[clangd] Serve comments for headers decls from dynamic index only

Summary:
To fix a crash in code completion that occurrs when reading doc
comments from files that were updated after the preamble was
computed. In that case, the files on disk could've been changed and we
can't rely on finding the comment text with the same range anymore.

The current workaround is to not provide comments from the headers at
all and rely on the dynamic index instead.

A more principled solution would be to store contents of the files
read inside the preamble, but it is way harder to implement properly,
given that it would definitely increase the sizes of the preamble.

Together with D47272, this should fix all preamble-related crashes
we're aware of.

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: klimek, ioeric, MaskRay, jkorous, cfe-commits

Differential Revision: https://reviews.llvm.org/D47274

llvm-svn: 333189

1 files changed, 18 insertions, 4 deletions

diff --git a/clang-tools-extra/clangd/CodeCompletionStrings.cpp b/clang-tools-extra/clangd/CodeCompletionStrings.cpp
index cbdd14d1095..f918a54c41c 100644
--- a/clang-tools-extra/clangd/CodeCompletionStrings.cpp
+++ b/clang-tools-extra/clangd/CodeCompletionStrings.cpp
@@ -10,6 +10,7 @@
 #include "CodeCompletionStrings.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RawCommentList.h"
+#include "clang/Basic/SourceManager.h"
 #include <utility>
 
 namespace clang {
@@ -122,10 +123,23 @@ void processSnippetChunks(const CodeCompletionString &CCS,
   }
 }
 
+std::string getFormattedComment(const ASTContext &Ctx, const RawComment &RC,
+                                bool CommentsFromHeaders) {
+  auto &SourceMgr = Ctx.getSourceManager();
+  // Parsing comments from invalid preamble can lead to crashes. So we only
+  // return comments from the main file when doing code completion. For
+  // indexing, we still read all the comments.
+  // FIXME: find a better fix, e.g. store file contents in the preamble or get
+  // doc comments from the index.
+  if (!CommentsFromHeaders && !SourceMgr.isWrittenInMainFile(RC.getLocStart()))
+    return "";
+  return RC.getFormattedText(Ctx.getSourceManager(), Ctx.getDiagnostics());
+}
 } // namespace
 
 std::string getDocComment(const ASTContext &Ctx,
-                          const CodeCompletionResult &Result) {
+                          const CodeCompletionResult &Result,
+                          bool CommentsFromHeaders) {
   // FIXME: clang's completion also returns documentation for RK_Pattern if they
   // contain a pattern for ObjC properties. Unfortunately, there is no API to
   // get this declaration, so we don't show documentation in that case.
@@ -137,20 +151,20 @@ std::string getDocComment(const ASTContext &Ctx,
   const RawComment *RC = getCompletionComment(Ctx, Decl);
   if (!RC)
     return "";
-  return RC->getFormattedText(Ctx.getSourceManager(), Ctx.getDiagnostics());
+  return getFormattedComment(Ctx, *RC, CommentsFromHeaders);
 }
 
 std::string
 getParameterDocComment(const ASTContext &Ctx,
                        const CodeCompleteConsumer::OverloadCandidate &Result,
-                       unsigned ArgIndex) {
+                       unsigned ArgIndex, bool CommentsFromHeaders) {
   auto Func = Result.getFunction();
   if (!Func)
     return "";
   const RawComment *RC = getParameterComment(Ctx, Result, ArgIndex);
   if (!RC)
     return "";
-  return RC->getFormattedText(Ctx.getSourceManager(), Ctx.getDiagnostics());
+  return getFormattedComment(Ctx, *RC, CommentsFromHeaders);
 }
 
 void getLabelAndInsertText(const CodeCompletionString &CCS, std::string *Label,