[PATCH] D48943: [clangd] Do not write comments into Preamble PCH

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov created this revision.
ilya-biryukov added a reviewer: sammccall.
Herald added subscribers: jkorous, MaskRay, ioeric.

To avoid wasting time deserializing them on code completion and
further reparses.

We do not use the comments anyway, because we cannot rely on the file
contents staying the same for reparses that reuse the prebuilt
preamble PCH.


Repository:
  rCTE Clang Tools Extra

https://reviews.llvm.org/D48943

Files:
  clangd/ClangdUnit.cpp
  clangd/CodeCompletionStrings.cpp


Index: clangd/CodeCompletionStrings.cpp
===================================================================
--- clangd/CodeCompletionStrings.cpp
+++ clangd/CodeCompletionStrings.cpp
@@ -32,34 +32,6 @@
   }
 }
 
-bool canRequestComment(const ASTContext &Ctx, const NamedDecl &D,
-                       bool CommentsFromHeaders) {
-  if (CommentsFromHeaders)
-    return true;
-  auto &SourceMgr = Ctx.getSourceManager();
-  // Accessing comments for decls 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.
-  auto canRequestForDecl = [&](const NamedDecl &D) -> bool {
-    for (auto *Redecl : D.redecls()) {
-      auto Loc = SourceMgr.getSpellingLoc(Redecl->getLocation());
-      if (!SourceMgr.isWrittenInMainFile(Loc))
-        return false;
-    }
-    return true;
-  };
-  // First, check the decl itself.
-  if (!canRequestForDecl(D))
-    return false;
-  // Completion also returns comments for properties, corresponding to ObjC
-  // methods.
-  const ObjCMethodDecl *M = dyn_cast<ObjCMethodDecl>(&D);
-  const ObjCPropertyDecl *PDecl = M ? M->findPropertyDecl() : nullptr;
-  return !PDecl || canRequestForDecl(*PDecl);
-}
-
 bool LooksLikeDocComment(llvm::StringRef CommentText) {
   // We don't report comments that only contain "special" chars.
   // This avoids reporting various delimiters, like:
@@ -87,12 +59,13 @@
     // the comments for namespaces.
     return "";
   }
-  if (!canRequestComment(Ctx, *Decl, CommentsFromHeaders))
-    return "";
-
   const RawComment *RC = getCompletionComment(Ctx, Decl);
   if (!RC)
     return "";
+
+  // Sanity check that the comment does not come from the PCH. We choose to not
+  // write them into PCH, because they are racy and slow to load.
+  assert(!Ctx.getSourceManager().isLoadedSourceLocation(RC->getLocStart()));
   std::string Doc = RC->getFormattedText(Ctx.getSourceManager(), Ctx.getDiagnostics());
   if (!LooksLikeDocComment(Doc))
     return "";
@@ -104,11 +77,14 @@
                        const CodeCompleteConsumer::OverloadCandidate &Result,
                        unsigned ArgIndex, bool CommentsFromHeaders) {
   auto *Func = Result.getFunction();
-  if (!Func || !canRequestComment(Ctx, *Func, CommentsFromHeaders))
+  if (!Func)
     return "";
   const RawComment *RC = getParameterComment(Ctx, Result, ArgIndex);
   if (!RC)
     return "";
+  // Sanity check that the comment does not come from the PCH. We choose to not
+  // write them into PCH, because they are racy and slow to load.
+  assert(!Ctx.getSourceManager().isLoadedSourceLocation(RC->getLocStart()));
   std::string Doc = RC->getFormattedText(Ctx.getSourceManager(), Ctx.getDiagnostics());
   if (!LooksLikeDocComment(Doc))
     return "";
Index: clangd/ClangdUnit.cpp
===================================================================
--- clangd/ClangdUnit.cpp
+++ clangd/ClangdUnit.cpp
@@ -24,6 +24,7 @@
 #include "clang/Lex/Lexer.h"
 #include "clang/Lex/MacroInfo.h"
 #include "clang/Lex/Preprocessor.h"
+#include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Serialization/ASTWriter.h"
 #include "clang/Tooling/CompilationDatabase.h"
@@ -323,6 +324,9 @@
   // the preamble and make it smaller.
   assert(!CI.getFrontendOpts().SkipFunctionBodies);
   CI.getFrontendOpts().SkipFunctionBodies = true;
+  // We don't want to write comments into PCH. They are racy and slow to read
+  // back. We rely on dynamic index for the comments instead.
+  CI.getPreprocessorOpts().WriteCommentListToPCH = false;
 
   CppFilePreambleCallbacks SerializedDeclsCollector(FileName, PreambleCallback);
   if (Inputs.FS->setCurrentWorkingDirectory(Inputs.CompileCommand.Directory)) {


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