[clang-format] Break non-trailing block comments

Summary:
This patch is an alternative to https://reviews.llvm.org/D36614, by resolving a
non-idempotency issue by breaking non-trailing comments:

Consider formatting the following code with column limit at `V`:
```
                    V
const /* comment comment */ A = B;
```
The comment is not a trailing comment, breaking before it doesn't bring it under
the column limit. The formatter breaks after it, resulting in:

```
                    V
const /* comment comment */
    A = B;
```
For a next reformat, the formatter considers the comment as a trailing comment,
so it is free to break it further, resulting in:

```
                    V
const /* comment
         comment */
    A = B;
```
This patch improves the situation by directly producing the third case.

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D37007

llvm-svn: 311457

1 files changed, 16 insertions, 0 deletions

diff --git a/clang/unittests/Format/FormatTestComments.cpp b/clang/unittests/Format/FormatTestComments.cpp
index d1cf10bffca..ffcfb3cfe8b 100644
--- a/clang/unittests/Format/FormatTestComments.cpp
+++ b/clang/unittests/Format/FormatTestComments.cpp
@@ -2780,6 +2780,22 @@ TEST_F(FormatTestComments, AlignsBlockCommentDecorations) {
                    "* long */",
                    getLLVMStyleWithColumns(20)));
 }
+
+TEST_F(FormatTestComments, NonTrailingBlockComments) {
+  verifyFormat("const /** comment comment */ A = B;",
+               getLLVMStyleWithColumns(40));
+
+  verifyFormat("const /** comment comment comment */ A =\n"
+               "    B;",
+               getLLVMStyleWithColumns(40));
+
+  EXPECT_EQ("const /** comment comment comment\n"
+            "         comment */\n"
+            "    A = B;",
+            format("const /** comment comment comment comment */\n"
+                   "    A = B;",
+                   getLLVMStyleWithColumns(40)));
+}
 } // end namespace
 } // end namespace format
 } // end namespace clang