[AST] Fix an assertion failure in TypeName::getFullyQualifiedName

[ilya-biryukov]

This popped up during our internal integrates of upstream changes. It started happening after ba9d1c4, which started using TemplateSpecializationType in this place and the code was not prepared to handle it.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Ilya Biryukov (ilya-biryukov)

Changes

This popped up during our internal integrates of upstream changes. It started happening after ba9d1c4, which started using TemplateSpecializationType in this place and the code was not prepared to handle it.

---

Full diff: https://github.com/llvm/llvm-project/pull/159312.diff

3 Files Affected:

• (modified) clang/lib/AST/QualTypeNames.cpp (+6-3)
• (modified) clang/unittests/AST/CMakeLists.txt (+1)
• (added) clang/unittests/AST/QualTypeNamesTest.cpp (+55)

diff --git a/clang/lib/AST/QualTypeNames.cpp b/clang/lib/AST/QualTypeNames.cpp
index ee7fec3372fcf..b0e9a600f41a3 100644
--- a/clang/lib/AST/QualTypeNames.cpp
+++ b/clang/lib/AST/QualTypeNames.cpp
@@ -58,9 +58,9 @@ static bool getFullyQualifiedTemplateName(const ASTContext &Ctx,
   NestedNameSpecifier NNS = std::nullopt;
 
   TemplateDecl *ArgTDecl = TName.getAsTemplateDecl();
-  // ArgTDecl won't be NULL because we asserted that this isn't a
-  // dependent context very early in the call chain.
-  assert(ArgTDecl != nullptr);
+  if (!ArgTDecl)  // ArgTDecl can be null in dependent contexts.
+    return false;
+
   QualifiedTemplateName *QTName = TName.getAsQualifiedTemplateName();
 
   if (QTName &&
@@ -252,6 +252,9 @@ createNestedNameSpecifierForScopeOf(const ASTContext &Ctx, const Decl *Decl,
                                     bool WithGlobalNsPrefix) {
   assert(Decl);
 
+  // Some declaration cannot be qualified.
+  if (Decl->isTemplateParameter())
+    return std::nullopt;
   const DeclContext *DC = Decl->getDeclContext()->getRedeclContext();
   const auto *Outer = dyn_cast<NamedDecl>(DC);
   const auto *OuterNS = dyn_cast<NamespaceDecl>(DC);
diff --git a/clang/unittests/AST/CMakeLists.txt b/clang/unittests/AST/CMakeLists.txt
index f27d34e8a0719..3a12a4a06a33a 100644
--- a/clang/unittests/AST/CMakeLists.txt
+++ b/clang/unittests/AST/CMakeLists.txt
@@ -26,6 +26,7 @@ add_clang_unittest(ASTTests
   ExternalASTSourceTest.cpp
   NamedDeclPrinterTest.cpp
   ProfilingTest.cpp
+  QualTypeNamesTest.cpp
   RandstructTest.cpp
   RawCommentForDeclTest.cpp
   RecursiveASTVisitorTest.cpp
diff --git a/clang/unittests/AST/QualTypeNamesTest.cpp b/clang/unittests/AST/QualTypeNamesTest.cpp
new file mode 100644
index 0000000000000..71e4c87cedc72
--- /dev/null
+++ b/clang/unittests/AST/QualTypeNamesTest.cpp
@@ -0,0 +1,55 @@
+//===- unittests/AST/QualTypeNamesTest.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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains tests for helpers from QualTypeNames.h.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/QualTypeNames.h"
+#include "ASTPrint.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/DeclarationName.h"
+#include "clang/AST/TypeBase.h"
+#include "clang/Tooling/Tooling.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Casting.h"
+#include "gtest/gtest.h"
+
+namespace clang {
+namespace {
+
+TEST(QualTypeNamesTest, TemplateParameters) {
+  constexpr llvm::StringLiteral Code = R"cpp(
+    template <template<class> class T> struct Foo {
+      using type_of_interest = T<int>;
+    };
+  )cpp";
+  auto AST = tooling::buildASTFromCode(Code);
+  ASSERT_NE(AST, nullptr);
+
+  auto &Ctx = AST->getASTContext();
+  auto FooLR = Ctx.getTranslationUnitDecl()->lookup(
+      DeclarationName(AST->getPreprocessor().getIdentifierInfo("Foo")));
+  ASSERT_TRUE(FooLR.isSingleResult());
+
+  auto TypeLR =
+      llvm::cast<ClassTemplateDecl>(FooLR.front())
+          ->getTemplatedDecl()
+          ->lookup(DeclarationName(
+              AST->getPreprocessor().getIdentifierInfo("type_of_interest")));
+  ASSERT_TRUE(TypeLR.isSingleResult());
+
+  auto Type = cast<TypeAliasDecl>(TypeLR.front())->getUnderlyingType();
+  ASSERT_TRUE(isa<TemplateSpecializationType>(Type));
+
+  EXPECT_EQ(TypeName::getFullyQualifiedName(Type, Ctx, Ctx.getPrintingPolicy()), "T<int>");
+}
+
+} // namespace
+} // namespace clang

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[rnk]

Thanks Ilya!

[mizvekov]

This looks clearer to me:

Suggested change

	// Some declaration cannot be qualified.
	// Template parameters can't be qualified.

[mizvekov]

Oh I was just about to review, but this looks fine, thanks!