Add optional return_value_from_void_function rule using SwiftSyntax (#3054)

* Add optional return_value_from_void_function rule using SwiftSyntax

* Use Script/bootstrap in CI

* Make SwiftSyntax optional

* Make SwiftSyntax optional in SPM

* Fix Package.swift

* Try again

* Add minSwiftVersion

* Fix thread sanitizer issue

* Take 2

* Fix false positive on nested computed variables

* Remove support for Xcode 10.x

* Fix rule description

* Enable opt-in rule in configuration file

* Extract code into `SyntaxRule` protocol

* nit: make property private

* Missing docs

* Fix MasterRuleList.swift

* Update CHANGELOG

* Remove unused imports

* Use Example type

* Change rule kind to .idiomatic

* Update CHANGELOG

* Bump deployment target to macOS 10.12

* Simplify SyntaxRule.validate(file:visitor)

* Make TSan happy

* Use script/bootstrap in the README

.gitmodules

@@ -16,3 +16,6 @@
 [submodule "Carthage/Checkouts/Yams"]
 	path = Carthage/Checkouts/Yams
 	url = https://github.com/jpsim/Yams.git
+[submodule "SwiftSyntax"]
+	path = SwiftSyntax
+	url = https://github.com/apple/swift-syntax.git

.swiftlint.yml

@@ -54,6 +54,7 @@ opt_in_rules:
   - reduce_into
   - redundant_nil_coalescing
   - redundant_type_annotation
+  - return_value_from_void_function
   - single_test_class
   - sorted_first_last
   - sorted_imports

CHANGELOG.md

@@ -9,6 +9,10 @@
   [Paul Taykalo](https://github.com/PaulTaykalo)
   [JP Simard](https://github.com/jpsim)
 
+* SwiftLint now imports [SwiftSyntax](https://github.com/apple/swift-syntax)
+  and requires Xcode 11.0 to build.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+
 #### Experimental
 
 * None.
@@ -26,6 +30,14 @@
   [ZevEisenberg](https://github.com/ZevEisenberg)
   [#3040](https://github.com/realm/SwiftLint/pull/3040)
 
+* Introduce a new `SyntaxRule` that enables writing rules using
+  [SwiftSyntax](https://github.com/apple/swift-syntax).  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+
+* Add `return_value_from_void_function` opt-in rule to warn against using
+  `return <expression>` in a function that is `Void`.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+
 #### Bug Fixes
 
 * Fix `discarded_notification_center_observer` false positives when

Package.resolved

@@ -55,6 +55,15 @@
           "version": "0.29.0"
         }
       },
+      {
+        "package": "SwiftSyntax",
+        "repositoryURL": "https://github.com/apple/swift-syntax.git",
+        "state": {
+          "branch": null,
+          "revision": "3e3eb191fcdbecc6031522660c4ed6ce25282c25",
+          "version": "0.50100.0"
+        }
+      },
       {
         "package": "SwiftyTextTable",
         "repositoryURL": "https://github.com/scottrhoyt/SwiftyTextTable.git",

Package.swift

@@ -7,8 +7,17 @@ private let addCryptoSwift = false
 private let addCryptoSwift = true
 #endif
 
+#if compiler(>=5.1.0)
+private let addSwiftSyntax = true
+#else
+private let addSwiftSyntax = false
+#endif
+
 let package = Package(
     name: "SwiftLint",
+    platforms: [
+       .macOS(.v10_12)
+    ],
     products: [
         .executable(name: "swiftlint", targets: ["swiftlint"]),
         .library(name: "SwiftLintFramework", targets: ["SwiftLintFramework"])
@@ -18,7 +27,8 @@ let package = Package(
         .package(url: "https://github.com/jpsim/SourceKitten.git", .upToNextMinor(from: "0.29.0")),
         .package(url: "https://github.com/jpsim/Yams.git", from: "2.0.0"),
         .package(url: "https://github.com/scottrhoyt/SwiftyTextTable.git", from: "0.9.0"),
-    ] + (addCryptoSwift ? [.package(url: "https://github.com/krzyzanowskim/CryptoSwift.git", .upToNextMinor(from: "1.0.0"))] : []),
+    ] + (addCryptoSwift ? [.package(url: "https://github.com/krzyzanowskim/CryptoSwift.git", .upToNextMinor(from: "1.0.0"))] : []) +
+        (addSwiftSyntax ? [.package(url: "https://github.com/apple/swift-syntax.git", .exact("0.50100.0"))] : []),
     targets: [
         .target(
             name: "swiftlint",
@@ -33,7 +43,8 @@ let package = Package(
             dependencies: [
                 "SourceKittenFramework",
                 "Yams",
-            ] + (addCryptoSwift ? ["CryptoSwift"] : [])
+            ] + (addCryptoSwift ? ["CryptoSwift"] : []) +
+                (addSwiftSyntax ? ["SwiftSyntax"] : [])
         ),
         .testTarget(
             name: "SwiftLintFrameworkTests",

