Implement no labels in case patterns. (swiftlang#90)

Author: LaurenWhite

Sources/Rules/NoLabelsInCasePatterns.swift

@@ -12,6 +12,56 @@ import SwiftSyntax
 /// Format: Redundant labels in case patterns are removed.
 ///
 /// - SeeAlso: https://google.github.io/swift#pattern-matching
-public final class NoLablesInCasePatterns: SyntaxFormatRule {
+public final class NoLabelsInCasePatterns: SyntaxFormatRule {
+  public override func visit(_ node: SwitchCaseLabelSyntax) -> Syntax {
 
+    var newCaseItems: [CaseItemSyntax] = []
+    for item in node.caseItems {
+      guard let expPat = item.pattern as? ExpressionPatternSyntax else {
+        newCaseItems.append(item)
+        continue
+      }
+      guard let funcCall = expPat.expression as? FunctionCallExprSyntax else {
+        newCaseItems.append(item)
+        continue
+      }
+
+      // Search function call argument list for violations
+      var newArgs: [FunctionCallArgumentSyntax] = []
+      for argument in funcCall.argumentList {
+        guard let label = argument.label else {
+          newArgs.append(argument)
+          continue
+        }
+        guard let unresolvedPat = argument.expression as? UnresolvedPatternExprSyntax,
+          let valueBinding = unresolvedPat.pattern as? ValueBindingPatternSyntax else {
+          newArgs.append(argument)
+          continue
+        }
+
+        // Remove label if it's the same as the value identifier
+        let name = valueBinding.valuePattern.description.trimmingCharacters(in: .whitespaces)
+        guard name == label.text else {
+          newArgs.append(argument)
+          continue
+        }
+        diagnose(.removeRedundantLabel(name: name), on: label)
+        newArgs.append(argument.withLabel(nil).withColon(nil))
+      }
+      
+      let newArgList = SyntaxFactory.makeFunctionCallArgumentList(newArgs)
+      let newFuncCall = funcCall.withArgumentList(newArgList)
+      let newExpPat = expPat.withExpression(newFuncCall)
+      let newItem = item.withPattern(newExpPat)
+      newCaseItems.append(newItem)
+    }
+    let newCaseItemList = SyntaxFactory.makeCaseItemList(newCaseItems)
+    return node.withCaseItems(newCaseItemList)
+  }
+}
+
+extension Diagnostic.Message {
+  static func removeRedundantLabel(name: String) -> Diagnostic.Message {
+    return .init(.warning, "remove \(name) label from case argument")
+  }
 }

Tests/SwiftFormatTests/NoLabelsInCasePatternsTests.swift

@@ -0,0 +1,43 @@
+import Foundation
+import XCTest
+import SwiftSyntax
+
+@testable import Rules
+
+public class NoLabelsInCasePatternsTests: DiagnosingTestCase {
+  public func testRedundantCaseLabels() {
+    XCTAssertFormatting(
+      NoLabelsInCasePatterns.self,
+      input: """
+             switch treeNode {
+             case .root(let data):
+               break
+             case .subtree(left: let left, right: let right):
+               break
+             case .leaf(element: let element):
+               break
+             }
+             """,
+      expected: """
+                switch treeNode {
+                case .root(let data):
+                  break
+                case .subtree(let left, let right):
+                  break
+                case .leaf(let element):
+                  break
+                }
+                """)
+    XCTAssertNotDiagnosed(.removeRedundantLabel(name: "data"))
+    XCTAssertDiagnosed(.removeRedundantLabel(name: "left"))
+    XCTAssertDiagnosed(.removeRedundantLabel(name: "right"))
+    XCTAssertDiagnosed(.removeRedundantLabel(name: "element"))
+  }
+
+  #if !os(macOS)
+  static let allTests = [
+    NoLabelsInCasePatternsTests.testRedundantCaseLabels,
+    ]
+  #endif
+}
+