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 +13,7 @@
 // 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"
 
@@ -47,7 +47,7 @@ local class PklDistribution {
 }
 
 local pklCurrent: PklDistribution = new {
-  version = "0.26.0"
+  version = "0.27.2"
 }
 
 local pklDistributions: Listing<PklDistribution> = new {
@@ -133,6 +133,7 @@ jobs {
         "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" }
@@ -143,6 +144,34 @@ jobs {
     }
   }
 
+  ["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"
+      }
+    }
+    steps {
+      "checkout"
+      new RunStep {
+        command = "make swiftformat-lint"
+      }
+    }
+  }
+
   ["pkl-gen-swift-macos"] {
     macos {
       xcode = "15.2.0"

.circleci/config.yml

@@ -18,6 +18,8 @@ jobs:
           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:
@@ -29,21 +31,23 @@ jobs:
     resource_class: xlarge
     docker:
     - image: swift:5.9-rhel-ubi9
-  test-pkl-0-26-0:
+  test-pkl-0-27-2:
     steps:
     - checkout
     - run:
         command: |-
-          PKL=$(mktemp /tmp/pkl-0.26.0-XXXXXX)
+          PKL=$(mktemp /tmp/pkl-0.27.2-XXXXXX)
-          curl -L "https://github.com/apple/pkl/releases/download/0.26.0/pkl-linux-amd64" > $PKL
+          curl -L "https://github.com/apple/pkl/releases/download/0.27.2/pkl-linux-amd64" > $PKL
           chmod +x $PKL
           echo "export PKL_EXEC=$PKL" >> $BASH_ENV
-        name: Downloading pkl-0.26.0
+        name: Downloading pkl-0.27.2
     - run:
         command: |-
           mkdir -p .out/test-results/
           swift test -vv --parallel --num-workers 1 --xunit-output .out/test-results/xunit.xml -Xswiftc -warnings-as-errors
         name: swift test
+    - run:
+        command: make circleci-config
     - run:
         command: make test-snippets
     - run:
@@ -55,6 +59,20 @@ jobs:
     resource_class: xlarge
     docker:
     - image: swift:5.9-rhel-ubi9
+  test-license-headers:
+    steps:
+    - checkout
+    - run:
+        command: /bin/hawkeye check --fail-if-unknown
+    docker:
+    - image: ghcr.io/korandoru/hawkeye
+  test-format:
+    steps:
+    - checkout
+    - run:
+        command: make swiftformat-lint
+    docker:
+    - image: swift:5.9-rhel-ubi9
   pkl-gen-swift-macos:
     steps:
     - checkout
@@ -108,11 +126,11 @@ jobs:
     - checkout
     - run:
         command: |-
-          PKL=$(mktemp /tmp/pkl-0.26.0-XXXXXX)
+          PKL=$(mktemp /tmp/pkl-0.27.2-XXXXXX)
-          curl -L "https://github.com/apple/pkl/releases/download/0.26.0/pkl-linux-amd64" > $PKL
+          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-0.26.0
+        name: Downloading pkl-0.27.2
     - run:
         command: $PKL_EXEC project package --skip-publish-check --output-path out/pkl-package/ codegen/src/
     - persist_to_workspace:
@@ -193,11 +211,15 @@ workflows:
     - test-pkl-0-25-3:
         requires:
         - hold
-        - pr-approval/authenticate
+    - test-pkl-0-27-2:
-    - test-pkl-0-26-0:
+        requires:
+        - hold
+    - test-license-headers:
+        requires:
+        - hold
+    - test-format:
         requires:
         - hold
-        - pr-approval/authenticate
     when:
       matches:
         value: << pipeline.git.branch >>
@@ -205,7 +227,9 @@ workflows:
   main:
     jobs:
     - test-pkl-0-25-3
-    - test-pkl-0-26-0
+    - test-pkl-0-27-2
+    - test-license-headers
+    - test-format
     when:
       equal:
       - main
@@ -218,7 +242,19 @@ workflows:
             ignore: /.*/
           tags:
             only: /^v?\d+\.\d+\.\d+$/
-    - test-pkl-0-26-0:
+    - 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: /.*/
@@ -227,7 +263,9 @@ workflows:
     - pkl-package:
         requires:
         - test-pkl-0-25-3
-        - test-pkl-0-26-0
+        - test-pkl-0-27-2
+        - test-license-headers
+        - test-format
         filters:
           branches:
             ignore: /.*/
@@ -236,7 +274,9 @@ workflows:
     - pkl-gen-swift-macos:
         requires:
         - test-pkl-0-25-3
-        - test-pkl-0-26-0
+        - test-pkl-0-27-2
+        - test-license-headers
+        - test-format
         filters:
           branches:
             ignore: /.*/
@@ -245,7 +285,9 @@ workflows:
     - pkl-gen-swift-linux-amd64:
         requires:
         - test-pkl-0-25-3
-        - test-pkl-0-26-0
+        - test-pkl-0-27-2
+        - test-license-headers
+        - test-format
         filters:
           branches:
             ignore: /.*/
@@ -254,7 +296,9 @@ workflows:
     - pkl-gen-swift-linux-aarch64:
         requires:
         - test-pkl-0-25-3
-        - test-pkl-0-26-0
+        - 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

