[clangd] Drop documentation in static index if symbols are not indexed for completion.

[hokein]

Summary

This is a further optimization of r350803, we drop docs in static index for
symbols not being indexed for completion, while keeping the docs in dynamic
index (we rely on dynamic index to get docs for class members).

[ilya-biryukov]

Just realized I missed this review, sorry about that.
LGTM with a nit.

clangd/index/FileIndex.cpp

51

NIT: maybe mention the rationale here in a comment? Something like // comments for main file can always be obtained from sema, do not store them in the index.

[hokein]

Rebase and address comment.

clangd/index/FileIndex.cpp

indexSymbols(ASTContext &AST, std::shared_ptr<Preprocessor> PP,
   index::IndexingOptions IndexOpts;
   // We only need declarations, because we don't count references.
   IndexOpts.SystemSymbolFilter =
       index::IndexingOptions::SystemSymbolFilterKind::DeclarationsOnly;
   IndexOpts.IndexFunctionLocals = false;
   if (IsIndexMainAST) {
     // We only collect refs when indexing main AST.
     CollectorOpts.RefFilter = RefKind::All;
+    // Comments for main file can always be obtained from sema, do not store
+    // them in the index.
+    CollectorOpts.StoreAllDocumentation = false;
   } else {
     IndexOpts.IndexMacrosInPreprocessor = true;
     CollectorOpts.CollectMacro = true;
+    CollectorOpts.StoreAllDocumentation = true;
   }
 
   SymbolCollector Collector(std::move(CollectorOpts));
   Collector.setPreprocessor(PP);
   index::indexTopLevelDecls(AST, *PP, DeclsToIndex, Collector, IndexOpts);
 
   const auto &SM = AST.getSourceManager();
   const auto *MainFileEntry = SM.getFileEntryForID(SM.getMainFileID());

clangd/index/IndexAction.cpp

std::unique_ptr<FrontendAction> createStaticIndexingAction(
     std::function<void(RefSlab)> RefsCallback,
     std::function<void(IncludeGraph)> IncludeGraphCallback) {
   index::IndexingOptions IndexOpts;
   IndexOpts.SystemSymbolFilter =
       index::IndexingOptions::SystemSymbolFilterKind::All;
   Opts.CollectIncludePath = true;
   Opts.CountReferences = true;
   Opts.Origin = SymbolOrigin::Static;
+  Opts.StoreAllDocumentation = false;
   if (RefsCallback != nullptr) {
     Opts.RefFilter = RefKind::All;
     Opts.RefsInHeaders = true;
   }
   auto Includes = llvm::make_unique<CanonicalIncludes>();
   addSystemHeadersMapping(Includes.get());
   Opts.Includes = Includes.get();
   return llvm::make_unique<IndexAction>(
       std::make_shared<SymbolCollector>(std::move(Opts)), std::move(Includes),
       IndexOpts, SymbolsCallback, RefsCallback, IncludeGraphCallback);
 }
 
 } // namespace clangd
 } // namespace clang

clangd/index/SymbolCollector.h

struct Options {
     /// Collect macros.
     /// Note that SymbolCollector must be run with preprocessor in order to
     /// collect macros. For example, `indexTopLevelDecls` will not index any
     /// macro even if this is true.
     bool CollectMacro = false;
     /// Collect symbols local to main-files, such as static functions
     /// and symbols inside an anonymous namespace.
     bool CollectMainFileSymbols = true;
+    /// If set to true, SymbolCollector will collect doc for all symbols.
+    /// Note that documents of symbols being indexed for completion will always
+    /// be collected regardless of this option.
+    bool StoreAllDocumentation = false;
     /// If this is set, only collect symbols/references from a file if
     /// `FileFilter(SM, FID)` is true. If not set, all files are indexed.
     std::function<bool(const SourceManager &, FileID)> FileFilter = nullptr;
   };
 
   SymbolCollector(Options Opts);
 
   /// Returns true is \p ND should be collected.