README.md

@@ -61,7 +61,7 @@ running it.
 ### Compiling from source:
 
 You can also build from source by cloning this project and running
-`git submodule update --init --recursive; make install` (Xcode 10.2 or later).
+`script/bootstrap; make install` (Xcode 11.0 or later).
 
 ### Known Installation Issues On MacOS Before 10.14.4
 

Source/SwiftLintFramework/Extensions/SwiftLintFile+Cache.swift

@@ -1,5 +1,8 @@
 import Foundation
 import SourceKittenFramework
+#if canImport(SwiftSyntax)
+import SwiftSyntax
+#endif
 
 private typealias FileCacheKey = Int
 private var responseCache = Cache({ file -> [String: SourceKitRepresentable]? in
@@ -30,6 +33,20 @@ private var syntaxMapCache = Cache({ file in
 private var syntaxKindsByLinesCache = Cache({ file in file.syntaxKindsByLine() })
 private var syntaxTokensByLinesCache = Cache({ file in file.syntaxTokensByLine() })
 
+#if canImport(SwiftSyntax)
+private var syntaxCache = Cache({ file -> SourceFileSyntax? in
+    do {
+        if let path = file.path {
+            return try SyntaxParser.parse(URL(fileURLWithPath: path))
+        }
+
+         return try SyntaxParser.parse(source: file.contents)
+    } catch {
+        return nil
+    }
+})
+#endif
+
 internal typealias AssertHandler = () -> Void
 
 private var assertHandlers = [FileCacheKey: AssertHandler]()
@@ -158,6 +175,19 @@ extension SwiftLintFile {
         return syntaxMap
     }
 
+    #if canImport(SwiftSyntax)
+    internal var syntax: SourceFileSyntax {
+        guard let syntax = syntaxCache.get(self) else {
+            if let handler = assertHandler {
+                handler()
+                return SourceFileSyntax({ _ in })
+            }
+            queuedFatalError("Never call this for file that sourcekitd fails.")
+        }
+        return syntax
+    }
+    #endif
+
     internal var syntaxTokensByLines: [[SwiftLintSyntaxToken]] {
         guard let syntaxTokensByLines = syntaxTokensByLinesCache.get(self) else {
             if let handler = assertHandler {
@@ -189,6 +219,9 @@ extension SwiftLintFile {
         syntaxMapCache.invalidate(self)
         syntaxTokensByLinesCache.invalidate(self)
         syntaxKindsByLinesCache.invalidate(self)
+        #if canImport(SwiftSyntax)
+        syntaxCache.invalidate(self)
+        #endif
     }
 
     internal static func clearCaches() {
@@ -200,5 +233,8 @@ extension SwiftLintFile {
         syntaxMapCache.clear()
         syntaxTokensByLinesCache.clear()
         syntaxKindsByLinesCache.clear()
+        #if canImport(SwiftSyntax)
+        syntaxCache.clear()
+        #endif
     }
 }

Source/SwiftLintFramework/Models/MasterRuleList.swift

@@ -147,6 +147,7 @@ public let masterRuleList = RuleList(rules: [
     RequiredDeinitRule.self,
     RequiredEnumCaseRule.self,
     ReturnArrowWhitespaceRule.self,
+    ReturnValueFromVoidFunctionRule.self,
     ShorthandOperatorRule.self,
     SingleTestClassRule.self,
     SortedFirstLastRule.self,