@@ -18,6 +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",
@@ -26,6 +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(
@@ -25,6 +41,10 @@ let package = Package(
         .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(
@@ -48,6 +68,10 @@ let package = Package(
             ],
             resources: [.embedInCode("Resources/VERSION.txt")]
         ),
+        .executableTarget(
+            name: "test-external-reader",
+            dependencies: ["PklSwift"]
+        ),
         .testTarget(
             name: "PklSwiftTests",
             dependencies: [

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
 

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

@@ -1,18 +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/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/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

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
 

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
 

Sources/PklSwift/EvaluatorManager.swift

@@ -1,29 +1,30 @@
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
-// 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
+import WinSDK.System
-    let ENV_SEPARATOR=";"
+
-    let PKL_EXEC_NAME="pkl.exe"
+let ENV_SEPARATOR=";"
+let PKL_EXEC_NAME="pkl.exe"
 #else
-    let ENV_SEPARATOR=":"
+let ENV_SEPARATOR=":"
-    let PKL_EXEC_NAME="pkl"
+let PKL_EXEC_NAME="pkl"
 #endif
 /// Perfoms `action`, returns its result and then closes the manager.
 ///
@@ -46,14 +47,14 @@ public func withEvaluatorManager<T>(_ action: (EvaluatorManager) async throws ->
 }
 
 func getenv(_ key: String) -> String? {
-#if os(Windows)
+    #if os(Windows)
     let key = key.lowercased()
-    return ProcessInfo.processInfo.environment.first { (envKey: String, value: String) in
+    return ProcessInfo.processInfo.environment.first { (envKey: String, _: String) in
-        return key == envKey.lowercased()
+        key == envKey.lowercased()
     }?.value
-#else
+    #else
     return ProcessInfo.processInfo.environment[key]
-#endif
+    #endif
 }
 
 /// Resolve the (CLI) command to invoke Pkl.
@@ -108,7 +109,7 @@ public actor EvaluatorManager {
 
     // 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.
@@ -264,6 +265,9 @@ public actor EvaluatorManager {
         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(
@@ -371,8 +375,10 @@ enum PklBugError: Error {
 
 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
 
@@ -32,7 +32,9 @@ public struct EvaluatorOptions {
         logger: Logger = Loggers.noop,
         projectBaseURI: URL? = nil,
         http: Http? = nil,
-        declaredProjectDependencies: [String: ProjectDependency]? = nil
+        declaredProjectDependencies: [String: ProjectDependency]? = nil,
+        externalModuleReaders: [String: ExternalReader]? = nil,
+        externalResourceReaders: [String: ExternalReader]? = nil
     ) {
         self.allowedModules = allowedModules
         self.allowedResources = allowedResources
@@ -49,6 +51,8 @@ public struct EvaluatorOptions {
         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.
@@ -123,6 +127,18 @@ public struct EvaluatorOptions {
     /// 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 {
@@ -162,7 +178,9 @@ extension EvaluatorOptions {
             cacheDir: self.cacheDir,
             outputFormat: self.outputFormat,
             project: self.project(),
-            http: self.http
+            http: self.http,
+            externalModuleReaders: self.externalModuleReaders,
+            externalResourceReaders: self.externalResourceReaders
         )
     }
 
@@ -245,6 +263,8 @@ extension EvaluatorOptions {
         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
     }
 

