[AST] Ensure getRawCommentsForAnyRedecl() does not miss any redecl with a comment

clang/docs/ReleaseNotes.rst

@@ -408,6 +408,8 @@ Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 - Fixed a crash that occurred when dividing by zero in complex integer division. (#GH55390).
+- Fixed a bug in ``ASTContext::getRawCommentForAnyRedecl()`` where the function could
+  sometimes incorrectly return null even if a comment was present. (#GH108145)
 
 Miscellaneous Bug Fixes
 ^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/AST/ASTContext.cpp

@@ -440,12 +440,26 @@ const RawComment *ASTContext::getRawCommentForAnyRedecl(
   }
 
   // Any redeclarations of D that we haven't checked for comments yet?
-  // We can't use DenseMap::iterator directly since it'd get invalid.
-  auto LastCheckedRedecl = [this, CanonicalD]() -> const Decl * {
-    return CommentlessRedeclChains.lookup(CanonicalD);
+  const Decl *LastCheckedRedecl = [&]() {
+    const Decl *LastChecked = CommentlessRedeclChains.lookup(CanonicalD);
+    bool CanUseCommentlessCache = false;
+    if (LastChecked) {
+      for (auto *Redecl : CanonicalD->redecls()) {
+        if (Redecl == D) {
+          CanUseCommentlessCache = true;
+          break;
+        }
+        if (Redecl == LastChecked)
+          break;
+      }
+    }
+    // FIXME: This could be improved so that even if CanUseCommentlessCache
+    // is false, once we've traversed past CanonicalD we still skip ahead
+    // LastChecked.
+    return CanUseCommentlessCache ? LastChecked : nullptr;
   }();
 
-  for (const auto Redecl : D->redecls()) {
+  for (const Decl *Redecl : D->redecls()) {
     assert(Redecl);
     // Skip all redeclarations that have been checked previously.
     if (LastCheckedRedecl) {

clang/unittests/AST/CMakeLists.txt

@@ -34,6 +34,7 @@ add_clang_unittest(ASTTests
   NamedDeclPrinterTest.cpp
   ProfilingTest.cpp
   RandstructTest.cpp
+  RawCommentForDeclTest.cpp
   RecursiveASTVisitorTest.cpp
   SizelessTypesTest.cpp
   SourceLocationTest.cpp

clang/unittests/AST/RawCommentForDeclTest.cpp

@@ -0,0 +1,98 @@
+//===- unittests/AST/RawCommentForDeclTestTest.cpp
+//-------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/ASTConsumer.h"
+#include "clang/AST/DeclGroup.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/FrontendAction.h"
+#include "clang/Tooling/Tooling.h"
+
+#include "gmock/gmock-matchers.h"
+#include "gtest/gtest.h"
+
+namespace clang {
+
+struct FoundComment {
+  std::string DeclName;
+  bool IsDefinition;
+  std::string Comment;
+
+  bool operator==(const FoundComment &RHS) const {
+    return DeclName == RHS.DeclName && IsDefinition == RHS.IsDefinition &&
+           Comment == RHS.Comment;
+  }
+  friend llvm::raw_ostream &operator<<(llvm::raw_ostream &Stream,
+                                       const FoundComment &C) {
+    return Stream << "{Name: " << C.DeclName << ", Def: " << C.IsDefinition
+                  << ", Comment: " << C.Comment << "}";
+  }
+};
+
+class CollectCommentsAction : public ASTFrontendAction {
+public:
+  CollectCommentsAction(std::vector<FoundComment> &Comments)
+      : Comments(Comments) {}
+
+  std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
+                                                 llvm::StringRef) override {
+    CI.getLangOpts().CommentOpts.ParseAllComments = true;
+    return std::make_unique<Consumer>(*this);
+  }
+
+  std::vector<FoundComment> &Comments;
+
+private:
+  class Consumer : public clang::ASTConsumer {
+  private:
+    CollectCommentsAction &Action;
+
+  public:
+    Consumer(CollectCommentsAction &Action) : Action(Action) {}
+
+    bool HandleTopLevelDecl(DeclGroupRef DG) override {
+      for (Decl *D : DG) {
+        if (NamedDecl *ND = dyn_cast<NamedDecl>(D)) {
+          auto &Ctx = D->getASTContext();
+          const auto *RC = Ctx.getRawCommentForAnyRedecl(D);
+          Action.Comments.push_back(FoundComment{
+              ND->getNameAsString(), IsDefinition(D),
+              RC ? RC->getRawText(Ctx.getSourceManager()).str() : ""});
+        }
+      }
+
+      return true;
+    }
+
+    static bool IsDefinition(const Decl *D) {
+      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+        return FD->isThisDeclarationADefinition();
+      }
+      if (const TagDecl *TD = dyn_cast<TagDecl>(D)) {
+        return TD->isThisDeclarationADefinition();
+      }
+      return false;
+    }
+  };
+};
+
+TEST(RawCommentForDecl, DefinitionComment) {
+  std::vector<FoundComment> Comments;
+  auto Action = std::make_unique<CollectCommentsAction>(Comments);
+  ASSERT_TRUE(tooling::runToolOnCode(std::move(Action), R"cpp(
+    void f();
+
+    // f is the best
+    void f() {}
+  )cpp"));
+  EXPECT_THAT(Comments, testing::ElementsAre(
+                            FoundComment{"f", false, ""},
+                            FoundComment{"f", true, "// f is the best"}));
+}
+
+} // namespace clang