-            switch decoded {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
             case let decoded as any Animal:
                 self = AnimalOrString.animal(decoded)
             case let decoded as String:
@@ -91,7 +97,7 @@ extension UnionTypes {
                     AnimalOrString.self,
                     .init(
                         codingPath: decoder.codingPath,
-                        debugDescription: "Expected type AnimalOrString, but got \(String(describing: decoded))"
+                        debugDescription: "Expected type AnimalOrString, but got \(String(describing: value))"
                     )
                 )
             }
@@ -107,8 +113,116 @@ extension UnionTypes {
         }
     }
 
+    public enum IntOrFloat: Decodable, Hashable {
+        case int(Int)
+        case float64(Float64)
+
+        private static func decodeNumeric(from decoder: Decoder, _ container: any SingleValueDecodingContainer) -> IntOrFloat? {
+            return (try? .int(container.decode(Int.self)))
+                ?? (try? .float64(container.decode(Float64.self)))
+        }
+
+        public init(from decoder: Decoder) throws {
+            let container = try decoder.singleValueContainer()
+            let decoded = IntOrFloat.decodeNumeric(from: decoder, container)
+            if decoded != nil {
+                self = decoded!
+                return
+            }
+            let value = try container.decode(PklSwift.PklAny.self).value
+            throw DecodingError.typeMismatch(
+                IntOrFloat.self,
+                .init(
+                    codingPath: decoder.codingPath,
+                    debugDescription: "Expected type IntOrFloat, but got \(String(describing: value))"
+                )
+            )
+        }
+    }
+
+    public enum Environment: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
+        case dev = "dev"
+        case prod = "prod"
+        case qa = "qa"
+    }
+
+    public enum AnimalOrShape: Decodable, Hashable {
+        case animal(any Animal)
+        case shape(any Shape)
+
+        public static func ==(lhs: AnimalOrShape, rhs: AnimalOrShape) -> Bool {
+            switch (lhs, rhs) {
+            case let (.animal(a), .animal(b)):
+                return a.isDynamicallyEqual(to: b)
+            case let (.shape(a), .shape(b)):
+                return a.isDynamicallyEqual(to: b)
+            default:
+                return false
+            }
+        }
+
+        public init(from decoder: Decoder) throws {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
+            case let decoded as any Animal:
+                self = AnimalOrShape.animal(decoded)
+            case let decoded as any Shape:
+                self = AnimalOrShape.shape(decoded)
+            default:
+                throw DecodingError.typeMismatch(
+                    AnimalOrShape.self,
+                    .init(
+                        codingPath: decoder.codingPath,
+                        debugDescription: "Expected type AnimalOrShape, but got \(String(describing: value))"
+                    )
+                )
+            }
+        }
+
+        public func hash(into hasher: inout Hasher) {
+            switch self {
+            case let .animal(value):
+                hasher.combine(value)
+            case let .shape(value):
+                hasher.combine(value)
+            }
+        }
+    }
+
+    public enum Numbers: Decodable, Hashable {
+        case int8(Int8)
+        case int16(Int16)
+        case int32(Int32)
+        case int(Int)
+
+        private static func decodeNumeric(from decoder: Decoder, _ container: any SingleValueDecodingContainer) -> Numbers? {
+            return (try? .int8(container.decode(Int8.self)))
+                ?? (try? .int16(container.decode(Int16.self)))
+                ?? (try? .int32(container.decode(Int32.self)))
+                ?? (try? .int(container.decode(Int.self)))
+        }
+
+        public init(from decoder: Decoder) throws {
+            let container = try decoder.singleValueContainer()
+            let decoded = Numbers.decodeNumeric(from: decoder, container)
+            if decoded != nil {
+                self = decoded!
+                return
+            }
+            let value = try container.decode(PklSwift.PklAny.self).value
+            throw DecodingError.typeMismatch(
+                Numbers.self,
+                .init(
+                    codingPath: decoder.codingPath,
+                    debugDescription: "Expected type Numbers, but got \(String(describing: value))"
+                )
+            )
+        }
+    }
+
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "UnionTypes"
+        public static let registeredIdentifier: String = "UnionTypes"
 