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 EVALUATE_REQUEST = 0x23
-    case EVALUATOR_RESPONSE = 0x24
+    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_RESPONSE
+            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")
         }
@@ -123,6 +138,8 @@ struct CreateEvaluatorRequest: ClientRequestMessage {
     var outputFormat: String?
     var project: ProjectOrDependency?
     var http: Http?
+    var externalModuleReaders: [String: ExternalReader]?
+    var externalResourceReaders: [String: ExternalReader]?
 }
 
 struct ProjectOrDependency: Codable {
@@ -231,3 +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

@@ -1,18 +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
@@ -31,35 +31,104 @@ protocol MessageTransport {
 
 extension Pipe: Reader {
     public func read(into: UnsafeMutableRawBufferPointer) throws -> Int {
-        let data = try fileHandleForReading.read(upToCount: into.count)
+        try fileHandleForReading.read(into: into)
-        if data == nil {
-            return 0
-        }
-        data!.copyBytes(to: into)
-        return data!.count
     }
 
     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 {
+public class ServerMessageTransport: BaseMessageTransport {
-    var reader: Pipe!
-    var writer: Pipe!
-    var encoder: MessagePackEncoder!
-    var decoder: MessagePackDecoder!
     var process: Process?
     let pklCommand: [String]?
 
-    convenience init() {
+    override var running: Bool { self.process?.isRunning == true }
+
+    override convenience init() {
         self.init(pklCommand: nil)
     }
 
@@ -75,8 +144,8 @@ public class ChildProcessMessageTransport: MessageTransport {
         var arguments = Array(pklCommand.dropFirst())
         arguments.append("server")
         self.process!.arguments = arguments
-        self.reader = .init()
+        self.reader = Pipe()
-        self.writer = .init()
+        self.writer = Pipe()
         self.encoder = .init(writer: self.writer)
         self.decoder = .init(reader: self.reader)
         self.process!.standardOutput = self.reader
@@ -85,17 +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)")
+        try super.send(message)
-
-        let messageType = MessageType.getMessageType(message)
-        try self.encoder.encodeArrayHeader(2)
-        try self.encoder.encode(messageType)
-        try self.encoder.encode(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
         }
@@ -111,45 +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:
+        case MessageType.INITIALIZE_MODULE_READER_REQUEST:
-            return try self.decoder.decode(as: CreateEvaluatorResponse.self)
+            return try self.decoder.decode(as: InitializeModuleReaderRequest.self)
-        case MessageType.EVALUATOR_RESPONSE:
+        case MessageType.INITIALIZE_RESOURCE_READER_REQUEST:
-            return try self.decoder.decode(as: EvaluateResponse.self)
+            return try self.decoder.decode(as: InitializeResourceReaderRequest.self)
-        case MessageType.READ_MODULE_REQUEST:
+        case MessageType.CLOSE_EXTERNAL_PROCESS:
-            return try self.decoder.decode(as: ReadModuleRequest.self)
+            return try self.decoder.decode(as: CloseExternalProcess.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)
         default:
-            fatalError("Unreachable code")
+            return try super.decodeMessage(messageType)
         }
     }
 
-    func getMessages() throws -> AsyncThrowingStream<ServerMessage, Error> {
+    override func close() {
-        try self.ensureProcessStarted()
+        self._running = false
-        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()
-            }
-        }
     }
 }

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
 

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

@@ -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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 /// The Swift representation of standard library module `pkl.EvaluatorSettings`.
 public struct PklEvaluatorSettings: Decodable, Hashable {
@@ -26,6 +26,28 @@ public struct PklEvaluatorSettings: Decodable, Hashable {
     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.
@@ -85,3 +107,8 @@ public struct Proxy: Codable, Hashable {
     /// ```
     var noProxy: [String]?
 }
+
+public struct ExternalReader: Codable, Hashable {
+    var executable: String
+    var arguments: [String]? = nil
+}

Sources/PklSwift/Project.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 /// The Swift representation of `pkl.Project`
 public struct Project: PklRegisteredType, Hashable, DependencyDeclaredInProjectFile {

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
+    /// The first URI conveys name "swallow.pkl" within parent "/catalog/". The second URI
-    /// conveys the name "persons/fred.pkl" with no hierarchical meaning.
+    /// 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

