[clang-format] Keep level of comment before an empty line

Summary:
This patch fixes bug https://bugs.llvm.org/show_bug.cgi?id=3313: a comment line
was aligned with the next #ifdef even in the presence of an empty line between
them.

Reviewers: djasper, klimek

Reviewed By: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D35296

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@307795 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 4 deletions

diff --git a/lib/Format/TokenAnnotator.cpp b/lib/Format/TokenAnnotator.cpp
index b4d20a7bd6..c6e90a9175 100644
--- a/lib/Format/TokenAnnotator.cpp
+++ b/lib/Format/TokenAnnotator.cpp
@@ -1694,17 +1694,26 @@ void TokenAnnotator::setCommentLineLevels(
   for (SmallVectorImpl<AnnotatedLine *>::reverse_iterator I = Lines.rbegin(),
                                                           E = Lines.rend();
        I != E; ++I) {
-    bool CommentLine = (*I)->First;
+    bool CommentLine = true;
     for (const FormatToken *Tok = (*I)->First; Tok; Tok = Tok->Next) {
       if (!Tok->is(tok::comment)) {
         CommentLine = false;
         break;
       }
     }
-    if (NextNonCommentLine && CommentLine)
-      (*I)->Level = NextNonCommentLine->Level;
-    else
+
+    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;
+    } else {
       NextNonCommentLine = (*I)->First->isNot(tok::r_brace) ? (*I) : nullptr;
+    }
 
     setCommentLineLevels((*I)->Children);
   }