Merge pull request swiftlang#211 from dylansturg/no_trailing_spaces

Remove trailing spaces from comments and keep spaces after block comments.

Author: allevato

Sources/SwiftFormatPrettyPrint/Comment.swift

@@ -14,6 +14,24 @@ import Foundation
 import SwiftFormatConfiguration
 import SwiftSyntax
 
+extension StringProtocol {
+  /// Trims whitespace from the end of a string, returning a new string with no trailing whitespace.
+  ///
+  /// If the string is only whitespace, an empty string is returned.
+  ///
+  /// - Returns: The string with trailing whitespace removed.
+  func trimmingTrailingWhitespace() -> String {
+    if isEmpty { return String() }
+    let scalars = unicodeScalars
+    var idx = scalars.index(before: scalars.endIndex)
+    while scalars[idx].properties.isWhitespace {
+      if idx == scalars.startIndex { return String() }
+      idx = scalars.index(before: idx)
+    }
+    return String(String.UnicodeScalarView(scalars[...idx]))
+  }
+}
+
 struct Comment {
   enum Kind {
     case line, docLine, block, docBlock
@@ -47,17 +65,23 @@ struct Comment {
 
     switch kind {
     case .line, .docLine:
-      self.text = [text]
+      self.text = [text.trimmingTrailingWhitespace()]
       self.text[0].removeFirst(kind.prefixLength)
       self.length = self.text.reduce(0, { $0 + $1.count + kind.prefixLength + 1 })
 
     case .block, .docBlock:
       var fulltext: String = text
       fulltext.removeFirst(kind.prefixLength)
       fulltext.removeLast(2)
-      self.text = fulltext.split(separator: "\n", omittingEmptySubsequences: false).map {
-        String($0)
+      let lines = fulltext.split(separator: "\n", omittingEmptySubsequences: false)
+
+      // The last line in a block style comment contains the "*/" pattern to end the comment. The
+      // trailing space(s) need to be kept in that line to have space between text and "*/".
+      var trimmedLines = lines.dropLast().map({ $0.trimmingTrailingWhitespace() })
+      if let lastLine = lines.last {
+        trimmedLines.append(String(lastLine))
       }
+      self.text = trimmedLines
       self.length = self.text.reduce(0, { $0 + $1.count }) + kind.prefixLength + 3
     }
   }

Sources/SwiftFormatPrettyPrint/TokenStreamCreator.swift

@@ -2730,10 +2730,15 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
       case .blockComment(let text):
         if index > 0 || isStartOfFile {
           appendToken(.comment(Comment(kind: .block, text: text), wasEndOfLine: false))
-          // We place a size-0 break after the comment to allow a discretionary newline after the
-          // comment if the user places one here but the comment is otherwise adjacent to a text
-          // token.
-          appendToken(.break(.same, size: 0))
+          // There is always a break after the comment to allow a discretionary newline after it.
+          var breakSize = 0
+          if index + 1 < trivia.endIndex {
+            let nextPiece = trivia[index + 1]
+            // The original number of spaces is intentionally discarded, but 1 space is allowed in
+            // case the comment is followed by another token instead of a newline.
+            if case .spaces = nextPiece { breakSize = 1 }
+          }
+          appendToken(.break(.same, size: breakSize))
           isStartOfFile = false
         }
         requiresNextNewline = false

Tests/SwiftFormatPrettyPrintTests/CommentTests.swift

@@ -639,5 +639,47 @@ final class CommentTests: PrettyPrintTestCase {
     assertPrettyPrintEqual(input: input, expected: expected, linelength: 100)
   }
 
+  func testTrailingSpacesInComments() {
+    // Xcode has a commonly enabled setting to delete trailing spaces, which also applies to
+    // multi-line strings. The trailing spaces are intentionally written using a unicode escape
+    // sequence to ensure they aren't deleted.
+    let input = """
+      /// This is a trailing space documentation comment.\u{0020}\u{0020}\u{0020}\u{0020}\u{0020}
+      ///        This is a leading space documentation comment.
+      func foo() {
+        //       leading spaces are fine
+        // trailing spaces should go\u{0020}\u{0020}\u{0020}\u{0020}\u{0020}
+        let out = "123"
+      }
 
+      /**
+       *    This is a leading space doc block comment
+       * This is a trailing space doc block comment\u{0020}\u{0020}\u{0020}\u{0020}\u{0020}
+       */
+      func foo() {
+        /*    block comment    */ let out = "123"
+      }
+      """
+
+    let expected = """
+      /// This is a trailing space documentation comment.
+      ///        This is a leading space documentation comment.
+      func foo() {
+        //       leading spaces are fine
+        // trailing spaces should go
+        let out = "123"
+      }
+
+      /**
+       *    This is a leading space doc block comment
+       * This is a trailing space doc block comment
+       */
+      func foo() {
+        /*    block comment    */ let out = "123"
+      }
+
+      """
+
+    assertPrettyPrintEqual(input: input, expected: expected, linelength: 60)
+  }
 }