[C++20] [Modules] Profile TemplateName by canonical decl

Close llvm/llvm-project#61317

The root cause of the problem is that we profile TemplateName by the
non-canonical decls so that the compiler thought they are two different
types. But this is not true. We fixed the issue after we profile the
template name by using the same name.

clang/include/clang/AST/TemplateName.h

@@ -351,9 +351,7 @@ class TemplateName {
   /// error.
   void dump() const;
 
-  void Profile(llvm::FoldingSetNodeID &ID) {
-    ID.AddPointer(Storage.getOpaqueValue());
-  }
+  void Profile(llvm::FoldingSetNodeID &ID);
 
   /// Retrieve the template name as a void pointer.
   void *getAsVoidPointer() const { return Storage.getOpaqueValue(); }

clang/lib/AST/TemplateName.cpp

@@ -281,6 +281,13 @@ bool TemplateName::containsUnexpandedParameterPack() const {
   return getDependence() & TemplateNameDependence::UnexpandedPack;
 }
 
+void TemplateName::Profile(llvm::FoldingSetNodeID &ID) {
+  if (auto *TD = getAsTemplateDecl())
+    ID.AddPointer(TD->getCanonicalDecl());
+  else
+    ID.AddPointer(Storage.getOpaqueValue());
+}
+
 void TemplateName::print(raw_ostream &OS, const PrintingPolicy &Policy,
                          Qualified Qual) const {
   auto Kind = getKind();

clang/test/Modules/pr61317.cppm

@@ -0,0 +1,49 @@
+// From https://github.com/llvm/llvm-project/issues/61317
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/A.cppm -emit-module-interface -o %t/A.pcm
+// RUN: %clang_cc1 -std=c++20 %t/B.cppm -emit-module-interface -o %t/B.pcm \
+// RUN:     -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/Use.cpp -fprebuilt-module-path=%t -fsyntax-only -verify
+
+//--- foo.h
+#ifndef _FOO
+#define _FOO
+
+template <typename T> struct Foo {
+  Foo(T) {}
+};
+
+template <typename T> Foo(T&) -> Foo<T>;
+
+struct Bar {
+  template <typename T>
+    requires requires { Foo{T()}; }
+  void baz() const {}
+};
+
+#endif
+
+//--- A.cppm
+module;
+#include "foo.h"
+export module A;
+export using ::Foo;
+export using ::Bar;
+
+//--- B.cppm
+module;
+#include "foo.h"
+export module B;
+export import A;
+
+//--- Use.cpp
+// expected-no-diagnostics
+import A;
+import B;
+void use() {
+  Bar _; 
+  _.baz<int>();
+}