[clang-format] Add comment manipulation header

Summary:
Introduces a separate target for comment manipulation.
Currently, comment manipulation is in BreakableComment.cpp.
Towards implementing comment reflowing, we want to factor out the
comment-related functionality, so it can be reused.
Start simple by just moving out getLineCommentIndentPrefix.

Patch by Krasimir Georgiev!

Reviewers: djasper

Subscribers: klimek, beanz, mgorny, modocache

Differential Revision: https://reviews.llvm.org/D25725

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@284573 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/BreakableToken.cpp

@@ -14,6 +14,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "BreakableToken.h"
+#include "Comments.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Format/Format.h"
 #include "llvm/ADT/STLExtras.h"
@@ -182,21 +183,6 @@ void BreakableStringLiteral::insertBreak(unsigned LineIndex,
       Prefix, InPPDirective, 1, IndentLevel, LeadingSpaces);
 }
 
-static StringRef getLineCommentIndentPrefix(StringRef Comment) {
-  static const char *const KnownPrefixes[] = {"///", "//", "//!"};
-  StringRef LongestPrefix;
-  for (StringRef KnownPrefix : KnownPrefixes) {
-    if (Comment.startswith(KnownPrefix)) {
-      size_t PrefixLength = KnownPrefix.size();
-      while (PrefixLength < Comment.size() && Comment[PrefixLength] == ' ')
-        ++PrefixLength;
-      if (PrefixLength > LongestPrefix.size())
-        LongestPrefix = Comment.substr(0, PrefixLength);
-    }
-  }
-  return LongestPrefix;
-}
-
 BreakableLineComment::BreakableLineComment(
     const FormatToken &Token, unsigned IndentLevel, unsigned StartColumn,
     bool InPPDirective, encoding::Encoding Encoding, const FormatStyle &Style)

lib/Format/CMakeLists.txt

@@ -3,6 +3,7 @@ set(LLVM_LINK_COMPONENTS support)
 add_clang_library(clangFormat
   AffectedRangeManager.cpp
   BreakableToken.cpp
+  Comments.cpp
   ContinuationIndenter.cpp
   Format.cpp
   FormatToken.cpp

lib/Format/Comments.cpp

+//===--- Comments.cpp - Comment Manipulation  -------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief Implements comment manipulation.
+///
+//===----------------------------------------------------------------------===//
+
+#include "Comments.h"
+
+namespace clang {
+namespace format {
+
+StringRef getLineCommentIndentPrefix(StringRef Comment) {
+  static const char *const KnownPrefixes[] = {"///", "//", "//!"};
+  StringRef LongestPrefix;
+  for (StringRef KnownPrefix : KnownPrefixes) {
+    if (Comment.startswith(KnownPrefix)) {
+      size_t PrefixLength = KnownPrefix.size();
+      while (PrefixLength < Comment.size() && Comment[PrefixLength] == ' ')
+        ++PrefixLength;
+      if (PrefixLength > LongestPrefix.size())
+        LongestPrefix = Comment.substr(0, PrefixLength);
+    }
+  }
+  return LongestPrefix;
+}
+
+} // namespace format
+} // namespace clang

lib/Format/Comments.h

+//===--- Comments.cpp - Comment manipulation  -----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief Declares comment manipulation functionality.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_LIB_FORMAT_COMMENTS_H
+#define LLVM_CLANG_LIB_FORMAT_COMMENTS_H
+
+#include "clang/Basic/LLVM.h"
+#include "llvm/ADT/StringRef.h"
+
+namespace clang {
+namespace format {
+
+/// \brief Returns the comment prefix of the line comment \p Comment.
+///
+/// The comment prefix consists of a leading known prefix, like "//" or "///",
+/// together with the following whitespace.
+StringRef getLineCommentIndentPrefix(StringRef Comment);
+
+} // namespace format
+} // namespace clang
+
+#endif