Add tuple_pattern opt-in rule

CHANGELOG.md

@@ -34,6 +34,12 @@
   [SwiftSyntax](https://github.com/apple/swift-syntax).  
   [Marcelo Fabri](https://github.com/marcelofabri)
 
+* Add `tuple_pattern` opt-in rule to warn against using
+  assigning variables through a tuple pattern when the left side
+  of the assignment contains labels.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+  [#2203](https://github.com/realm/SwiftLint/issues/2203)
+
 * 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)

Source/SwiftLintFramework/Models/MasterRuleList.swift

@@ -167,6 +167,7 @@ public let masterRuleList = RuleList(rules: [
     TrailingNewlineRule.self,
     TrailingSemicolonRule.self,
     TrailingWhitespaceRule.self,
+    TuplePatternRule.self,
     TypeBodyLengthRule.self,
     TypeContentsOrderRule.self,
     TypeNameRule.self,

Source/SwiftLintFramework/Rules/Idiomatic/TuplePatternRule.swift

@@ -0,0 +1,89 @@
+import SourceKittenFramework
+#if canImport(SwiftSyntax)
+import SwiftSyntax
+#endif
+
+public struct TuplePatternRule: ConfigurationProviderRule, SyntaxRule, AutomaticTestableRule {
+    public var configuration = SeverityConfiguration(.warning)
+
+    public init() {}
+
+    public static let description = RuleDescription(
+        identifier: "tuple_pattern",
+        name: "Tuple Pattern",
+        description: "Assigning variables through a tuple pattern is only permitted if the left-hand side of the " +
+                     "assignment is unlabeled.",
+        kind: .idiomatic,
+        minSwiftVersion: .fiveDotOne,
+        nonTriggeringExamples: [
+            Example("let (a, b) = (y: 4, x: 5.0)"),
+            Example("let (a, b) = (4, 5.0)"),
+            Example("let (a, b) = (a: 4, b: 5.0)"),
+            Example("let (a, b) = tuple")
+        ],
+        triggeringExamples: [
+            Example("let ↓(x: a, y: b) = (y: 4, x: 5.0)"),
+            Example("let ↓(x: Int, y: Double) = (y: 4, x: 5.0)"),
+            Example("let ↓(x: Int, y: Double) = (y: 4, x: 5.0)")
+        ]
+    )
+
+    public func validate(file: SwiftLintFile) -> [StyleViolation] {
+        #if canImport(SwiftSyntax)
+        return validate(file: file, visitor: PatternBindingVisitor())
+        #else
+        return []
+        #endif
+    }
+}
+
+#if canImport(SwiftSyntax)
+private class PatternBindingVisitor: SyntaxRuleVisitor {
+    private var positions = [AbsolutePosition]()
+
+    func visit(_ node: PatternBindingSyntax) -> SyntaxVisitorContinueKind {
+        if let tuplePattern = node.pattern as? TuplePatternSyntax,
+            case let leftSideLabels = tuplePattern.labels,
+            !leftSideLabels.compactMap({ $0 }).isEmpty,
+            let rightSideLabels = node.initializer?.tupleElementList?.labels,
+            leftSideLabels != rightSideLabels {
+            positions.append(node.positionAfterSkippingLeadingTrivia)
+        }
+        return .visitChildren
+    }
+
+    func violations(for rule: TuplePatternRule, 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 TuplePatternSyntax {
+    var labels: [String?] {
+        return elements.map { element in
+            element.labelName?.withoutTrivia().text
+        }
+    }
+}
+
+private extension InitializerClauseSyntax {
+    var tupleElementList: TupleElementListSyntax? {
+        if let expr = value as? TupleExprSyntax {
+            return expr.elementList
+        }
+
+        return nil
+    }
+}
+
+private extension TupleElementListSyntax {
+    var labels: [String?] {
+        return map { element in
+            element.label?.withoutTrivia().text
+        }
+    }
+}
+#endif