Source/SwiftLintFramework/Protocols/SyntaxRule.swift

@@ -0,0 +1,44 @@
+import Foundation
+#if canImport(SwiftSyntax)
+import SwiftSyntax
+#endif
+
+/// A rule that leverages the SwiftSyntax library.
+public protocol SyntaxRule: Rule {}
+
+#if canImport(SwiftSyntax)
+/// A SwiftSyntax visitor that collects data to provide violations for a specific rule.
+public protocol SyntaxRuleVisitor: SyntaxVisitor {
+    /// The rule that uses this visitor.
+    associatedtype Rule: SyntaxRule
+
+    /// Returns the violations that should be calculated based on data that was accumulated during the `visit` methods.
+    func violations(for rule: Rule, in file: SwiftLintFile) -> [StyleViolation]
+}
+
+public extension SyntaxRule {
+    /// Wraps computation of violations based on a visitor.
+    func validate<Visitor: SyntaxRuleVisitor>(file: SwiftLintFile,
+                                              visitor: Visitor) -> [StyleViolation] where Visitor.Rule == Self {
+        let lock = NSLock()
+        var visitor = visitor
+
+        // https://bugs.swift.org/browse/SR-11170
+        let work = DispatchWorkItem {
+            lock.lock()
+            file.syntax.walk(&visitor)
+            lock.unlock()
+        }
+        let thread = Thread {
+            work.perform()
+        }
+        thread.stackSize = 8 << 20 // 8 MB.
+        thread.start()
+        work.wait()
+
+        lock.lock()
+        defer { lock.unlock() }
+        return visitor.violations(for: self, in: file)
+    }
+}
+#endif

Source/SwiftLintFramework/Rules/Idiomatic/ReturnValueFromVoidFunctionRule.swift

@@ -0,0 +1,76 @@
+import SourceKittenFramework
+#if canImport(SwiftSyntax)
+import SwiftSyntax
+#endif
+
+public struct ReturnValueFromVoidFunctionRule: ConfigurationProviderRule, SyntaxRule, OptInRule,
+                                               AutomaticTestableRule {
+    public var configuration = SeverityConfiguration(.warning)
+
+    public init() {}
+
+    public static let description = RuleDescription(
+        identifier: "return_value_from_void_function",
+        name: "Return Value from Void Function",
+        description: "Returning values from Void functions should be avoided.",
+        kind: .idiomatic,
+        minSwiftVersion: .fiveDotOne,
+        nonTriggeringExamples: ReturnValueFromVoidFunctionRuleExamples.nonTriggeringExamples,
+        triggeringExamples: ReturnValueFromVoidFunctionRuleExamples.triggeringExamples
+    )
+
+    public func validate(file: SwiftLintFile) -> [StyleViolation] {
+        #if canImport(SwiftSyntax)
+        return validate(file: file, visitor: ReturnVisitor())
+        #else
+        return []
+        #endif
+    }
+}
+
+#if canImport(SwiftSyntax)
+private class ReturnVisitor: SyntaxRuleVisitor {
+    private var positions = [AbsolutePosition]()
+
+    func visit(_ node: ReturnStmtSyntax) -> SyntaxVisitorContinueKind {
+        if node.expression != nil,
+            let functionNode = node.enclosingFunction(),
+            functionNode.returnsVoid {
+            positions.append(node.positionAfterSkippingLeadingTrivia)
+        }
+        return .visitChildren
+    }
+
+    func violations(for rule: ReturnValueFromVoidFunctionRule, in file: SwiftLintFile) -> [StyleViolation] {
+        return positions.map { position in
+            StyleViolation(ruleDescription: type(of: rule).description,
+                           severity: rule.configuration.severity,
+                           location: Location(file: file, byteOffset: ByteCount(position.utf8Offset)))
+        }
+    }
+}
+
+private extension Syntax {
+    func enclosingFunction() -> FunctionDeclSyntax? {
+        if let node = self as? FunctionDeclSyntax {
+            return node
+        }
+
+        if self is ClosureExprSyntax || self is VariableDeclSyntax {
+            return nil
+        }
+
+        return parent?.enclosingFunction()
+    }
+}
+
+private extension FunctionDeclSyntax {
+    var returnsVoid: Bool {
+        if let type = signature.output?.returnType as? SimpleTypeIdentifierSyntax {
+            return type.name.text == "Void"
+        }
+
+        return signature.output?.returnType == nil
+    }
+}
+#endif

