Fix crash in constraining partial specialization on nested template.

Fixes: https://github.com/llvm/llvm-project/issues/53354

Differential Revision: https://reviews.llvm.org/D136259

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 0572a66..a731ff6 100644 (file)
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -5803,8 +5803,8 @@ struct MarkUsedTemplateParameterVisitor :
   }
 
   bool TraverseTemplateName(TemplateName Template) {
-    if (auto *TTP =
-            dyn_cast<TemplateTemplateParmDecl>(Template.getAsTemplateDecl()))
+    if (auto *TTP = llvm::dyn_cast_or_null<TemplateTemplateParmDecl>(
+            Template.getAsTemplateDecl()))
       if (TTP->getDepth() == Depth)
         Used[TTP->getIndex()] = true;
     RecursiveASTVisitor<MarkUsedTemplateParameterVisitor>::

diff --git a/clang/test/SemaTemplate/concepts-GH53354.cpp b/clang/test/SemaTemplate/concepts-GH53354.cpp
new file mode 100644 (file)
index 0000000..4fdf8bd
--- /dev/null
+++ b/clang/test/SemaTemplate/concepts-GH53354.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -std=c++20 -verify %s
+// expected-no-diagnostics
+
+template <template <class> class>
+struct S
+{};
+
+template <class T>
+concept C1 = requires
+{
+  typename S<T::template value_types>;
+};
+
+template <class T>
+requires C1<T>
+struct A {};
+
+template <class T>
+requires C1<T> && true
+struct A<T> {};