         public var fruit1: Fruit
 
@@ -132,6 +246,26 @@ extension UnionTypes {
 
         public var animalOrString2: AnimalOrString
 
+        public var intOrFloat1: IntOrFloat
+
+        public var intOrFloat2: IntOrFloat
+
+        public var intOrFloat3: IntOrFloat
+
+        public var config: [Environment: String]
+
+        public var animalOrShape1: AnimalOrShape
+
+        public var animalOrShape2: AnimalOrShape
+
+        public var numbers1: Numbers
+
+        public var numbers2: Numbers
+
+        public var numbers3: Numbers
+
+        public var numbers4: Numbers
+
         public init(
             fruit1: Fruit,
             fruit2: Fruit,
@@ -143,7 +277,17 @@ extension UnionTypes {
             animal1: ZebraOrDonkey,
             animal2: ZebraOrDonkey,
             animalOrString1: AnimalOrString,
-            animalOrString2: AnimalOrString
+            animalOrString2: AnimalOrString,
+            intOrFloat1: IntOrFloat,
+            intOrFloat2: IntOrFloat,
+            intOrFloat3: IntOrFloat,
+            config: [Environment: String],
+            animalOrShape1: AnimalOrShape,
+            animalOrShape2: AnimalOrShape,
+            numbers1: Numbers,
+            numbers2: Numbers,
+            numbers3: Numbers,
+            numbers4: Numbers
         ) {
             self.fruit1 = fruit1
             self.fruit2 = fruit2
@@ -156,11 +300,21 @@ extension UnionTypes {
             self.animal2 = animal2
             self.animalOrString1 = animalOrString1
             self.animalOrString2 = animalOrString2
+            self.intOrFloat1 = intOrFloat1
+            self.intOrFloat2 = intOrFloat2
+            self.intOrFloat3 = intOrFloat3
+            self.config = config
+            self.animalOrShape1 = animalOrShape1
+            self.animalOrShape2 = animalOrShape2
+            self.numbers1 = numbers1
+            self.numbers2 = numbers2
+            self.numbers3 = numbers3
+            self.numbers4 = numbers4
         }
     }
 
     public struct Banana: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "UnionTypes#Banana"
+        public static let registeredIdentifier: String = "UnionTypes#Banana"
 
         public var isRipe: Bool
 
@@ -170,7 +324,7 @@ extension UnionTypes {
     }
 
     public struct Grape: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "UnionTypes#Grape"
+        public static let registeredIdentifier: String = "UnionTypes#Grape"
 
         public var isUsedForWine: Bool
 
@@ -180,7 +334,7 @@ extension UnionTypes {
     }
 
     public struct Apple: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "UnionTypes#Apple"
+        public static let registeredIdentifier: String = "UnionTypes#Apple"
 
         public var isRed: Bool
 
@@ -191,8 +345,20 @@ extension UnionTypes {
 
     public typealias Animal = UnionTypes_Animal
 
+    public typealias Shape = UnionTypes_Shape
+
+    public struct Square: Shape {
+        public static let registeredIdentifier: String = "UnionTypes#Square"
+
+        public var corners: Int
+
+        public init(corners: Int) {
+            self.corners = corners
+        }
+    }
+
     public struct Zebra: Animal {
-        public static var registeredIdentifier: String = "UnionTypes#Zebra"
+        public static let registeredIdentifier: String = "UnionTypes#Zebra"
 
         public var name: String
 
@@ -202,7 +368,7 @@ extension UnionTypes {
     }
 
     public struct Donkey: Animal {
-        public static var registeredIdentifier: String = "UnionTypes#Donkey"
+        public static let registeredIdentifier: String = "UnionTypes#Donkey"
 
         public var name: String
 

Tests/PklSwiftTests/Fixtures/Generated/pkl_swift_example_Poly.pkl.swift

@@ -9,7 +9,7 @@ public protocol pkl_swift_example_Poly_Animal: pkl_swift_lib1_Being {
 
 extension pkl_swift_example_Poly {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "pkl.swift.example.Poly"
+        public static let registeredIdentifier: String = "pkl.swift.example.Poly"
 
         public var beings: [any pkl_swift_lib1.Being]
 
@@ -56,7 +56,7 @@ extension pkl_swift_example_Poly {
     }
 
     public struct Dog: Animal {
-        public static var registeredIdentifier: String = "pkl.swift.example.Poly#Dog"
+        public static let registeredIdentifier: String = "pkl.swift.example.Poly#Dog"
 
         public var barks: Bool
 
@@ -103,7 +103,7 @@ extension pkl_swift_example_Poly {
     public typealias Animal = pkl_swift_example_Poly_Animal
 
     public struct AnimalImpl: Animal {
-        public static var registeredIdentifier: String = "pkl.swift.example.Poly#Animal"
+        public static let registeredIdentifier: String = "pkl.swift.example.Poly#Animal"
 
