[clang-format] Fix reflow in block comment lines with leading whitespace.

Summary:
The reflower was not taking into account the additional  leading whitespace in block comment lines.

source:
```
{
/*
 * long long long long
 *   long
 * long long long long
 */
}
```

format (with column limit 20) before:
```
{
  /*
   * long long long
   * long long long long
   * long long
   */
}
```
format after:
```
{
  /*
   * long long long
   * long long long
   * long long long
   */
}
```

Reviewers: djasper, klimek

Reviewed By: djasper

Subscribers: cfe-commits, sammccall, klimek

Differential Revision: https://reviews.llvm.org/D29326

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@293633 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 4 deletions

diff --git a/lib/Format/BreakableToken.cpp b/lib/Format/BreakableToken.cpp
index 82e62ac80f..683d6e7249 100644
--- a/lib/Format/BreakableToken.cpp
+++ b/lib/Format/BreakableToken.cpp
@@ -521,10 +521,15 @@ unsigned BreakableBlockComment::getLineLengthAfterSplitBefore(
     unsigned PreviousEndColumn,
     unsigned ColumnLimit,
     Split SplitBefore) const {
-    if (SplitBefore.first == StringRef::npos ||
-        SplitBefore.first + SplitBefore.second < Content[LineIndex].size()) {
-      // A piece of line, not the whole, gets reflown.
-      return getLineLengthAfterSplit(LineIndex, TailOffset, StringRef::npos);
+  if (SplitBefore.first == StringRef::npos ||
+      // Block comment line contents contain the trailing whitespace after the
+      // decoration, so the need of left trim. Note that this behavior is
+      // consistent with the breaking of block comments where the indentation of
+      // a broken line is uniform across all the lines of the block comment.
+      SplitBefore.first + SplitBefore.second <
+          Content[LineIndex].ltrim().size()) {
+    // A piece of line, not the whole, gets reflown.
+    return getLineLengthAfterSplit(LineIndex, TailOffset, StringRef::npos);
   } else {
     // The whole line gets reflown, need to check if we need to insert a break
     // for the postfix or not.