[clangd] Support parsing comments without ASTContext

This is in preparation for implementing doxygen parsing, see discussion in clangd/clangd#529.

Differential Revision: https://reviews.llvm.org/D143112

Author: tom-anders

clang-tools-extra/clangd/CodeCompletionStrings.cpp

@@ -9,6 +9,9 @@
 #include "CodeCompletionStrings.h"
 #include "clang-c/Index.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/CommentLexer.h"
+#include "clang/AST/CommentParser.h"
+#include "clang/AST/CommentSema.h"
 #include "clang/AST/RawCommentList.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Sema/CodeCompleteConsumer.h"
@@ -316,5 +319,26 @@ std::string getReturnType(const CodeCompletionString &CCS) {
   return "";
 }
 
+comments::FullComment *parseComment(llvm::StringRef Comment,
+                                    llvm::BumpPtrAllocator &Allocator,
+                                    comments::CommandTraits &Traits) {
+  // The comment lexer expects markers, so add them back
+  auto CommentWithMarkers = "/*" + Comment.str() + "*/";
+
+  SourceManagerForFile SourceMgrForFile("mock_file.cpp", CommentWithMarkers);
+  SourceManager &SourceMgr = SourceMgrForFile.get();
+
+  comments::Lexer L(Allocator, SourceMgr.getDiagnostics(), Traits,
+                    SourceMgr.getLocForStartOfFile(SourceMgr.getMainFileID()),
+                    CommentWithMarkers.data(),
+                    CommentWithMarkers.data() + CommentWithMarkers.size());
+  comments::Sema S(Allocator, SourceMgr, SourceMgr.getDiagnostics(), Traits,
+                   nullptr);
+  comments::Parser P(L, S, Allocator, SourceMgr, SourceMgr.getDiagnostics(),
+                     Traits);
+
+  return P.parseFullComment();
+}
+
 } // namespace clangd
 } // namespace clang

clang-tools-extra/clangd/CodeCompletionStrings.h

@@ -19,6 +19,11 @@
 namespace clang {
 class ASTContext;
 
+namespace comments {
+class CommandTraits;
+class FullComment;
+} // namespace comments
+
 namespace clangd {
 
 /// Gets a minimally formatted documentation comment of \p Result, with comment
@@ -67,6 +72,12 @@ std::string formatDocumentation(const CodeCompletionString &CCS,
 /// is usually the return type of a function.
 std::string getReturnType(const CodeCompletionString &CCS);
 
+/// Parse the \p Comment, storing the result in \p Allocator, assuming
+/// that comment markers have already been stripped (e.g. via getDocComment())
+comments::FullComment *parseComment(llvm::StringRef Comment,
+                                    llvm::BumpPtrAllocator &Allocator,
+                                    comments::CommandTraits &Traits);
+
 } // namespace clangd
 } // namespace clang
 

clang/include/clang/Basic/SourceManager.h

@@ -1971,7 +1971,7 @@ class BeforeThanCompare<SourceRange> {
 };
 
 /// SourceManager and necessary dependencies (e.g. VFS, FileManager) for a
-/// single in-memorty file.
+/// single in-memory file.
 class SourceManagerForFile {
 public:
   /// Creates SourceManager and necessary dependencies (e.g. VFS, FileManager).