         public var name: String
 
@@ -116,7 +116,7 @@ extension pkl_swift_example_Poly {
     }
 
     public struct Bird: pkl_swift_lib1.Being {
-        public static var registeredIdentifier: String = "pkl.swift.example.Poly#Bird"
+        public static let registeredIdentifier: String = "pkl.swift.example.Poly#Bird"
 
         public var name: String
 

Tests/PklSwiftTests/Fixtures/Generated/pkl_swift_lib1.pkl.swift

@@ -9,7 +9,7 @@ public protocol pkl_swift_lib1_Being: PklRegisteredType, DynamicallyEquatable, H
 
 extension pkl_swift_lib1 {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "pkl.swift.lib1"
+        public static let registeredIdentifier: String = "pkl.swift.lib1"
 
         public init() {}
     }

Tests/PklSwiftTests/Fixtures/UnionTypes.pkl

@@ -1,3 +1,5 @@
+import "pkl:math"
+
 class Banana {
   isRipe: Boolean
 }
@@ -18,6 +20,12 @@ typealias Fruit = Banana | Grape | Apple
 
 typealias City = "San Francisco"|"Tokyo"|"Zurich"|"London"
 
+abstract class Shape
+
+class Square extends Shape {
+  fixed corners: Int = 4
+}
+
 fruit1: Fruit = new Banana {
   isRipe = true
 }
@@ -52,4 +60,34 @@ typealias AnimalOrString = Animal|String
 
 animalOrString1: AnimalOrString = new Zebra {}
 
-animalOrString2: AnimalOrString = "Zebra"
+animalOrString2: AnimalOrString = "Zebra"
+
+typealias IntOrFloat = Int | Float
+
+intOrFloat1: IntOrFloat = 5.0
+
+intOrFloat2: IntOrFloat = 5.5
+
+intOrFloat3: IntOrFloat = 128
+
+typealias Environment = "dev"|"prod"|"qa"
+
+config: Mapping<Environment, String> = new {
+  ["dev"] = "Imaginary Service Company (ISC) configuration"
+}
+
+typealias AnimalOrShape = Animal|Shape
+
+animalOrShape1: AnimalOrShape = new Donkey {}
+
+animalOrShape2: AnimalOrShape = new Square {}
+
+typealias Numbers = Int8 | Int16 | Int32 | Int
+
+numbers1: Numbers = 5
+
+numbers2: Numbers = 128
+
+numbers3: Numbers = 32768
+
+numbers4: Numbers = math.maxInt

Tests/PklSwiftTests/FixturesTest.swift

@@ -1,18 +1,18 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 import PklSwift
 import XCTest
@@ -77,9 +77,8 @@ class FixturesTest: XCTestCase {
         XCTAssertEqual(
             result,
             ApiTypes.Module(
-                res1: Pair(42, "Hello"),
-                res2: .hours(10),
-                res3: .gibibytes(1.2345)
+                res1: .hours(10),
+                res2: .gibibytes(1.2345)
             )
         )
     }
@@ -161,7 +160,17 @@ class FixturesTest: XCTestCase {
             animal1: .zebra(UnionTypes.Zebra(name: "Zebra")),
             animal2: .donkey(UnionTypes.Donkey(name: "Donkey")),
             animalOrString1: .animal(UnionTypes.Zebra(name: "Zebra")),
-            animalOrString2: .string("Zebra")
+            animalOrString2: .string("Zebra"),
+            intOrFloat1: .float64(5.0),
+            intOrFloat2: .float64(5.5),
+            intOrFloat3: .int(128),
+            config: [.dev : "Imaginary Service Company (ISC) configuration"],
+            animalOrShape1: .animal(UnionTypes.Donkey(name: "Donkey")),
+            animalOrShape2: .shape(UnionTypes.Square(corners: 4)),
+            numbers1: .int8(5),
+            numbers2: .int16(128),
+            numbers3: .int32(32768),
+            numbers4: .int(Int.max)
         ))
     }
 }

Tests/PklSwiftTests/ProjectTest.swift

@@ -1,32 +1,34 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
-import Foundation
+import SemanticVersion
 import XCTest
 
