[clang-format] Break non-trailing comments, try 2

Summary:
This patch enables `BreakableToken` to manage the formatting of non-trailing
block comments. It is a refinement of https://reviews.llvm.org/D37007.
We discovered that the optimizer outsmarts us on cases where breaking the comment
costs considerably less than breaking after the comment. This patch addresses
this by ensuring that a newline is inserted between a block comment and the next
token.

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D37695

llvm-svn: 315893

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/lib/Format/BreakableToken.cpp b/clang/lib/Format/BreakableToken.cpp
index 8031ab9cd28..bbf3d88eec4 100644
--- a/clang/lib/Format/BreakableToken.cpp
+++ b/clang/lib/Format/BreakableToken.cpp
@@ -599,6 +599,12 @@ unsigned BreakableBlockComment::getLineLengthAfterSplitBefore(
   }
 }
 
+bool BreakableBlockComment::introducesBreakBefore(unsigned LineIndex) const {
+  // A break is introduced when we want delimiters on newline.
+  return LineIndex == 0 && DelimitersOnNewline &&
+         Lines[0].substr(1).find_first_not_of(Blanks) != StringRef::npos;
+}
+
 void BreakableBlockComment::replaceWhitespaceBefore(
     unsigned LineIndex, unsigned PreviousEndColumn, unsigned ColumnLimit,
     Split SplitBefore, WhitespaceManager &Whitespaces) {