Implement NoEmptyTrailingClosureParentheses (swiftlang#83)

Author: LaurenWhite

Sources/Rules/NoEmptyTrailingClosureParentheses.swift

@@ -10,6 +10,24 @@ import SwiftSyntax
 /// Format: Empty parentheses in function calls with trailing closures will be removed.
 ///
 /// - SeeAlso: https://google.github.io/swift#trailing-closures
-public final class NoEmptyTrailingClosureParentheses: SyntaxLintRule {
+public final class NoEmptyTrailingClosureParentheses: SyntaxFormatRule {
 
+  public override func visit(_ node: FunctionCallExprSyntax) -> ExprSyntax {
+    guard node.argumentList.count == 0 else { return node }
+
+    guard let name = node.calledExpression.firstToken?.withoutTrivia() else { return node }
+    diagnose(.removeEmptyTrailingParentheses(name: "\(name)"), on: node)
+
+    let formattedExp = replaceTrivia(on: node.calledExpression,
+                                     token: node.calledExpression.lastToken,
+                                     trailingTrivia: .spaces(1)) as! ExprSyntax
+    return node.withLeftParen(nil).withRightParen(nil).withCalledExpression(formattedExp)
+  }
+}
+
+
+extension Diagnostic.Message {
+  static func removeEmptyTrailingParentheses(name: String) -> Diagnostic.Message {
+    return .init(.warning, "remove '()' after \(name)")
+  }
 }

Tests/SwiftFormatTests/NoEmptyTrailingClosureParenthesesTests.swift

@@ -0,0 +1,40 @@
+import Foundation
+import XCTest
+import SwiftSyntax
+
+@testable import Rules
+
+public class NoEmptyTrailingClosureParenthesesTests: DiagnosingTestCase {
+  public func testInvalidEmptyParenTrailingClosure() {
+    XCTAssertFormatting(
+      NoEmptyTrailingClosureParentheses.self,
+      input: """
+             func greetEnthusiastically(_ nameProvider: () -> String) {
+               // ...
+             }
+             func greetApathetically(_ nameProvider: () -> String) {
+               // ...
+             }
+             greetEnthusiastically() { "John" }
+             greetApathetically { "not John" }
+             """,
+      expected: """
+                func greetEnthusiastically(_ nameProvider: () -> String) {
+                  // ...
+                }
+                func greetApathetically(_ nameProvider: () -> String) {
+                  // ...
+                }
+                greetEnthusiastically { "John" }
+                greetApathetically { "not John" }
+                """)
+    XCTAssertDiagnosed(.removeEmptyTrailingParentheses(name: "greetEnthusiastically"))
+  }
+
+  #if !os(macOS)
+  static let allTests = [
+    NoEmptyTrailingClosureParenthesesTests.testInvalidEmptyParenTrailingClosure,
+    ]
+  #endif
+
+}