 @testable import PklSwift
 
 class ProjectTest: XCTestCase {
     func testLoadProject() async throws {
-        let tempDir = NSTemporaryDirectory()
-        try FileManager.default.createDirectory(atPath: tempDir + "/subdir", withIntermediateDirectories: true)
-        let otherProjectFile = URL(fileURLWithPath: tempDir, isDirectory: true)
-            .appendingPathComponent("subdir/PklProject")
+        let version = try await SemanticVersion(EvaluatorManager().getVersion())!
+        let tempDir = try tempDir()
+        let subDir = tempDir.appendingPathComponent("subdir")
+        try FileManager.default.createDirectory(at: subDir, withIntermediateDirectories: true)
+        let otherProjectFile = subDir.appendingPathComponent("PklProject")
 
         try #"""
+        @ModuleInfo { minPklVersion = "0.25.0" }
         amends "pkl:Project"
 
         package {
@@ -37,8 +39,53 @@ class ProjectTest: XCTestCase {
         }
         """#.write(to: otherProjectFile, atomically: true, encoding: .utf8)
 
-        let file = URL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true)
-            .appendingPathComponent("PklProject")
+        let file = try (PklSwift.tempDir()).appendingPathComponent("PklProject")
+
+        let httpSetting = version < pklVersion0_26 ? "" : """
+        http {
+          proxy {
+            address = "http://localhost:1"
+            noProxy {
+              "example.com"
+              "foo.bar.org"
+            }
+          }
+        }
+        """
+        let externalReaderSettings = version < pklVersion0_27 ? "" : """
+        externalModuleReaders {
+          ["scheme1"] {
+            executable = "reader1"
+          }
+          ["scheme2"] {
+            executable = "reader2"
+            arguments { "with"; "args" }
+          }
+        }
+        externalResourceReaders {
+          ["scheme3"] {
+            executable = "reader3"
+          }
+          ["scheme4"] {
+            executable = "reader4"
+            arguments { "with"; "args" }
+          }
+        }
+        """
+        let colorSetting = version < pklVersion0_27 ? "" : #"color = "always""#
+        let httpExpectation = version < pklVersion0_26 ? nil : Http(
+            caCertificates: nil,
+            proxy: .init(address: "http://localhost:1", noProxy: ["example.com", "foo.bar.org"])
+        )
+        let externalModuleReadersExpectation = version < pklVersion0_27 ? nil : [
+            "scheme1": ExternalReader(executable: "reader1"),
+            "scheme2": ExternalReader(executable: "reader2", arguments: ["with", "args"]),
+        ]
+        let externalResourceReadersExpectation = version < pklVersion0_27 ? nil : [
+            "scheme3": ExternalReader(executable: "reader3"),
+            "scheme4": ExternalReader(executable: "reader4", arguments: ["with", "args"]),
+        ]
+        let color: PklEvaluatorSettingsColor? = version < pklVersion0_27 ? nil : .always
         try #"""
         amends "pkl:Project"
 
@@ -83,6 +130,9 @@ class ProjectTest: XCTestCase {
           timeout = 5.min
           moduleCacheDir = "/bar/buzz"
           rootDir = "/buzzy"
+          \#(externalReaderSettings)
+          \#(httpSetting)
+          \#(colorSetting)
         }
 
         dependencies {
@@ -97,7 +147,7 @@ class ProjectTest: XCTestCase {
                 source: .url(file),
                 asType: Project.self
             )
-            let expectedSettings = PklSwift.Project.EvaluatorSettings(
+            let expectedSettings = PklSwift.PklEvaluatorSettings(
                 externalProperties: ["myprop": "1"],
                 env: ["myenv": "2"],
                 allowedModules: ["foo:"],
@@ -106,7 +156,11 @@ class ProjectTest: XCTestCase {
                 modulePath: ["/bar/baz"],
                 timeout: .minutes(5),
                 moduleCacheDir: "/bar/buzz",
-                rootDir: "/buzzy"
+                rootDir: "/buzzy",
+                http: httpExpectation,
+                externalModuleReaders: externalModuleReadersExpectation,
+                externalResourceReaders: externalResourceReadersExpectation,
+                color: color
             )
             let expectedPackage = PklSwift.Project.Package(
                 name: "hawk",
@@ -160,7 +214,11 @@ class ProjectTest: XCTestCase {
                         modulePath: nil,
                         timeout: nil,
                         moduleCacheDir: nil,
-                        rootDir: nil
+                        rootDir: nil,
+                        http: nil,
+                        externalModuleReaders: nil,
+                        externalResourceReaders: nil,
+                        color: nil
                     ),
                     projectFileUri: "\(otherProjectFile)",
                     tests: [],

VERSION.txt

@@ -1 +1 @@
-0.2.3
+0.4.2

codegen/snippet-tests/output/Classes.pkl.swift

@@ -9,7 +9,7 @@ public protocol Classes_Animal: PklRegisteredType, DynamicallyEquatable, Hashabl
 
 extension Classes {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Classes"
+        public static let registeredIdentifier: String = "Classes"
 
         public var animals: [any Animal]
 