@@ -1,18 +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
 
@@ -85,3 +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 © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
-//
+ *
-// Copyright (c) 2024 Apple Inc. and the Swift project authors
+ * Licensed under the Apache License, Version 2.0 (the "License");
-// Licensed under Apache License v2.0 with Runtime Library Exception
+ * you may not use this file except in compliance with the License.
-//
+ * You may obtain a copy of the License at
-// See https://swift.org/LICENSE.txt for license information
+ *
-// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+ *   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 © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
-//
+ *
-// Copyright (c) 2024 Apple Inc. and the Swift project authors
+ * Licensed under the Apache License, Version 2.0 (the "License");
-// Licensed under Apache License v2.0 with Runtime Library Exception
+ * you may not use this file except in compliance with the License.
-//
+ * You may obtain a copy of the License at
-// See https://swift.org/LICENSE.txt for license information
+ *
-// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+ *   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 © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
-//
+ *
-// Copyright (c) 2024 Apple Inc. and the Swift project authors
+ * Licensed under the Apache License, Version 2.0 (the "License");
-// Licensed under Apache License v2.0 with Runtime Library Exception
+ * you may not use this file except in compliance with the License.
-//
+ * You may obtain a copy of the License at
-// See https://swift.org/LICENSE.txt for license information
+ *
-// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+ *   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/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

@@ -1,18 +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 SemanticVersion
 import XCTest

Tests/PklSwiftTests/EvaluatorTest.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
 
 @testable import MessagePack
 @testable import PklSwift
@@ -305,10 +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/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
+            let container = try decoder.singleValueContainer()
-            switch decoded {
+            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
+            let container = try decoder.singleValueContainer()
-            switch decoded {
+            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
+            let container = try decoder.singleValueContainer()
-            switch decoded {
+            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))"
                     )
                 )
             }
@@ -107,6 +113,114 @@ 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 let registeredIdentifier: String = "UnionTypes"
 
@@ -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
@@ -156,6 +300,16 @@ 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
         }
     }
 
@@ -191,6 +345,18 @@ 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 let registeredIdentifier: String = "UnionTypes#Zebra"
 

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
@@ -160,7 +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

@@ -1,18 +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 SemanticVersion
 import XCTest
@@ -22,12 +22,13 @@ import XCTest
 class ProjectTest: XCTestCase {
     func testLoadProject() async throws {
         let version = try await SemanticVersion(EvaluatorManager().getVersion())!
-        let tempDir = NSTemporaryDirectory()
+        let tempDir = try tempDir()
-        try FileManager.default.createDirectory(atPath: tempDir + "/subdir", withIntermediateDirectories: true)
+        let subDir = tempDir.appendingPathComponent("subdir")
-        let otherProjectFile = URL(fileURLWithPath: tempDir, isDirectory: true)
+        try FileManager.default.createDirectory(at: subDir, withIntermediateDirectories: true)
-            .appendingPathComponent("subdir/PklProject")
+        let otherProjectFile = subDir.appendingPathComponent("PklProject")
 
         try #"""
+        @ModuleInfo { minPklVersion = "0.25.0" }
         amends "pkl:Project"
 
         package {
@@ -38,8 +39,8 @@ class ProjectTest: XCTestCase {
         }
         """#.write(to: otherProjectFile, atomically: true, encoding: .utf8)
 
-        let file = URL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true)
+        let file = try (PklSwift.tempDir()).appendingPathComponent("PklProject")
-            .appendingPathComponent("PklProject")
+
         let httpSetting = version < pklVersion0_26 ? "" : """
         http {
           proxy {
@@ -51,10 +52,40 @@ class ProjectTest: XCTestCase {
           }
         }
         """
+        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"
 
@@ -99,7 +130,9 @@ class ProjectTest: XCTestCase {
           timeout = 5.min
           moduleCacheDir = "/bar/buzz"
           rootDir = "/buzzy"
+          \#(externalReaderSettings)
           \#(httpSetting)
+          \#(colorSetting)
         }
 
         dependencies {
@@ -124,7 +157,10 @@ class ProjectTest: XCTestCase {
                 timeout: .minutes(5),
                 moduleCacheDir: "/bar/buzz",
                 rootDir: "/buzzy",
-                http: httpExpectation
+                http: httpExpectation,
+                externalModuleReaders: externalModuleReadersExpectation,
+                externalResourceReaders: externalResourceReadersExpectation,
+                color: color
             )
             let expectedPackage = PklSwift.Project.Package(
                 name: "hawk",
@@ -179,7 +215,10 @@ class ProjectTest: XCTestCase {
                         timeout: nil,
                         moduleCacheDir: nil,
                         rootDir: nil,
-                        http: nil
+                        http: nil,
+                        externalModuleReaders: nil,
+                        externalResourceReaders: nil,
+                        color: nil
                     ),
                     projectFileUri: "\(otherProjectFile)",
                     tests: [],

