Implement NoEmptyAssociatedValues rule and tests. (swiftlang#61)

Author: LaurenWhite

tools/swift-format/Sources/Rules/NoEmptyAssociatedValues.swift

@@ -11,5 +11,21 @@ import SwiftSyntax
 ///
 /// - SeeAlso: https://google.github.io/swift#enum-cases
 public final class NoEmptyAssociatedValues: SyntaxFormatRule {
+  public override func visit(_ node: EnumCaseDeclSyntax) -> DeclSyntax {
+    for element in node.elements {
+      guard let associatedValue = element.associatedValue else { continue }
+      if associatedValue.parameterList.count == 0 {
+        diagnose(.removeEmptyParentheses(name: element.identifier.text), on: element)
+        let newDecl = node.withElements(node.elements.replacing(childAt: element.indexInParent, with: element.withAssociatedValue(nil)))
+        return newDecl
+      }
+    }
+    return node
+  }
+}
 
+extension Diagnostic.Message {
+  static func removeEmptyParentheses(name: String) -> Diagnostic.Message {
+    return .init(.warning, "Remove '()' after \(name)")
+  }
 }

tools/swift-format/Tests/SwiftFormatTests/NoEmptyAssociatedValuesTests.swift

@@ -0,0 +1,35 @@
+import Foundation
+import XCTest
+import SwiftSyntax
+
+@testable import Rules
+
+public class NoEmptyAssociatedValuesTests: DiagnosingTestCase {
+    func testEmptyAssociatedValue() {
+        XCTAssertFormatting(NoEmptyAssociatedValues.self,
+                            input: """
+                               enum CompassPoint {
+                                 case north
+                                 private case east()
+                                 case south(String)
+                                 indirect case west
+                                 case northeast()
+                               }
+                               """,
+                            expected: """
+                                  enum CompassPoint {
+                                    case north
+                                    private case east
+                                    case south(String)
+                                    indirect case west
+                                    case northeast
+                                  }
+                                  """)
+    }
+    
+    #if !os(macOS)
+    static let allTests = [
+        NoEmptyAssociatedValuesTests.testEmptyAssociatedValue,
+        ]
+    #endif
+}