@@ -38,7 +38,7 @@ extension Classes {
     public typealias Animal = Classes_Animal
 
     public struct AnimalImpl: Animal {
-        public static var registeredIdentifier: String = "Classes#Animal"
+        public static let registeredIdentifier: String = "Classes#Animal"
 
         public var name: String
 

codegen/snippet-tests/output/EmptyOpenModule.pkl.swift

@@ -10,7 +10,7 @@ extension EmptyOpenModule {
     public typealias Module = EmptyOpenModule_Module
 
     public struct ModuleImpl: Module {
-        public static var registeredIdentifier: String = "EmptyOpenModule"
+        public static let registeredIdentifier: String = "EmptyOpenModule"
 
         public init() {}
     }

codegen/snippet-tests/output/Enums.pkl.swift

@@ -5,7 +5,7 @@ public enum Enums {}
 
 extension Enums {
     /// City is one of these four fantastic cities
-    public enum City: String, CaseIterable, Decodable, Hashable {
+    public enum City: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case sanFrancisco = "San Francisco"
         case london = "London"
         case zurich = "Zurich"
@@ -19,8 +19,9 @@ extension Enums {
         case monkey(Monkey)
 
         public init(from decoder: Decoder) throws {
-            let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value
-            switch decoded {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
             case let decoded as Horse:
                 self = Animal.horse(decoded)
             case let decoded as Zebra:
@@ -32,7 +33,7 @@ extension Enums {
                     Animal.self,
                     .init(
                         codingPath: decoder.codingPath,
-                        debugDescription: "Expected type Animal, but got \(String(describing: decoded))"
+                        debugDescription: "Expected type Animal, but got \(String(describing: value))"
                     )
                 )
             }
@@ -45,8 +46,9 @@ extension Enums {
         case arrayString([String])
 
         public init(from decoder: Decoder) throws {
-            let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value
-            switch decoded {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
             case let decoded as [String: String]:
                 self = DictOrArray.dictionaryStringString(decoded)
             case let decoded as [String]:
@@ -56,7 +58,7 @@ extension Enums {
                     DictOrArray.self,
                     .init(
                         codingPath: decoder.codingPath,
-                        debugDescription: "Expected type DictOrArray, but got \(String(describing: decoded))"
+                        debugDescription: "Expected type DictOrArray, but got \(String(describing: value))"
                     )
                 )
             }
@@ -69,8 +71,9 @@ extension Enums {
         case string(String)
 
         public init(from decoder: Decoder) throws {
-            let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value
-            switch decoded {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
             case let decoded as Horse:
                 self = HorseOrBug.horse(decoded)
             case let decoded as String:
@@ -82,7 +85,7 @@ extension Enums {
                     HorseOrBug.self,
                     .init(
                         codingPath: decoder.codingPath,
-                        debugDescription: "Expected type HorseOrBug, but got \(String(describing: decoded))"
+                        debugDescription: "Expected type HorseOrBug, but got \(String(describing: value))"
                     )
                 )
             }
@@ -94,8 +97,9 @@ extension Enums {
         case zebra(Zebra)
 
         public init(from decoder: Decoder) throws {
-            let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value
-            switch decoded {
+            let container = try decoder.singleValueContainer()
+            let value = try container.decode(PklSwift.PklAny.self).value
+            switch value?.base {
             case let decoded as Horse?:
                 self = MaybeHorseOrDefinitelyZebra.horse(decoded)
             case let decoded as Zebra:
@@ -105,7 +109,7 @@ extension Enums {
                     MaybeHorseOrDefinitelyZebra.self,
                     .init(
                         codingPath: decoder.codingPath,
-                        debugDescription: "Expected type MaybeHorseOrDefinitelyZebra, but got \(String(describing: decoded))"
+                        debugDescription: "Expected type MaybeHorseOrDefinitelyZebra, but got \(String(describing: value))"
                     )
                 )
             }
@@ -113,7 +117,7 @@ extension Enums {
     }
 
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Enums"
+        public static let registeredIdentifier: String = "Enums"
 