VERSION.txt

@@ -1 +1 @@
-0.3.0
+0.4.2

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
+            let container = try decoder.singleValueContainer()
-            switch decoded {
+            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
+            let container = try decoder.singleValueContainer()
-            switch decoded {
+            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
+            let container = try decoder.singleValueContainer()
-            switch decoded {
+            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
+            let container = try decoder.singleValueContainer()
-            switch decoded {
+            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))"
                     )
                 )
             }

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

@@ -4,7 +4,7 @@ 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"
     }

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

@@ -4,7 +4,7 @@ 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"

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"

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": {}
-}
+}

codegen/src/internal/ClassGen.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 module pkl.swift.internal.ClassGen
 

codegen/src/internal/EnumGen.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 module pkl.swift.internal.EnumGen
 
@@ -57,6 +58,10 @@ local enumNormalMembers = enumBaseMembers.map((it) -> (it) {
       else baseName
 })
 
+local enumNonNumericMembers = enumNormalMembers.filter((it) -> !it.type.isNumeric)
+
+local enumNumericMembers = enumNormalMembers.filter((it) -> it.type.isNumeric)
+
 contents =
   if (isStringLiteralUnion) stringLiteralEnumContents
   else enumContents
@@ -66,7 +71,7 @@ local stringLiteralEnumContents =
     when (alias.docComment != null) {
       utils.renderDocComment(alias.docComment!!, "")
     }
-    "public enum \(module.mapping.name): String, CaseIterable, Decodable, Hashable {"
+    "public enum \(module.mapping.name): String, CaseIterable, CodingKeyRepresentable, Decodable, Hashable {"
     for (member in enumStringLiteralMembers) {
       "\(module.indent)case \(member.name) = \(utils.toSwiftString((member.pklType as reflect.StringLiteralType).value))"
     }
@@ -79,33 +84,19 @@ local enumContents =
       utils.renderDocComment(alias.docComment!!, "")
     }
     "public enum \(module.mapping.name): Decodable, Hashable {"
-    for (member in enumNormalMembers) {
+    for (member: EnumMember in enumNormalMembers) {
       "\(module.indent)case \(member.name)(\(member.renderedType))"
     }
     ""
+    when (!enumNumericMembers.isEmpty) {
+      decodeNumeric
+      ""
+    }
     when (enumNormalMembers.any((it) -> it.type.isPolymorphic)) {
       synthesizedEquals
       ""
     }
-    "\(module.indent)public init(from decoder: Decoder) throws {"
+    initMethod
-    "\(module.indent.repeat(2))let decoded = try decoder.singleValueContainer().decode(PklSwift.PklAny.self).value"
-    "\(module.indent.repeat(2))switch decoded {"
-    for (member in enumNormalMembers) {
-      "\(module.indent.repeat(2))case let decoded as \(member.renderedType):"
-      "\(module.indent.repeat(3))self = \(module.mapping.name).\(member.name)(decoded)"
-    }
-    """
-    \(module.indent.repeat(2))default:
-    \(module.indent.repeat(3))throw DecodingError.typeMismatch(
-    \(module.indent.repeat(4))\(module.mapping.name).self,
-    \(module.indent.repeat(4)).init(
-    \(module.indent.repeat(5))codingPath: decoder.codingPath,
-    \(module.indent.repeat(5))debugDescription: "Expected type \(module.mapping.name), but got \\(String(describing: decoded))"
-    \(module.indent.repeat(4)))
-    \(module.indent.repeat(3)))
-    \(module.indent.repeat(2))}
-    \(module.indent)}
-    """
     when (enumNormalMembers.any((it) -> it.type.isPolymorphic)) {
       ""
       synthesizedHash
@@ -113,6 +104,44 @@ local enumContents =
     "}"
   }.join("\n")
 