Source/SwiftLintFramework/Rules/Idiomatic/ReturnValueFromVoidFunctionRuleExamples.swift

@@ -0,0 +1,234 @@
+// swiftlint:disable:next type_body_length
+internal struct ReturnValueFromVoidFunctionRuleExamples {
+    static let nonTriggeringExamples = [
+        Example("""
+        func foo() {
+            return
+        }
+        """),
+        Example("""
+        func foo() {
+            return /* a comment */
+        }
+        """),
+        Example("""
+        func foo() -> Int {
+            return 1
+        }
+        """),
+        Example("""
+        func foo() -> Void {
+            if condition {
+                return
+            }
+            bar()
+        }
+        """),
+        Example("""
+        func foo() {
+            return;
+            bar()
+        }
+        """),
+        Example("func test() {}"),
+        Example("""
+        init?() {
+            guard condition else {
+                return nil
+            }
+        }
+        """),
+        Example("""
+        init?(arg: String?) {
+            guard arg != nil else {
+                return nil
+            }
+        }
+        """),
+        Example("""
+        func test() {
+            guard condition else {
+                return
+            }
+        }
+        """),
+        Example("""
+        func test() -> Result<String, Error> {
+            func other() {}
+            func otherVoid() -> Void {}
+        }
+        """),
+        Example("""
+        func test() -> Int? {
+            return nil
+        }
+        """),
+        Example("""
+        func test() {
+            if bar {
+                print("")
+                return
+            }
+            let foo = [1, 2, 3].filter { return true }
+            return
+        }
+        """),
+        Example("""
+        func test() {
+            guard foo else {
+                bar()
+                return
+            }
+        }
+        """),
+        Example("""
+        func spec() {
+            var foo: Int {
+                return 0
+            }
+        """)
+    ]
+
+    static let triggeringExamples = [
+        Example("""
+        func foo() {
+            ↓return bar()
+        }
+        """),
+        Example("""
+        func foo() {
+            ↓return self.bar()
+        }
+        """),
+        Example("""
+        func foo() -> Void {
+            ↓return bar()
+        }
+        """),
+        Example("""
+        func foo() -> Void {
+            ↓return /* comment */ bar()
+        }
+        """),
+        Example("""
+        func foo() {
+            ↓return
+            self.bar()
+        }
+        """),
+        Example("""
+        func foo() {
+            variable += 1
+            ↓return
+            variable += 1
+        }
+        """),
+        Example("""
+        func initThing() {
+            guard foo else {
+                ↓return print("")
+            }
+        }
+        """),
+        Example("""
+        // Leading comment
+        func test() {
+            guard condition else {
+                ↓return assertionfailure("")
+            }
+        }
+        """),
+        Example("""
+        func test() -> Result<String, Error> {
+            func other() {
+                guard false else {
+                    ↓return assertionfailure("")
+                }
+            }
+            func otherVoid() -> Void {}
+        }
+        """),
+        Example("""
+        func test() {
+            guard conditionIsTrue else {
+                sideEffects()
+                return // comment
+            }
+            guard otherCondition else {
+                ↓return assertionfailure("")
+            }
+            differentSideEffect()
+        }
+        """),
+        Example("""
+        func test() {
+            guard otherCondition else {
+                ↓return assertionfailure(""); // comment
+            }
+            differentSideEffect()
+        }
+        """),
+        Example("""
+        func test() {
+          if x {
+            ↓return foo()
+          }
+          bar()
+        }
+        """),
+        Example("""
+        func test() {
+          switch x {
+            case .a:
+              ↓return foo() // return to skip baz()
+            case .b:
+              bar()
+          }
+          baz()
+        }
+        """),
+        Example("""
+        func test() {
+          if check {
+            if otherCheck {
+              ↓return foo()
+            }
+          }
+          bar()
+        }
+        """),
+        Example("""
+        func test() {
+            ↓return foo()
+        }
+        """),
+        Example("""
+        func test() {
+          ↓return foo({
+            return bar()
+          })
+        }
+        """),
+        Example("""
+        func test() {
+          guard x else {
+            ↓return foo()
+          }
+          bar()
+        }
+        """),
+        Example("""
+        func test() {
+          let closure: () -> () = {
+            return assert()
+          }
+          if check {
+            if otherCheck {
+              return // comments are fine
+            }
+          }
+          ↓return foo()
+        }
+        """)
+    ]
+}

