[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, 9 insertions, 0 deletions

diff --git a/clang/lib/Format/BreakableToken.h b/clang/lib/Format/BreakableToken.h
index 630e927e8fc..8c2dc741d1e 100644
--- a/clang/lib/Format/BreakableToken.h
+++ b/clang/lib/Format/BreakableToken.h
@@ -58,6 +58,8 @@ struct FormatStyle;
 /// operations that might be executed before the main line breaking occurs:
 /// - getSplitBefore, for finding a split such that the content preceding it
 ///   needs to be specially reflown,
+/// - introducesBreakBefore, for checking if reformatting the beginning
+///   of the content introduces a line break before it,
 /// - getLineLengthAfterSplitBefore, for calculating the line length in columns
 ///   of the remainder of the content after the beginning of the content has
 ///   been reformatted, and
@@ -135,6 +137,12 @@ public:
     return Split(StringRef::npos, 0);
   }
 
+  /// \brief Returns if a break before the content at \p LineIndex will be
+  /// inserted after the whitespace preceding the content has been reformatted.
+  virtual bool introducesBreakBefore(unsigned LineIndex) const {
+    return false;
+  }
+
   /// \brief Returns the number of columns required to format the piece of line
   /// at \p LineIndex after the content preceding the whitespace range specified
   /// \p SplitBefore has been reformatted, but before any breaks are made to
@@ -339,6 +347,7 @@ public:
   Split getSplitBefore(unsigned LineIndex, unsigned PreviousEndColumn,
                        unsigned ColumnLimit,
                        llvm::Regex &CommentPragmasRegex) const override;
+  bool introducesBreakBefore(unsigned LineIndex) const override;
   unsigned getLineLengthAfterSplitBefore(unsigned LineIndex,
                                          unsigned TailOffset,
                                          unsigned PreviousEndColumn,