SwiftLint.xcodeproj/project.pbxproj

@@ -307,6 +307,7 @@
 		D46252541DF63FB200BE2CA1 /* NumberSeparatorRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46252531DF63FB200BE2CA1 /* NumberSeparatorRule.swift */; };
 		D466B620233D229F0068190B /* FlatMapOverMapReduceRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D466B61F233D229F0068190B /* FlatMapOverMapReduceRule.swift */; };
 		D467275823DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D467275723DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift */; };
+		D467275A23DE71D200DE73B6 /* TuplePatternRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D467275923DE71D200DE73B6 /* TuplePatternRule.swift */; };
 		D46A317F1F1CEDCD00AF914A /* UnneededParenthesesInClosureArgumentRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46A317E1F1CEDCD00AF914A /* UnneededParenthesesInClosureArgumentRule.swift */; };
 		D46C7C3E23BF2F6A007C517F /* PreferSelfTypeOverTypeOfSelfRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46C7C3D23BF2F6A007C517F /* PreferSelfTypeOverTypeOfSelfRule.swift */; };
 		D46E041D1DE3712C00728374 /* TrailingCommaRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46E041C1DE3712C00728374 /* TrailingCommaRule.swift */; };
@@ -838,6 +839,7 @@
 		D46252531DF63FB200BE2CA1 /* NumberSeparatorRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NumberSeparatorRule.swift; sourceTree = "<group>"; };
 		D466B61F233D229F0068190B /* FlatMapOverMapReduceRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FlatMapOverMapReduceRule.swift; sourceTree = "<group>"; };
 		D467275723DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VoidFunctionInTernaryConditionRule.swift; sourceTree = "<group>"; };
+		D467275923DE71D200DE73B6 /* TuplePatternRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TuplePatternRule.swift; sourceTree = "<group>"; };
 		D46A317E1F1CEDCD00AF914A /* UnneededParenthesesInClosureArgumentRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnneededParenthesesInClosureArgumentRule.swift; sourceTree = "<group>"; };
 		D46C7C3D23BF2F6A007C517F /* PreferSelfTypeOverTypeOfSelfRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PreferSelfTypeOverTypeOfSelfRule.swift; sourceTree = "<group>"; };
 		D46E041C1DE3712C00728374 /* TrailingCommaRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = TrailingCommaRule.swift; sourceTree = "<group>"; };
@@ -1377,6 +1379,7 @@
 				D44254251DB9C12300492EA4 /* SyntacticSugarRule.swift */,
 				7551DF6C21382C9A00AA1F4D /* ToggleBoolRule.swift */,
 				E87E4A041BFB927C00FCFE46 /* TrailingSemicolonRule.swift */,
+				D467275923DE71D200DE73B6 /* TuplePatternRule.swift */,
 				E88DEA911B099B1F00A66CB0 /* TypeNameRule.swift */,
 				D4130D981E16CC1300242361 /* TypeNameRuleExamples.swift */,
 				D4DE9131207B4731000FFAA8 /* UnavailableFunctionRule.swift */,
@@ -2324,6 +2327,7 @@
 				E83530C61ED6328A00FBAF79 /* FileNameRule.swift in Sources */,
 				3BB47D831C514E8100AE6A10 /* RegexConfiguration.swift in Sources */,
 				D401D9261ED85EF0005DA5D4 /* RuleKind.swift in Sources */,
+				D467275A23DE71D200DE73B6 /* TuplePatternRule.swift in Sources */,
 				622AD800216ACE6300A002C6 /* XCTSpecificMatcherRuleExamples.swift in Sources */,
 				82EB7886215BAE790042E0FD /* TypeContentsOrderRuleExamples.swift in Sources */,
 				7551DF6D21382C9A00AA1F4D /* ToggleBoolRule.swift in Sources */,

Tests/LinuxMain.swift

@@ -1449,6 +1449,12 @@ extension TrailingWhitespaceTests {
     ]
 }
 
+extension TuplePatternRuleTests {
+    static var allTests: [(String, (TuplePatternRuleTests) -> () throws -> Void)] = [
+        ("testWithDefaultConfiguration", testWithDefaultConfiguration)
+    ]
+}
+
 extension TypeBodyLengthRuleTests {
     static var allTests: [(String, (TypeBodyLengthRuleTests) -> () throws -> Void)] = [
         ("testWithDefaultConfiguration", testWithDefaultConfiguration)
@@ -1851,6 +1857,7 @@ XCTMain([
     testCase(TrailingCommaRuleTests.allTests),
     testCase(TrailingSemicolonRuleTests.allTests),
     testCase(TrailingWhitespaceTests.allTests),
+    testCase(TuplePatternRuleTests.allTests),
     testCase(TypeBodyLengthRuleTests.allTests),
     testCase(TypeContentsOrderRuleTests.allTests),
     testCase(TypeNameRuleTests.allTests),

Tests/SwiftLintFrameworkTests/AutomaticRuleTests.generated.swift

@@ -720,6 +720,12 @@ class TrailingSemicolonRuleTests: XCTestCase {
     }
 }
 
+class TuplePatternRuleTests: XCTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(TuplePatternRule.description)
+    }
+}
+
 class TypeBodyLengthRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(TypeBodyLengthRule.description)