Add back `tuple_pattern` rule

Fixes #3466

CHANGELOG.md

@@ -30,6 +30,12 @@
   `return <expression>` in a function that returns `Void`.  
   [Marcelo Fabri](https://github.com/marcelofabri)
 
+* Add back `tuple_pattern` rule to warn against assigning variables
+  through a tuple pattern when the left side of the assignment
+  contains labels.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+  [#3466](https://github.com/realm/SwiftLint/issues/3466)
+
 * Don't skip autocorrect on files that have parser warnings. Only files with
   errors reported by the Swift parser will be skipped.  
   [Marcelo Fabri](https://github.com/marcelofabri)

Source/SwiftLintFramework/Models/PrimaryRuleList.swift

@@ -183,6 +183,7 @@ public let primaryRuleList = RuleList(rules: [
     TrailingNewlineRule.self,
     TrailingSemicolonRule.self,
     TrailingWhitespaceRule.self,
+    TuplePatternRule.self,
     TypeBodyLengthRule.self,
     TypeContentsOrderRule.self,
     TypeNameRule.self,

Source/SwiftLintFramework/Rules/Idiomatic/TuplePatternRule.swift

@@ -0,0 +1,88 @@
+import SourceKittenFramework
+import SwiftSyntax
+
+public struct TuplePatternRule: ConfigurationProviderRule, 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] {
+        guard let syntaxTree = file.syntaxTree else {
+            return []
+        }
+
+        let visitor = TuplePatternVisitor()
+        visitor.walk(syntaxTree)
+        return visitor.violations(for: self, in: file)
+    }
+}
+
+private class TuplePatternVisitor: SyntaxVisitor {
+    private var positions = [AbsolutePosition]()
+
+    override func visitPost(_ node: PatternBindingSyntax) {
+        guard let tuplePattern = node.pattern.as(TuplePatternSyntax.self),
+            case let leftSideLabels = tuplePattern.labels,
+            !leftSideLabels.compactMap({ $0 }).isEmpty,
+            let rightSideLabels = node.initializer?.tupleElementList?.labels,
+            leftSideLabels != rightSideLabels else {
+            return
+        }
+
+        positions.append(node.positionAfterSkippingLeadingTrivia)
+    }
+
+    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: TupleExprElementListSyntax? {
+        if let expr = value.as(TupleExprSyntax.self) {
+            return expr.elementList
+        }
+
+        return nil
+    }
+}
+
+private extension TupleExprElementListSyntax {
+    var labels: [String?] {
+        return map { element in
+            element.label?.withoutTrivia().text
+        }
+    }
+}

Tests/SwiftLintFrameworkTests/AutomaticRuleTests.generated.swift

@@ -785,6 +785,12 @@ class TrailingSemicolonRuleTests: XCTestCase {
     }
 }
 
+class TuplePatternRuleTests: XCTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(TuplePatternRule.description)
+    }
+}
+
 class TypeBodyLengthRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(TypeBodyLengthRule.description)