         /// City of tomorrow!
         public var city: City
@@ -145,7 +149,7 @@ extension Enums {
     }
 
     public struct Horse: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Enums#Horse"
+        public static let registeredIdentifier: String = "Enums#Horse"
 
         public var neigh: Bool
 
@@ -155,7 +159,7 @@ extension Enums {
     }
 
     public struct Zebra: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Enums#Zebra"
+        public static let registeredIdentifier: String = "Enums#Zebra"
 
         public var stripes: String
 
@@ -165,7 +169,7 @@ extension Enums {
     }
 
     public struct Monkey: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Enums#Monkey"
+        public static let registeredIdentifier: String = "Enums#Monkey"
 
         public var tail: String
 

codegen/snippet-tests/output/ExplicitlyCoolName.pkl.swift

@@ -4,13 +4,13 @@ import PklSwift
 public enum ExplicitlyCoolName {}
 
 extension ExplicitlyCoolName {
-    public enum ConfigType: String, CaseIterable, Decodable, Hashable {
+    public enum ConfigType: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case one = "one"
         case two = "two"
     }
 
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "ExplicitName"
+        public static let registeredIdentifier: String = "ExplicitName"
 
         public var MyCoolProp: SomethingVeryFunny
 
@@ -24,7 +24,7 @@ extension ExplicitlyCoolName {
     }
 
     public struct SomethingVeryFunny: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "ExplicitName#SomethingFunny"
+        public static let registeredIdentifier: String = "ExplicitName#SomethingFunny"
 
         public init() {}
     }

codegen/snippet-tests/output/ExtendModule.pkl.swift

@@ -5,7 +5,7 @@ public enum ExtendModule {}
 
 extension ExtendModule {
     public struct Module: MyModule.Module {
-        public static var registeredIdentifier: String = "ExtendModule"
+        public static let registeredIdentifier: String = "ExtendModule"
 
         public var bar: String
 

codegen/snippet-tests/output/ExtendingOpenClass.pkl.swift

@@ -9,7 +9,7 @@ public protocol ExtendingOpenClass_MyOpenClass: PklRegisteredType, DynamicallyEq
 
 extension ExtendingOpenClass {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "ExtendingOpenClass"
+        public static let registeredIdentifier: String = "ExtendingOpenClass"
 
         public var res1: MyClass
 
@@ -22,7 +22,7 @@ extension ExtendingOpenClass {
     }
 
     public struct MyClass: MyOpenClass {
-        public static var registeredIdentifier: String = "ExtendingOpenClass#MyClass"
+        public static let registeredIdentifier: String = "ExtendingOpenClass#MyClass"
 
         public var myBoolean: Bool
 
@@ -37,7 +37,7 @@ extension ExtendingOpenClass {
     public typealias MyOpenClass = ExtendingOpenClass_MyOpenClass
 
     public struct MyOpenClassImpl: MyOpenClass {
-        public static var registeredIdentifier: String = "ExtendingOpenClass#MyOpenClass"
+        public static let registeredIdentifier: String = "ExtendingOpenClass#MyOpenClass"
 
         public var myStr: String
 
@@ -47,7 +47,7 @@ extension ExtendingOpenClass {
     }
 
     public struct MyClass2: lib3.GoGoGo {
-        public static var registeredIdentifier: String = "ExtendingOpenClass#MyClass2"
+        public static let registeredIdentifier: String = "ExtendingOpenClass#MyClass2"
 
         public var myBoolean: Bool
 

codegen/snippet-tests/output/ExtendsAbstractClass.pkl.swift

@@ -9,7 +9,7 @@ public protocol ExtendsAbstractClass_A: PklRegisteredType, DynamicallyEquatable,
 
 extension ExtendsAbstractClass {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "ExtendsAbstractClass"
+        public static let registeredIdentifier: String = "ExtendsAbstractClass"
 
         public var a: any A
 
@@ -36,7 +36,7 @@ extension ExtendsAbstractClass {
     public typealias A = ExtendsAbstractClass_A
 
     public struct B: A {
-        public static var registeredIdentifier: String = "ExtendsAbstractClass#B"
+        public static let registeredIdentifier: String = "ExtendsAbstractClass#B"
 
         public var c: String
 

codegen/snippet-tests/output/Foo.pkl.swift

@@ -13,7 +13,7 @@ public protocol Foo_Being: PklRegisteredType, DynamicallyEquatable, Hashable {
 
 extension Foo {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Foo"
+        public static let registeredIdentifier: String = "Foo"
 
         public var animals: [any Animal]
 