SwiftLint.xcodeproj/project.pbxproj

@@ -295,6 +295,8 @@
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+		D4492B9323DD499A004EC27B /* _CSwiftSyntax.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = D4492B9123DD499A004EC27B /* _CSwiftSyntax.framework */; settings = {ATTRIBUTES = (Weak, ); }; };
+		D4492B9523DD499A004EC27B /* SwiftSyntax.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = D4492B9223DD499A004EC27B /* SwiftSyntax.framework */; settings = {ATTRIBUTES = (Weak, ); }; };
 		D44AD2761C0AA5350048F7B0 /* LegacyConstructorRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D44AD2741C0AA3730048F7B0 /* LegacyConstructorRule.swift */; };
 		D450D1D121EC4A6900E60010 /* StrongIBOutletRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D450D1D021EC4A6900E60010 /* StrongIBOutletRule.swift */; };
 		D450D1DD21F199F700E60010 /* TrailingClosureConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = D450D1DA21F1992E00E60010 /* TrailingClosureConfiguration.swift */; };
@@ -366,11 +368,14 @@
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+		D4E4FB5523E7A6CF00746FCD /* ReturnValueFromVoidFunctionRuleExamples.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4E4FB5323E7A6CF00746FCD /* ReturnValueFromVoidFunctionRuleExamples.swift */; };
+		D4E4FB5623E7A6CF00746FCD /* ReturnValueFromVoidFunctionRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4E4FB5423E7A6CF00746FCD /* ReturnValueFromVoidFunctionRule.swift */; };
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 		D4EA77C81F817FD200C315FB /* UnneededBreakInSwitchRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4EA77C71F817FD200C315FB /* UnneededBreakInSwitchRule.swift */; };
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 		D4EAB3A420E9948E0051C09A /* AutomaticRuleTests.generated.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4EAB3A320E9948D0051C09A /* AutomaticRuleTests.generated.swift */; };
 		D4EABD0C22CE6F5B00635667 /* VerticalParameterAlignmentRuleExamples.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4EABD0B22CE6F5B00635667 /* VerticalParameterAlignmentRuleExamples.swift */; };
+		D4EF8EA223E695EA0038C26E /* SyntaxRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4EF8EA123E695EA0038C26E /* SyntaxRule.swift */; };
 		D4F10614229A2F5E00FDE319 /* NoFallthroughOnlyRuleExamples.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4F10613229A2F5E00FDE319 /* NoFallthroughOnlyRuleExamples.swift */; };
 		D4F10616229A331200FDE319 /* LegacyMultipleRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4F10615229A331200FDE319 /* LegacyMultipleRule.swift */; };
 		D4F5851520E99A8A0085C6D8 /* TrailingWhitespaceTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4F5851320E99A720085C6D8 /* TrailingWhitespaceTests.swift */; };
@@ -820,6 +825,8 @@
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 		D4470D5C1EB8004B008A1B2E /* VerticalParameterAlignmentOnCallRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = VerticalParameterAlignmentOnCallRule.swift; sourceTree = "<group>"; };
+		D4492B9123DD499A004EC27B /* _CSwiftSyntax.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; path = _CSwiftSyntax.framework; sourceTree = BUILT_PRODUCTS_DIR; };
+		D4492B9223DD499A004EC27B /* SwiftSyntax.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; path = SwiftSyntax.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		D44AD2741C0AA3730048F7B0 /* LegacyConstructorRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = LegacyConstructorRule.swift; sourceTree = "<group>"; };