+local throwTypeMismatch = new Listing {
+  "\(module.indent.repeat(2))throw DecodingError.typeMismatch("
+  "\(module.indent.repeat(3))\(module.mapping.name).self,"
+  "\(module.indent.repeat(3)).init("
+  "\(module.indent.repeat(4))codingPath: decoder.codingPath,"
+  "\(module.indent.repeat(4))debugDescription: \"Expected type \(module.mapping.name), but got \\(String(describing: value))\""
+  "\(module.indent.repeat(3)))"
+  "\(module.indent.repeat(2)))"
+}.join("\n")
+
+local initMethod = new Listing {
+  "\(module.indent)public init(from decoder: Decoder) throws {"
+  "\(module.indent.repeat(2))let container = try decoder.singleValueContainer()"
+  when (!enumNumericMembers.isEmpty) {
+    "\(module.indent.repeat(2))let decoded = \(module.mapping.name).decodeNumeric(from: decoder, container)"
+    "\(module.indent.repeat(2))if decoded != nil {"
+    "\(module.indent.repeat(3))self = decoded!"
+    "\(module.indent.repeat(3))return"
+    "\(module.indent.repeat(2))}"
+  }
+  "\(module.indent.repeat(2))let value = try container.decode(PklSwift.PklAny.self).value"
+  when (!enumNonNumericMembers.isEmpty) {
+    "\(module.indent.repeat(2))switch value?.base {"
+    for (member in enumNonNumericMembers) {
+      "\(module.indent.repeat(2))case let decoded as \(member.renderedType):"
+      "\(module.indent.repeat(3))self = \(module.mapping.name).\(member.name)(decoded)"
+    }
+    "\(module.indent.repeat(2))default:"
+    // indent one more level
+    module.indent + throwTypeMismatch.split("\n").join("\n" + module.indent)
+    "\(module.indent.repeat(2))}"
+  } else {
+    throwTypeMismatch
+  }
+  "\(module.indent)}"
+}
+  .join("\n")
+
 local synthesizedEquals = new Listing {
   "\(module.indent)public static func ==(lhs: \(module.mapping.name), rhs: \(module.mapping.name)) -> Bool {"
   "\(module.indent.repeat(2))switch (lhs, rhs) {"
@@ -141,6 +170,23 @@ local synthesizedHash = new Listing {
   "\(module.indent)}"
 }.join("\n")
 
+local decodeNumeric = new Listing {
+  "\(module.indent)private static func decodeNumeric(from decoder: Decoder, _ container: any SingleValueDecodingContainer) -> \(module.mapping.name)? {"
+  when (enumNumericMembers.length == 1) {
+    local member = enumNumericMembers.first
+    "\(module.indent.repeat(2))return try? .\(member.name)(container.decode(\(member.renderedType).self))"
+  } else {
+    for (idx, member in enumNumericMembers) {
+      when (idx == 0) {
+        "\(module.indent.repeat(2))return (try? .\(member.name)(container.decode(\(member.renderedType).self)))"
+      } else {
+        "\(module.indent.repeat(3))?? (try? .\(member.name)(container.decode(\(member.renderedType).self)))"
+      }
+    }
+  }
+  "\(module.indent)}"
+}.join("\n")
+
 local class EnumMember {
   name: String
   type: Type

codegen/src/internal/Gen.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 abstract module pkl.swift.internal.Gen
 

codegen/src/internal/SwiftMapping.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 abstract module pkl.swift.internal.SwiftMapping
 

codegen/src/internal/SwiftNamespace.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 module pkl.swift.internal.SwiftNamespace
 

codegen/src/internal/Type.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 /// Representation of a type in Swift.
 @Unlisted
 abstract module pkl.swift.internal.Type
@@ -28,6 +29,9 @@ isPolymorphic: Boolean = false
 /// True if this type represents a Pkl Any
 isAny: Boolean = false
 
+/// Tells if this type represents a number (int or float) or not
+isNumeric: Boolean = false
+
 /// Renders this type into source code.
 ///
 /// [swiftModuleName] is the full path of the package that this type appears in.