@@ -42,7 +42,7 @@ extension Foo {
     public typealias Animal = Foo_Animal
 
     public struct AnimalImpl: Animal {
-        public static var registeredIdentifier: String = "Foo#Animal"
+        public static let registeredIdentifier: String = "Foo#Animal"
 
         public var name: String
 
@@ -57,7 +57,7 @@ extension Foo {
     public typealias Being = Foo_Being
 
     public struct Bird: Animal {
-        public static var registeredIdentifier: String = "Foo#Bird"
+        public static let registeredIdentifier: String = "Foo#Bird"
 
         public var flies: Bool
 
@@ -73,7 +73,7 @@ extension Foo {
     }
 
     public struct Dog: Animal {
-        public static var registeredIdentifier: String = "Foo#Dog"
+        public static let registeredIdentifier: String = "Foo#Dog"
 
         public var barks: Bool
 

codegen/snippet-tests/output/HiddenProperties.pkl.swift

@@ -5,7 +5,7 @@ public enum HiddenProperties {}
 
 extension HiddenProperties {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "HiddenProperties"
+        public static let registeredIdentifier: String = "HiddenProperties"
 
         public var propC: String
 

codegen/snippet-tests/output/Imports.pkl.swift

@@ -5,7 +5,7 @@ public enum Imports {}
 
 extension Imports {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "Imports"
+        public static let registeredIdentifier: String = "Imports"
 
         public var foo: Foo.Module
 

codegen/snippet-tests/output/MyModule.pkl.swift

@@ -11,7 +11,7 @@ extension MyModule {
     public typealias Module = MyModule_Module
 
     public struct ModuleImpl: Module {
-        public static var registeredIdentifier: String = "MyModule"
+        public static let registeredIdentifier: String = "MyModule"
 
         public var foo: String
 

codegen/snippet-tests/output/Override2.pkl.swift

@@ -11,7 +11,7 @@ extension Override2 {
     public typealias Module = Override2_Module
 
     public struct ModuleImpl: Module {
-        public static var registeredIdentifier: String = "Override2"
+        public static let registeredIdentifier: String = "Override2"
 
         /// Doc comments
         public var foo: String
@@ -22,7 +22,7 @@ extension Override2 {
     }
 
     public struct MySubclass: Module {
-        public static var registeredIdentifier: String = "Override2#MySubclass"
+        public static let registeredIdentifier: String = "Override2#MySubclass"
 
         /// Doc comments
         public var foo: String

codegen/snippet-tests/output/TypeAliased.pkl.swift

@@ -5,7 +5,7 @@ public enum TypeAliased {}
 
 extension TypeAliased {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "TypeAliased"
+        public static let registeredIdentifier: String = "TypeAliased"
 
         public var myMap: StringyMap
 

codegen/snippet-tests/output/UnionNameKeyword.pkl.swift

@@ -4,14 +4,14 @@ import PklSwift
 public enum UnionNameKeyword {}
 
 extension UnionNameKeyword {
-    public enum `Type`: String, CaseIterable, Decodable, Hashable {
+    public enum `Type`: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case one = "one"
         case two = "two"
         case three = "three"
     }
 
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "UnionNameKeyword"
+        public static let registeredIdentifier: String = "UnionNameKeyword"
 
         public var type: `Type`
 

codegen/snippet-tests/output/com_example_ExtendedSimple.pkl.swift

@@ -5,13 +5,13 @@ public enum com_example_ExtendedSimple {}
 
 extension com_example_ExtendedSimple {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "com.example.ExtendedSimple"
+        public static let registeredIdentifier: String = "com.example.ExtendedSimple"
 
         public init() {}
     }
 
     public struct ExtendedSimple: com_example_Simple.Person {
-        public static var registeredIdentifier: String = "com.example.ExtendedSimple#ExtendedSimple"
+        public static let registeredIdentifier: String = "com.example.ExtendedSimple#ExtendedSimple"
 
         public var eyeColor: String
 

codegen/snippet-tests/output/com_example_Simple.pkl.swift

@@ -15,7 +15,7 @@ public protocol com_example_Simple_OpenClassExtendingOpenClass: PklRegisteredTyp
 
 extension com_example_Simple {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "com.example.Simple"
+        public static let registeredIdentifier: String = "com.example.Simple"
 
         /// This is truly a person.
         public var person: any Person
@@ -43,7 +43,7 @@ extension com_example_Simple {
     public typealias Person = com_example_Simple_Person
 
     public struct PersonImpl: Person {
-        public static var registeredIdentifier: String = "com.example.Simple#Person"
+        public static let registeredIdentifier: String = "com.example.Simple#Person"
 