 		D450D1D021EC4A6900E60010 /* StrongIBOutletRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StrongIBOutletRule.swift; sourceTree = "<group>"; };
 		D450D1DA21F1992E00E60010 /* TrailingClosureConfiguration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TrailingClosureConfiguration.swift; sourceTree = "<group>"; };
@@ -892,11 +899,14 @@
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+		D4E4FB5323E7A6CF00746FCD /* ReturnValueFromVoidFunctionRuleExamples.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ReturnValueFromVoidFunctionRuleExamples.swift; sourceTree = "<group>"; };
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 		D4EA77C71F817FD200C315FB /* UnneededBreakInSwitchRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UnneededBreakInSwitchRule.swift; sourceTree = "<group>"; };
 		D4EA77C91F81FACC00C315FB /* LiteralExpressionEndIdentationRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LiteralExpressionEndIdentationRule.swift; sourceTree = "<group>"; };
 		D4EAB3A320E9948D0051C09A /* AutomaticRuleTests.generated.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AutomaticRuleTests.generated.swift; sourceTree = "<group>"; };
 		D4EABD0B22CE6F5B00635667 /* VerticalParameterAlignmentRuleExamples.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VerticalParameterAlignmentRuleExamples.swift; sourceTree = "<group>"; };
+		D4EF8EA123E695EA0038C26E /* SyntaxRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SyntaxRule.swift; sourceTree = "<group>"; };
 		D4F10613229A2F5E00FDE319 /* NoFallthroughOnlyRuleExamples.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NoFallthroughOnlyRuleExamples.swift; sourceTree = "<group>"; };
 		D4F10615229A331200FDE319 /* LegacyMultipleRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LegacyMultipleRule.swift; sourceTree = "<group>"; };
 		D4F5851320E99A720085C6D8 /* TrailingWhitespaceTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TrailingWhitespaceTests.swift; sourceTree = "<group>"; };
@@ -998,8 +1008,10 @@
 			buildActionMask = 2147483647;
 			files = (
 				E876BFBE1B07828500114ED5 /* SourceKittenFramework.framework in Frameworks */,
+				D4492B9323DD499A004EC27B /* _CSwiftSyntax.framework in Frameworks */,
 				E8C0DFCD1AD349DB007EE3D4 /* SWXMLHash.framework in Frameworks */,
 				3BBF2F9D1C640A0F006CD775 /* SwiftyTextTable.framework in Frameworks */,
+				D4492B9523DD499A004EC27B /* SwiftSyntax.framework in Frameworks */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -1356,6 +1368,8 @@
 				D41E7E0A1DF9DABB0065259A /* RedundantStringEnumValueRule.swift */,
 				6208ED4E20C297AC004E78D1 /* RedundantTypeAnnotationRule.swift */,
 				D4B022B11E10B613007E5297 /* RedundantVoidReturnRule.swift */,
+				D4E4FB5423E7A6CF00746FCD /* ReturnValueFromVoidFunctionRule.swift */,
+				D4E4FB5323E7A6CF00746FCD /* ReturnValueFromVoidFunctionRuleExamples.swift */,
 				D4D383842145F550000235BD /* StaticOperatorRule.swift */,
 				D42B45D81F0AF5E30086B683 /* StrictFilePrivateRule.swift */,
 				D44254251DB9C12300492EA4 /* SyntacticSugarRule.swift */,
@@ -1391,6 +1405,7 @@
 				D0D1211A19E87861005E4BAA /* swiftlint */,
 				D0D1216E19E87B05005E4BAA /* SwiftLintFramework */,
 				D0D1217B19E87B05005E4BAA /* SwiftLintFrameworkTests */,
+				D4492B9023DD499A004EC27B /* Frameworks */,
 			);
 			indentWidth = 4;
 			sourceTree = "<group>";
@@ -1615,6 +1630,15 @@
 			path = "Supporting Files";
 			sourceTree = "<group>";
 		};