codegen/src/internal/TypeAliasGen.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 module pkl.swift.internal.TypeAliasGen
 

codegen/src/internal/gatherer.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 module pkl.swift.internal.gatherer
 

codegen/src/internal/typegen.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 /// Utilities for generating Swift types from Pkl.
 @Unlisted
 module pkl.swift.internal.typegen
@@ -76,16 +77,16 @@ anyType: Type.Nullable = new { elem = builtInType("AnyHashable") }
 local neverType: Type.Declared = builtInType("Never")
 
 mappedTypes: Mapping<Class|TypeAlias, Type> = new {
-  [Int] = new Type.Declared { typeName = "Int" }
+  [Int] = new Type.Declared { typeName = "Int"; isNumeric = true }
-  [Int8] = new Type.Declared { typeName = "Int8" }
+  [Int8] = new Type.Declared { typeName = "Int8"; isNumeric = true  }
-  [Int16] = new Type.Declared { typeName = "Int16" }
+  [Int16] = new Type.Declared { typeName = "Int16"; isNumeric = true  }
-  [Int32] = new Type.Declared { typeName = "Int32" }
+  [Int32] = new Type.Declared { typeName = "Int32"; isNumeric = true  }
-  [UInt] = new Type.Declared { typeName = "UInt" }
+  [UInt] = new Type.Declared { typeName = "UInt"; isNumeric = true  }
-  [UInt8] = new Type.Declared { typeName = "UInt8" }
+  [UInt8] = new Type.Declared { typeName = "UInt8"; isNumeric = true  }
-  [UInt16] = new Type.Declared { typeName = "UInt16" }
+  [UInt16] = new Type.Declared { typeName = "UInt16"; isNumeric = true  }
-  [UInt32] = new Type.Declared { typeName = "UInt32" }
+  [UInt32] = new Type.Declared { typeName = "UInt32"; isNumeric = true  }
-  [Number] = new Type.Declared { typeName = "Float64" }
+  [Number] = new Type.Declared { typeName = "Float64"; isNumeric = true  }
-  [Float] = new Type.Declared { typeName = "Float64" }
+  [Float] = new Type.Declared { typeName = "Float64"; isNumeric = true  }
   [String] = new Type.Declared { typeName = "String" }
   [Boolean] = new Type.Declared { typeName = "Bool" }
   [Null] = new Type.Declared { typeName = "Optional"; typeArguments = List(neverType) }

codegen/src/internal/utils.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Unlisted
 module pkl.swift.internal.utils
 

codegen/src/swift.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 @Module { name = "pkl_gen_swift" }
 module pkl.swift.swift
 

codegen/src/tests/ClassGen.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 amends "pkl:test"
 
 import ".../internal/ClassGen.pkl"

codegen/src/tests/fixtures/types.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 class Bike {
   isFixie: Boolean
 }

codegen/src/tests/fixtures/types2.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 import "types3.pkl"
 
 class Person {

codegen/src/tests/fixtures/types3.pkl

@@ -1,16 +1,17 @@
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
-// 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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 class Bike

codegen/src/tests/fixtures/types4.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 class Foo {
   bar: Listing<Int|String>
 }

codegen/src/tests/gatherer.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 amends "pkl:test"
 
 import "pkl:reflect"

codegen/src/tests/typegen.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 amends "pkl:test"
 
 import "pkl:reflect"

codegen/src/tests/utils.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.
-// ===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
 amends "pkl:test"
 
 import "../internal/utils.pkl"

docs/antora.yml

@@ -1,5 +1,5 @@
 name: swift
 title: Pkl Swift Bindings
-version: 0.3.0
+version: 0.4.2
 nav:
   - nav.adoc

docs/modules/ROOT/pages/CHANGELOG.adoc

@@ -1,5 +1,46 @@
 = Changelog
 
+[[release-0.4.2]]
+== 0.4.2 (2025-04-14)
+
+=== Fixes
+
+* Fixes an issue where enum keys fail to be decoded (https://github.com/apple/pkl-swift/pull/45[#45]).
+* Fixes an issue where unions of ints can possibly be decoded incorrectly (https://github.com/apple/pkl-swift/pull/47[#47]).
+
+=== Miscellaneous
+
+* Auto-generate DocC documentation in the Swift Package Index (https://github.com/apple/pkl-swift/pull/41[#41]).
+* Update license headers (https://github.com/apple/pkl-swift/pull/43[#43]).
+
+[[release-0.4.1]]
+== 0.4.1 (2025-02-04)
+
+=== Fixes
+
+* Fixes an issue where union types might get decoded as the wrong Swift type (https://github.com/apple/pkl-swift/pull/39[#39]).
+
+[[release-0.4.0]]
+== 0.4.0 (2025-01-24)
+
+=== Additions
+
+* Add a new API for creating external readers, called `ExternalReaderClient` (https://github.com/apple/pkl-swift/pull/26[#26]).
+* Add new fields to support new options available in Pkl 0.27 (https://github.com/apple/pkl-swift/pull/26[#26], https://github.com/apple/pkl-swift/pull/32[#32]):
+    - In struct `EvaluatorOptions`: `externalModuleReaders` and `externalResourceReaders`.
+    - In struct `PklEvaluatorSettings`: `externalModuleReaders`, `externalResourceReaders`, and `color`.
+
+=== Changes
+
+* Make `PathElement.init` public (https://github.com/apple/pkl-swift/pull/31[#31]).
+
+=== Contributors ❤️
+
+Thank you to all our contributors!
+
+* https://github.com/HT154[@HT154]
+* https://github.com/jcubit[@jcubit]
+
 [[release-0.3.0]]
 == 0.3.0 (2024-10-10)
 