clangd/index/SymbolCollector.cpp

const Symbol *SymbolCollector::addDeclaration(const NamedDecl &ND,
   CodeCompletionResult SymbolCompletion(&getTemplateOrThis(ND), 0);
   const auto *CCS = SymbolCompletion.CreateCodeCompletionString(
       *ASTCtx, *PP, CodeCompletionContext::CCC_Symbol, *CompletionAllocator,
       *CompletionTUInfo,
       /*IncludeBriefComments*/ false);
   std::string Documentation =
       formatDocumentation(*CCS, getDocComment(Ctx, SymbolCompletion,
                                               /*CommentsFromHeaders=*/true));
-  // For symbols not indexed for completion (class members), we also store their
-  // docs in the index, because Sema doesn't load the docs from the preamble, we
-  // rely on the index to get the docs.
-  // FIXME: this can be optimized by only storing the docs in dynamic index --
-  // dynamic index should index these symbols when Sema completes a member
-  // completion.
-  S.Documentation = Documentation;
   if (!(S.Flags & Symbol::IndexedForCodeCompletion)) {
+    if (Opts.StoreAllDocumentation)
+      S.Documentation = Documentation;
     Symbols.insert(S);
     return Symbols.find(S.ID);
   }
-
+  S.Documentation = Documentation;
   std::string Signature;
   std::string SnippetSuffix;
   getSignature(*CCS, &Signature, &SnippetSuffix);
   S.Signature = Signature;
   S.CompletionSnippetSuffix = SnippetSuffix;
   std::string ReturnType = getReturnType(*CCS);
   S.ReturnType = ReturnType;
 

unittests/clangd/SymbolCollectorTests.cpp

public:
 
       std::unique_ptr<ASTConsumer>
       CreateASTConsumer(CompilerInstance &CI, llvm::StringRef InFile) override {
         if (PragmaHandler)
           CI.getPreprocessor().addCommentHandler(PragmaHandler);
         return WrapperFrontendAction::CreateASTConsumer(CI, InFile);
       }
 
+      bool BeginInvocation(CompilerInstance &CI) override {
+        // Make the compiler parse all comments.
+        CI.getLangOpts().CommentOpts.ParseAllComments = true;
+        return WrapperFrontendAction::BeginInvocation(CI);
+      }
+
     private:
       index::IndexingOptions IndexOpts;
       CommentHandler *PragmaHandler;
     };
     index::IndexingOptions IndexOpts;
     IndexOpts.SystemSymbolFilter =
         index::IndexingOptions::SystemSymbolFilterKind::All;
     IndexOpts.IndexFunctionLocals = false;
TEST_F(SymbolCollectorTest, SymbolsInMainFile) {
   )";
   runSymbolCollector(/*Header=*/"", Main);
   EXPECT_THAT(Symbols,
               UnorderedElementsAre(QName("Foo"), QName("f1"), QName("f2"),
                                    QName("ff"), QName("foo"), QName("foo::Bar"),
                                    QName("main_f")));
 }
 
+TEST_F(SymbolCollectorTest, Documentation) {
+  const std::string Header = R"(
+    // Doc Foo
+    class Foo {
+      // Doc f
+      int f();
+    };
+  )";
+  CollectorOpts.StoreAllDocumentation = false;
+  runSymbolCollector(Header, /* Main */ "");
+  EXPECT_THAT(Symbols,
+              UnorderedElementsAre(
+                  AllOf(QName("Foo"), Doc("Doc Foo"), ForCodeCompletion(true)),
+                  AllOf(QName("Foo::f"), Doc(""), ReturnType(""),
+                        ForCodeCompletion(false))));
+
+  CollectorOpts.StoreAllDocumentation = true;
+  runSymbolCollector(Header, /* Main */ "");
+  EXPECT_THAT(Symbols,
+              UnorderedElementsAre(
+                  AllOf(QName("Foo"), Doc("Doc Foo"), ForCodeCompletion(true)),
+                  AllOf(QName("Foo::f"), Doc("Doc f"), ReturnType(""),
+                        ForCodeCompletion(false))));
+}
+
 TEST_F(SymbolCollectorTest, ClassMembers) {
   const std::string Header = R"(
     class Foo {
       void f() {}
       void g();
       static void sf() {}
       static void ssf();
       static int x;