         /// The name of the person
         public var theName: String
@@ -63,7 +63,7 @@ extension com_example_Simple {
     }
 
     public struct ThePerson: Person {
-        public static var registeredIdentifier: String = "com.example.Simple#ThePerson"
+        public static let registeredIdentifier: String = "com.example.Simple#ThePerson"
 
         public var the: String
 
@@ -89,7 +89,7 @@ extension com_example_Simple {
     public typealias OpenClassExtendingOpenClass = com_example_Simple_OpenClassExtendingOpenClass
 
     public struct OpenClassExtendingOpenClassImpl: OpenClassExtendingOpenClass {
-        public static var registeredIdentifier: String = "com.example.Simple#OpenClassExtendingOpenClass"
+        public static let registeredIdentifier: String = "com.example.Simple#OpenClassExtendingOpenClass"
 
         public var someOtherProp: Bool?
 
@@ -99,7 +99,7 @@ extension com_example_Simple {
     }
 
     public struct ClassWithReallyLongConstructor: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "com.example.Simple#ClassWithReallyLongConstructor"
+        public static let registeredIdentifier: String = "com.example.Simple#ClassWithReallyLongConstructor"
 
         public var theProperty1: String
 

codegen/snippet-tests/output/lib3.pkl.swift

@@ -11,7 +11,7 @@ extension lib3 {
     public typealias GoGoGo = lib3_GoGoGo
 
     public struct GoGoGoImpl: GoGoGo {
-        public static var registeredIdentifier: String = "lib3#GoGoGo"
+        public static let registeredIdentifier: String = "lib3#GoGoGo"
 
         public var duck: String
 
@@ -21,7 +21,7 @@ extension lib3 {
     }
 
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "lib3"
+        public static let registeredIdentifier: String = "lib3"
 
         public init() {}
     }

codegen/snippet-tests/output/override.pkl.swift

@@ -9,7 +9,7 @@ public protocol override_Foo: PklRegisteredType, DynamicallyEquatable, Hashable
 
 extension override {
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "override"
+        public static let registeredIdentifier: String = "override"
 
         public var foo: any Foo
 
@@ -36,7 +36,7 @@ extension override {
     public typealias Foo = override_Foo
 
     public struct Bar: Foo {
-        public static var registeredIdentifier: String = "override#Bar"
+        public static let registeredIdentifier: String = "override#Bar"
 
         public var myProp: String
 

codegen/snippet-tests/output/union.pkl.swift

@@ -5,28 +5,28 @@ public enum union {}
 
 extension union {
     /// City; e.g. where people live
-    public enum City: String, CaseIterable, Decodable, Hashable {
+    public enum City: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case sanFrancisco = "San Francisco"
         case london = "London"
         case 上海 = "上海"
     }
 
     /// Locale that contains cities and towns
-    public enum County: String, CaseIterable, Decodable, Hashable {
+    public enum County: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case sanFrancisco = "San Francisco"
         case sanMateo = "San Mateo"
         case yolo = "Yolo"
     }
 
     /// Noodles
-    public enum Noodles: String, CaseIterable, Decodable, Hashable {
+    public enum Noodles: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case 拉面 = "拉面"
         case 刀切面 = "刀切面"
         case 面线 = "面线"
         case 意大利面 = "意大利面"
     }
 
-    public enum AccountDisposition: String, CaseIterable, Decodable, Hashable {
+    public enum AccountDisposition: String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {
         case empty = ""
         case icloud3 = "icloud3"
         case prod = "prod"
@@ -34,7 +34,7 @@ extension union {
     }
 
     public struct Module: PklRegisteredType, Decodable, Hashable {
-        public static var registeredIdentifier: String = "union"
+        public static let registeredIdentifier: String = "union"
 
         /// A city
         public var city: City

codegen/src/Generator.pkl

@@ -1,18 +1,19 @@
-// ===----------------------------------------------------------------------===//
-// Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//	https://www.apache.org/licenses/LICENSE-2.0
+//   https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 /// Generates Swift sources from Pkl
 @swift.Module { name = "pkl_gen_swift" }
 @ModuleInfo { minPklVersion = "0.24.0" }

codegen/src/GeneratorSettings.pkl

@@ -1,3 +1,19 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
 /// Settings used to configure code generation.
 @swift.Module { name = "pkl_gen_swift" }
 @swift.Name { value = "GeneratorSettings" }

codegen/src/PklProject

@@ -1,3 +1,19 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
 amends "pkl:Project"
 
 package {

codegen/src/PklProject.deps.json

@@ -1,4 +1,4 @@
 {
   "schemaVersion": 1,
   "resolvedDependencies": {}
-}
+}