docs/modules/ROOT/pages/external-readers.adoc

@@ -0,0 +1,37 @@
+= External Readers
+
+pkl-swift provides APIs that aid in implementing xref:main:language-reference:index.adoc#external-readers[External Readers].
+In this mode of execution, the program built with pkl-swift runs as a child process of the Pkl evaluator, rather than a parent process.
+The `PklSwift.ExternalReaderClient` type provides a set of tools for building external readers.
+
+Much like implementing xref:ROOT:evaluation.adoc#custom-readers[Custom Readers], external readers are implemented by providing one or more instances of the `PklSwift.ResourceReader` and `pkl.ModuleReader` protocols.
+
+== Example
+
+.main.swift
+[source,swift]
+----
+import Foundation
+import PklSwift
+
+@main struct Main {
+    static func main() async throws {
+        let client = ExternalReaderClient(
+            options: ExternalReaderClientOptions(
+                resourceReaders: [MyResourceReader()]
+            ))
+        try await client.run()
+    }
+}
+
+struct MyResourceReader: ResourceReader {
+    var scheme: String { "env2" }
+    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(scheme.count + 1)
+        return Array((ProcessInfo.processInfo.environment[String(key)] ?? "").utf8)
+    }
+}
+----

docs/nav.adoc

@@ -1,4 +1,5 @@
 * xref:ROOT:quickstart.adoc[Quickstart]
 * xref:ROOT:evaluation.adoc[Evaluator API]
 * xref:ROOT:codegen.adoc[Code Generation]
+* xref:ROOT:external-readers.adoc[External Readers]
 * xref:ROOT:CHANGELOG.adoc[Changelog]

generator-settings.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.
+//===----------------------------------------------------------------------===//
+
 amends "codegen/src/GeneratorSettings.pkl"
 
 generateScript = "codegen/src/Generator.pkl"

licenserc.toml

@@ -0,0 +1,29 @@
+additionalHeaders = ["scripts/pkl-header-style.toml"]
+
+headerPath = "scripts/license-header.txt"
+
+includes = [
+    "*.swift",
+    "*.pkl",
+    "*.h",
+    "*.cpp",
+    "*.sh",
+    "PklProject",
+]
+
+excludes = [
+    "Sources/pkl-gen-swift/Generated",
+    "Tests/PklSwiftTests/Fixtures",
+    "codegen/snippet-tests",
+    "doc",
+]
+
+[git]
+attrs = 'enable'
+ignore = 'enable'
+
+[properties]
+copyrightOwner = "Apple Inc. and the Pkl project authors"
+
+[mapping.SWIFT_STYLE]
+extensions = ["swift"]

scripts/license-header.txt

@@ -0,0 +1,13 @@
+Copyright ©{{ " " }}{%- if attrs.git_file_modified_year != attrs.git_file_created_year -%}{{ attrs.git_file_created_year }}-{{ attrs.git_file_modified_year }}{%- else -%}{{ attrs.git_file_created_year }}{%- endif -%}{{ " " }}{{ props["copyrightOwner"] }}. 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.

scripts/pkl-header-style.toml

@@ -0,0 +1,11 @@
+[SWIFT_STYLE]
+firstLine = '//===----------------------------------------------------------------------===//'
+endLine = "//===----------------------------------------------------------------------===//\n"
+beforeEachLine = '// '
+afterEachLine = ''
+allowBlankLines = false
+multipleLines = true
+padLines = false
+firstLineDetectionPattern = '//\s?==='
+lastLineDetectionPattern = '//\s?==='
+skipLinePattern = '// swift-tools-version'