[clangd] Collect comments from function definitions into the index

This is useful with projects that put their (doxygen) comments at the
implementation site, rather than the header.

Author: ckandeler

clang-tools-extra/clangd/index/Symbol.h

@@ -75,7 +75,9 @@ struct Symbol {
   /// (When snippets are disabled, the symbol name alone is used).
   /// Only set when the symbol is indexed for completion.
   llvm::StringRef CompletionSnippetSuffix;
-  /// Documentation including comment for the symbol declaration.
+  /// Comment for the symbol declaration.
+  llvm::StringRef DocComment;
+  /// Documentation including DocComment.
   llvm::StringRef Documentation;
   /// Type when this symbol is used in an expression. (Short display form).
   /// e.g. return type of a function, or type of a variable.

clang-tools-extra/clangd/index/SymbolCollector.cpp

@@ -1016,15 +1016,16 @@ const Symbol *SymbolCollector::addDeclaration(const NamedDecl &ND, SymbolID ID,
       *ASTCtx, *PP, CodeCompletionContext::CCC_Symbol, *CompletionAllocator,
       *CompletionTUInfo,
       /*IncludeBriefComments*/ false);
-  std::string Documentation =
-      formatDocumentation(*CCS, getDocComment(Ctx, SymbolCompletion,
-                                              /*CommentsFromHeaders=*/true));
+  std::string DocComment = getDocComment(Ctx, SymbolCompletion,
+                                         /*CommentsFromHeaders=*/true);
+  std::string Documentation = formatDocumentation(*CCS, DocComment);
   if (!(S.Flags & Symbol::IndexedForCodeCompletion)) {
     if (Opts.StoreAllDocumentation)
       S.Documentation = Documentation;
     Symbols.insert(S);
     return Symbols.find(S.ID);
   }
+  S.DocComment = DocComment;
   S.Documentation = Documentation;
   std::string Signature;
   std::string SnippetSuffix;
@@ -1065,6 +1066,26 @@ void SymbolCollector::addDefinition(const NamedDecl &ND,
   Symbol S = DeclSym;
   // FIXME: use the result to filter out symbols.
   S.Definition = *DefLoc;
+
+  std::string DocComment;
+  std::string Documentation;
+  if (S.DocComment.empty() &&
+      (llvm::isa<FunctionDecl>(ND) || llvm::isa<CXXMethodDecl>(ND))) {
+    CodeCompletionResult SymbolCompletion(&getTemplateOrThis(ND), 0);
+    const auto *CCS = SymbolCompletion.CreateCodeCompletionString(
+        *ASTCtx, *PP, CodeCompletionContext::CCC_Symbol, *CompletionAllocator,
+        *CompletionTUInfo,
+        /*IncludeBriefComments*/ false);
+    DocComment = getDocComment(ND.getASTContext(), SymbolCompletion,
+                               /*CommentsFromHeaders=*/true);
+    if (!S.Documentation.empty())
+      Documentation = S.Documentation.str() + '\n' + DocComment;
+    else
+      Documentation = formatDocumentation(*CCS, DocComment);
+    S.DocComment = DocComment;
+    S.Documentation = Documentation;
+  }
+
   Symbols.insert(S);
 }
 

clang/lib/AST/ASTContext.cpp

@@ -509,8 +509,17 @@ const RawComment *ASTContext::getRawCommentForAnyRedecl(
     if (LastCheckedRedecl) {
       if (LastCheckedRedecl == Redecl) {
         LastCheckedRedecl = nullptr;
+        continue;
+      }
+      if (auto F = llvm::dyn_cast<FunctionDecl>(Redecl)) {
+        if (!F->isThisDeclarationADefinition())
+          continue;
+      } else if (auto M = llvm::dyn_cast<CXXMethodDecl>(Redecl)) {
+        if (!M->isThisDeclarationADefinition())
+          continue;
+      } else {
+        continue;
       }
-      continue;
     }
     const RawComment *RedeclComment = getRawCommentForDeclNoCache(Redecl);
     if (RedeclComment) {