+		D4492B9023DD499A004EC27B /* Frameworks */ = {
+			isa = PBXGroup;
+			children = (
+				D4492B9123DD499A004EC27B /* _CSwiftSyntax.framework */,
+				D4492B9223DD499A004EC27B /* SwiftSyntax.framework */,
+			);
+			name = Frameworks;
+			sourceTree = "<group>";
+		};
 		E802ECFE1C56A54600A35AE1 /* Helpers */ = {
 			isa = PBXGroup;
 			children = (
@@ -1674,6 +1698,7 @@
 			isa = PBXGroup;
 			children = (
 				E88DEA8B1B0999A000A66CB0 /* ASTRule.swift */,
+				D4EF8EA123E695EA0038C26E /* SyntaxRule.swift */,
 				E80746F51ECB722F00548D31 /* CacheDescriptionProvider.swift */,
 				A73469401FB12149009B57C7 /* CallPairRule.swift */,
 				E86396C11BADAAE5002C9E88 /* Reporter.swift */,
@@ -2062,6 +2087,7 @@
 				62A3E95D209E084000547A86 /* EmptyXCTestMethodRule.swift in Sources */,
 				D4C4A34C1DEA4FF000E0E04C /* AttributesConfiguration.swift in Sources */,
 				29FC197A21382C07006D208C /* DuplicateImportsRuleExamples.swift in Sources */,
+				D4E4FB5623E7A6CF00746FCD /* ReturnValueFromVoidFunctionRule.swift in Sources */,
 				83D71E281B131ECE000395DE /* RuleDescription.swift in Sources */,
 				D4470D571EB69225008A1B2E /* ImplicitReturnRule.swift in Sources */,
 				8FE3CCBC22DBF8D000B8EA87 /* UnusedDeclarationConfiguration.swift in Sources */,
@@ -2077,6 +2103,7 @@
 				D4C4A3521DEFBBB700E0E04C /* FileHeaderConfiguration.swift in Sources */,
 				623675B01F960C5C009BE6F3 /* QuickDiscouragedPendingTestRule.swift in Sources */,
 				287F8B642230843000BDC504 /* NSLocalizedStringRequireBundleRule.swift in Sources */,
+				D4EF8EA223E695EA0038C26E /* SyntaxRule.swift in Sources */,
 				D47079AD1DFE2FA700027086 /* EmptyParametersRule.swift in Sources */,
 				E87E4A091BFB9CAE00FCFE46 /* SyntaxKind+SwiftLint.swift in Sources */,
 				3B0B14541C505D6300BE82F7 /* SeverityConfiguration.swift in Sources */,
@@ -2322,6 +2349,7 @@
 				C946FECB1EAE67EE007DD778 /* LetVarWhitespaceRule.swift in Sources */,
 				E881985D1BEA97EB00333A11 /* TrailingWhitespaceRule.swift in Sources */,
 				E832F10B1B17E2F5003F265F /* FileManager+SwiftLint.swift in Sources */,
+				D4E4FB5523E7A6CF00746FCD /* ReturnValueFromVoidFunctionRuleExamples.swift in Sources */,
 				E816194C1BFBF35D00946723 /* SwiftDeclarationKind+SwiftLint.swift in Sources */,
 				D4DABFD71E2C23B1009617B6 /* NotificationCenterDetachmentRule.swift in Sources */,
 				3BA79C9B1C4767910057E705 /* NSRange+SwiftLint.swift in Sources */,
@@ -2480,7 +2508,7 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = D0D1212619E878CC005E4BAA /* Debug.xcconfig */;
 			buildSettings = {
-				MACOSX_DEPLOYMENT_TARGET = 10.10;
+				MACOSX_DEPLOYMENT_TARGET = 10.12;
 				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
@@ -2489,7 +2517,7 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = D0D1212819E878CC005E4BAA /* Release.xcconfig */;
 			buildSettings = {
-				MACOSX_DEPLOYMENT_TARGET = 10.10;
+				MACOSX_DEPLOYMENT_TARGET = 10.12;
 				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
@@ -2566,7 +2594,7 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = D0D1212719E878CC005E4BAA /* Profile.xcconfig */;
 			buildSettings = {
-				MACOSX_DEPLOYMENT_TARGET = 10.10;
+				MACOSX_DEPLOYMENT_TARGET = 10.12;
 				SWIFT_VERSION = 4.0;
 			};
 			name = Profile;
@@ -2609,7 +2637,7 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = D0D1212919E878CC005E4BAA /* Test.xcconfig */;
 			buildSettings = {
-				MACOSX_DEPLOYMENT_TARGET = 10.10;
+				MACOSX_DEPLOYMENT_TARGET = 10.12;
 				SWIFT_VERSION = 4.0;
 			};
 			name = Test;

