Merge pull request swiftlang#198 from google/format-fix-extension-leading-trivia

Keep leading trivia when removing extension modifier.

Author: dabelknap

Sources/SwiftFormatRules/NoAccessLevelOnExtensionDeclaration.swift

@@ -40,8 +40,12 @@ public final class NoAccessLevelOnExtensionDeclaration: SyntaxFormatRule {
         leftBrace: node.members.leftBrace,
         members: addMemberAccessKeywords(memDeclBlock: node.members, keyword: accessKeyword),
         rightBrace: node.members.rightBrace)
+      let newKeyword = replaceTrivia(on: node.extensionKeyword,
+                                     token: node.extensionKeyword,
+                                     leadingTrivia: accessKeyword.leadingTrivia) as! TokenSyntax
       return node.withMembers(newMembers)
-              .withModifiers(modifiers.remove(name: accessKeyword.name.text))
+        .withModifiers(modifiers.remove(name: accessKeyword.name.text))
+        .withExtensionKeyword(newKeyword)
     // Internal keyword redundant, delete
     case .internalKeyword:
       diagnose(.removeRedundantAccessKeyword(name: node.extendedType.description),

Tests/SwiftFormatRulesTests/NoAccessLevelOnExtensionDeclarationTests.swift

@@ -49,6 +49,42 @@ public class NoAccessLevelOnExtensionDeclarationTests: DiagnosingTestCase {
     )
   }
 
+  public func testPreservesCommentOnRemovedModifier() {
+    XCTAssertFormatting(
+      NoAccessLevelOnExtensionDeclaration.self,
+      input: """
+        /// This doc comment should stick around.
+        public extension Foo {
+          func f() {}
+          // This should not change.
+          func g() {}
+        }
+
+        /// So should this one.
+        internal extension Foo {
+          func f() {}
+          // This should not change.
+          func g() {}
+        }
+        """,
+      expected: """
+        /// This doc comment should stick around.
+        extension Foo {
+          public func f() {}
+          // This should not change.
+          public func g() {}
+        }
+
+        /// So should this one.
+        extension Foo {
+          func f() {}
+          // This should not change.
+          func g() {}
+        }
+        """
+    )
+  }
+
 #if !os(macOS)
 static let allTests = [
   NoAccessLevelOnExtensionDeclarationTests.testExtensionDeclarationAccessLevel,