[clang-format] Align preprocessor comments with #

Summary:
r312125, which introduced preprocessor indentation, shipped with a known
issue where "indentation of comments immediately before indented
preprocessor lines is toggled on each run". For example these two forms
toggle:

  #ifndef HEADER_H
  #define HEADER_H
  #if 1
  // comment
  #   define A 0
  #endif
  #endif

  #ifndef HEADER_H
  #define HEADER_H
  #if 1
     // comment
  #   define A 0
  #endif
  #endif

This happens because we check vertical alignment against the '#' yet
indent to the level of the 'define'. This patch resolves this issue by
aligning against the '#'.

Reviewers: krasimir, klimek, djasper

Reviewed By: krasimir

Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D42408

llvm-svn: 323904

1 files changed, 12 insertions, 9 deletions

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index 9287cbc3a9b..05629eda09b 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -1725,15 +1725,18 @@ void TokenAnnotator::setCommentLineLevels(
       }
     }
 
-    if (NextNonCommentLine && CommentLine) {
-      // If the comment is currently aligned with the line immediately following
-      // it, that's probably intentional and we should keep it.
-      bool AlignedWithNextLine =
-          NextNonCommentLine->First->NewlinesBefore <= 1 &&
-          NextNonCommentLine->First->OriginalColumn ==
-              (*I)->First->OriginalColumn;
-      if (AlignedWithNextLine)
-        (*I)->Level = NextNonCommentLine->Level;
+    // If the comment is currently aligned with the line immediately following
+    // it, that's probably intentional and we should keep it.
+    if (NextNonCommentLine && CommentLine &&
+        NextNonCommentLine->First->NewlinesBefore <= 1 &&
+        NextNonCommentLine->First->OriginalColumn ==
+            (*I)->First->OriginalColumn) {
+      // Align comments for preprocessor lines with the # in column 0.
+      // Otherwise, align with the next line.
+      (*I)->Level = (NextNonCommentLine->Type == LT_PreprocessorDirective ||
+                     NextNonCommentLine->Type == LT_ImportStatement)
+                        ? 0
+                        : NextNonCommentLine->Level;
     } else {
       NextNonCommentLine = (*I)->First->isNot(tok::r_brace) ? (*I) : nullptr;
     }