SwiftLint.xcworkspace/contents.xcworkspacedata

@@ -16,6 +16,9 @@
    <FileRef
       location = "group:Carthage/Checkouts/SwiftyTextTable/SwiftyTextTable.xcodeproj">
    </FileRef>
+   <FileRef
+      location = "group:SwiftSyntax/SwiftSyntax.xcodeproj">
+   </FileRef>
    <FileRef
       location = "group:Carthage/Checkouts/Yams/Yams.xcodeproj">
    </FileRef>

SwiftSyntax

@@ -0,0 +1 @@
+Subproject commit 3e3eb191fcdbecc6031522660c4ed6ce25282c25

Tests/LinuxMain.swift

@@ -1260,6 +1260,12 @@ extension ReturnArrowWhitespaceRuleTests {
     ]
 }
 
+extension ReturnValueFromVoidFunctionRuleTests {
+    static var allTests: [(String, (ReturnValueFromVoidFunctionRuleTests) -> () throws -> Void)] = [
+        ("testWithDefaultConfiguration", testWithDefaultConfiguration)
+    ]
+}
+
 extension RuleConfigurationTests {
     static var allTests: [(String, (RuleConfigurationTests) -> () throws -> Void)] = [
         ("testNameConfigurationSetsCorrectly", testNameConfigurationSetsCorrectly),
@@ -1816,6 +1822,7 @@ XCTMain([
     testCase(RequiredDeinitRuleTests.allTests),
     testCase(RequiredEnumCaseRuleTestCase.allTests),
     testCase(ReturnArrowWhitespaceRuleTests.allTests),
+    testCase(ReturnValueFromVoidFunctionRuleTests.allTests),
     testCase(RuleConfigurationTests.allTests),
     testCase(RuleTests.allTests),
     testCase(RulesTests.allTests),

Tests/SwiftLintFrameworkTests/AutomaticRuleTests.generated.swift

@@ -648,6 +648,12 @@ class ReturnArrowWhitespaceRuleTests: XCTestCase {
     }
 }
 
+class ReturnValueFromVoidFunctionRuleTests: XCTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(ReturnValueFromVoidFunctionRule.description)
+    }
+}
+
 class ShorthandOperatorRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(ShorthandOperatorRule.description)

Tests/SwiftLintFrameworkTests/ConfigurationTests+Nested.swift

@@ -88,7 +88,8 @@ extension ConfigurationTests {
         let mergedConfiguration = projectMockConfig0CustomRules.merge(with: projectMockConfig2CustomRules)
         guard let mergedCustomRules = mergedConfiguration.rules.first(where: { $0 is CustomRules }) as? CustomRules
             else {
-            return XCTFail("Custom rule are expected to be present")
+            XCTFail("Custom rule are expected to be present")
+            return
         }
         XCTAssertTrue(
             mergedCustomRules.configuration.customRuleConfigurations.contains(where: { $0.identifier == "no_abc" })
@@ -102,7 +103,8 @@ extension ConfigurationTests {
         let mergedConfiguration = projectMockConfig0CustomRules.merge(with: projectMockConfig2CustomRulesDisabled)
         guard let mergedCustomRules = mergedConfiguration.rules.first(where: { $0 is CustomRules }) as? CustomRules
             else {
-            return XCTFail("Custom rule are expected to be present")
+            XCTFail("Custom rule are expected to be present")
+            return
         }
         XCTAssertFalse(
             mergedCustomRules.configuration.customRuleConfigurations.contains(where: { $0.identifier == "no_abc" })

azure-pipelines.yml

@@ -23,15 +23,11 @@ jobs:
   strategy:
     maxParallel: 10
     matrix:
-      xcode102:
-        DEVELOPER_DIR: /Applications/Xcode_10.2.app
-      xcode103:
-        DEVELOPER_DIR: /Applications/Xcode_10.3.app
       xcode111:
         DEVELOPER_DIR: /Applications/Xcode_11.1.app
   steps:
-    - script: git submodule update --init --recursive
+    - script: Script/bootstrap
-      displayName: Update git submodules
+      displayName: Bootstrap
     - script: |
         sw_vers
         xcodebuild -version

script/bootstrap

@@ -21,6 +21,8 @@ main ()
         echo "*** Updating submodules..."
         update_submodules
     fi
+
+    cd "SwiftSyntax" && swift package generate-xcodeproj
 }
 
 bootstrap_submodule ()