[clang] fix runtime check listing types which can appear in a NestedNameSpecifier

[mizvekov]

Through alias templates, followed by canonicalization, any canonical dependent type can appear in a NestedNameSpecifier. Remove the list as a practical matter.

This fixes a regression reported here: #147835 (comment)

Since the regression was never released, there are no release notes.

Fixes #155260

[llvmbot]

@llvm/pr-subscribers-clang

Author: Matheus Izvekov (mizvekov)

Changes

Through alias templates, followed by canonicalization, any canonical dependent type can appear in a NestedNameSpecifier. Remove the list as a practical matter.

This fixes a regression reported here: #147835 (comment)

Since the regression was never released, there are no release notes.

---

Full diff: https://github.com/llvm/llvm-project/pull/155272.diff

2 Files Affected:

• (modified) clang/lib/Sema/TreeTransform.h (+3-14)
• (modified) clang/test/SemaTemplate/nested-name-spec-template.cpp (+13-8)

diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 1d14ead778446..87550614f645b 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -5539,21 +5539,10 @@ QualType TreeTransform<Derived>::TransformTypeInObjectScope(
         TLB, TL.castAs<DependentNameTypeLoc>(), /*DeducedTSTContext=*/false,
         ObjectType, UnqualLookup);
   }
-  case TypeLoc::Typedef:
-  case TypeLoc::TemplateSpecialization:
-  case TypeLoc::SubstTemplateTypeParm:
-  case TypeLoc::SubstTemplateTypeParmPack:
-  case TypeLoc::PackIndexing:
-  case TypeLoc::Enum:
-  case TypeLoc::Record:
-  case TypeLoc::InjectedClassName:
-  case TypeLoc::TemplateTypeParm:
-  case TypeLoc::Decltype:
-  case TypeLoc::UnresolvedUsing:
-  case TypeLoc::Using:
-    return getDerived().TransformType(TLB, TL);
   default:
-    llvm_unreachable("unexpected type class");
+    // Any dependent canonical type can appear here, through type alias
+    // templates.
+    return getDerived().TransformType(TLB, TL);
   }
 }
 
diff --git a/clang/test/SemaTemplate/nested-name-spec-template.cpp b/clang/test/SemaTemplate/nested-name-spec-template.cpp
index 153f4e2555e3a..0f51a14af9e52 100644
--- a/clang/test/SemaTemplate/nested-name-spec-template.cpp
+++ b/clang/test/SemaTemplate/nested-name-spec-template.cpp
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -Wno-c++20-extensions
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c++98 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-c++11-extensions -std=c++98 %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
 
 namespace N {
@@ -24,14 +24,7 @@ namespace N {
 
   M::Promote<int>::type *ret_intptr3(int* ip) { return ip; }
   M::template Promote<int>::type *ret_intptr4(int* ip) { return ip; }
-#if __cplusplus <= 199711L
-  // expected-warning@-2 {{'template' keyword outside of a template}}
-#endif
-
   M::template Promote<int> pi;
-#if __cplusplus <= 199711L
-  // expected-warning@-2 {{'template' keyword outside of a template}}
-#endif
 }
 
 N::M::Promote<int>::type *ret_intptr5(int* ip) { return ip; }
@@ -181,3 +174,15 @@ namespace SubstTemplateTypeParmPackType {
   template void f<B>();
 } // namespace SubstTemplateTypeParmPackType
 #endif
+
+namespace DependentUnaryTransform {
+  template <class T> using decay_t = __decay(T);
+  template <class, class> struct A;
+  template <class T> struct A<T, typename decay_t<T>::X>;
+} // namespace DependentUnaryTransform
+
+namespace DependentSizedArray {
+  template <int V> using Z = int[V];
+  template <class, class> struct A;
+  template <class T> struct A<T, typename Z<T(0)>::X>;
+} // namespace DependentUnaryTransform

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clangd-ubuntu-tsan running on clangd-ubuntu-clang while building clang at step 6 "test-build-clangd-clangd-index-server-clangd-in...".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/134/builds/25080

Here is the relevant piece of the build log for the reference

Step 6 (test-build-clangd-clangd-index-server-clangd-in...) failure: test (failure)
******************** TEST 'Clangd :: inlayHints.test' FAILED ********************
Exit Code: 66

Command Output (stderr):
--
clangd -lit-test < /vol/worker/clangd-ubuntu-clang/clangd-ubuntu-tsan/llvm-project/clang-tools-extra/clangd/test/inlayHints.test | /vol/worker/clangd-ubuntu-clang/clangd-ubuntu-tsan/build/bin/FileCheck /vol/worker/clangd-ubuntu-clang/clangd-ubuntu-tsan/llvm-project/clang-tools-extra/clangd/test/inlayHints.test # RUN: at line 1
+ clangd -lit-test
+ /vol/worker/clangd-ubuntu-clang/clangd-ubuntu-tsan/build/bin/FileCheck /vol/worker/clangd-ubuntu-clang/clangd-ubuntu-tsan/llvm-project/clang-tools-extra/clangd/test/inlayHints.test
WARNING: ThreadSanitizer: unexpected memory mapping 0x79ffffc72000-0x7a0000100000
FATAL: ThreadSanitizer: unexpectedly found incompatible memory layout.
FATAL: Please file a bug.
I[18:43:29.460] clangd version 22.0.0git (https://github.com/llvm/llvm-project.git f941769a8af61159e27f5598f1dffaab6f7b0fbb)
I[18:43:29.461] Features: linux+debug+tsan+grpc
I[18:43:29.461] PID: 16345
I[18:43:29.461] Working directory: /vol/worker/clangd-ubuntu-clang/clangd-ubuntu-tsan/build/tools/clang/tools/extra/clangd/test
I[18:43:29.461] argv[0]: clangd
I[18:43:29.461] argv[1]: -lit-test
I[18:43:29.461] Starting LSP over stdin/stdout
V[18:43:29.461] <<< {
  "id": 0,
  "jsonrpc": "2.0",
  "method": "initialize",
  "params": {}
}

I[18:43:29.461] <-- initialize(0)
I[18:43:29.462] --> reply:initialize(0) 1 ms

--

********************