[clang][Sema] Fix a crash when instantiating a non-type template argument in a dependent scope.

[0x59616e]

Summary

The type alias template is not diagnosed when instantiate an expected non-type template under dependent scope, causing ICE.

Besides that, the diagnostic message has been updated to account for the fact that the function template is not the only non-type template.

Fixes #62533

[0x59616e]

Should I put a description of this fix in ReleaseNote ?

[erichkeane]

Yes, please do add a release note!

[0x59616e]

Add release note.

[erichkeane]

clang/docs/ReleaseNotes.rst

440–441

[0x59616e]

Address feedbacks.

[erichkeane]

LGTM! Feel free to commit

[0x59616e]

Thanks for reviewing ! ;)

clang/docs/ReleaseNotes.rst

 - Fix crash on attempt to initialize union with flexible array member.
   (`#61746 <https://github.com/llvm/llvm-project/issues/61746>`_).
 - Clang `TextNodeDumper` enabled through `-ast-dump` flag no longer evaluates the
   initializer of constexpr `VarDecl` if the declaration has a dependent type.
 - Match GCC's behavior for ``__builtin_object_size`` and
   ``__builtin_dynamic_object_size`` on structs containing flexible array
   members.
   (`#62789 <https://github.com/llvm/llvm-project/issues/62789>`_).
-
+- Fix a crash when instantiating a non-type template argument in a dependent scope.
+  (`#62533 <https://github.com/llvm/llvm-project/issues/62533>`_).
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed a bug where attribute annotations on type specifiers (enums, classes,
   structs, unions, and scoped enums) were not properly ignored, resulting in
   misleading warning messages. Now, such attribute annotations are correctly

clang/include/clang/Basic/DiagnosticSemaKinds.td

 def err_template_kw_refers_to_non_template : Error<
   "%0%select{| following the 'template' keyword}1 "
   "does not refer to a template">;
 def note_template_kw_refers_to_non_template : Note<
   "declared as a non-template here">;
 def err_template_kw_refers_to_dependent_non_template : Error<
   "%0%select{| following the 'template' keyword}1 "
   "cannot refer to a dependent template">;
-def err_template_kw_refers_to_class_template : Error<
-  "'%0%1' instantiated to a class template, not a function template">;
-def note_referenced_class_template : Note<
-  "class template declared here">;
+def err_template_kw_refers_to_type_template : Error<
+  "'%0%1' is expected to be a non-type template, but instantiated to a %select{class|type alias}2 template">;
+def note_referenced_type_template : Note<
+  "%select{class|type alias}0 template declared here">;
 def err_template_kw_missing : Error<
   "missing 'template' keyword prior to dependent template name '%0%1'">;
 def ext_template_outside_of_template : ExtWarn<
   "'template' keyword outside of a template">, InGroup<CXX11>;
 def warn_cxx98_compat_template_outside_of_template : Warning<
   "use of 'template' keyword outside of a template is incompatible with C++98">,
   InGroup<CXX98Compat>, DefaultIgnore;
 

clang/lib/Sema/SemaTemplate.cpp

if (R.isAmbiguous())
     return ExprError();
 
   if (R.empty()) {
     Diag(NameInfo.getLoc(), diag::err_no_member)
       << NameInfo.getName() << DC << SS.getRange();
     return ExprError();
   }
 
-  if (ClassTemplateDecl *Temp = R.getAsSingle<ClassTemplateDecl>()) {
-    Diag(NameInfo.getLoc(), diag::err_template_kw_refers_to_class_template)
-      << SS.getScopeRep()
-      << NameInfo.getName().getAsString() << SS.getRange();
-    Diag(Temp->getLocation(), diag::note_referenced_class_template);
+  auto DiagnoseTypeTemplateDecl = [&](TemplateDecl *Temp,
+                                      bool isTypeAliasTemplateDecl) {
+    Diag(NameInfo.getLoc(), diag::err_template_kw_refers_to_type_template)
+        << SS.getScopeRep() << NameInfo.getName().getAsString() << SS.getRange()
+        << isTypeAliasTemplateDecl;
+    Diag(Temp->getLocation(), diag::note_referenced_type_template) << 0;
     return ExprError();
-  }
+  };
+
+  if (ClassTemplateDecl *Temp = R.getAsSingle<ClassTemplateDecl>())
+    return DiagnoseTypeTemplateDecl(Temp, false);
+
+  if (TypeAliasTemplateDecl *Temp = R.getAsSingle<TypeAliasTemplateDecl>())
+    return DiagnoseTypeTemplateDecl(Temp, true);
 
   return BuildTemplateIdExpr(SS, TemplateKWLoc, R, /*ADL*/ false, TemplateArgs);
 }
 
 /// Form a template name from a name that is syntactically required to name a
 /// template, either due to use of the 'template' keyword or because a name in
 /// this syntactic context is assumed to name a template (C++ [temp.names]p2-4).
 ///

clang/test/SemaCXX/PR62533.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+template<typename T>
+struct test {
+  template<typename> using fun_diff = char; // expected-note 2{{class template declared here}}
+};
+
+template<typename T, typename V>
+decltype(T::template fun_diff<V>) foo1() {}
+// expected-note@-1 {{candidate template ignored: substitution failure [with T = test<int>, V = int]: 'test<int>::fun_diff' is expected to be a non-type template, but instantiated to a type alias template}}
+
+template<typename T>
+void foo2() {
+  // expected-error@+1 {{test<int>::fun_diff' is expected to be a non-type template, but instantiated to a type alias template}}
+  int a = test<T>::template fun_diff<int>;
+}
+
+template<typename T, typename V>
+struct has_fun_diff {
+  using type = double;
+};
+
+template<typename T>
+struct has_fun_diff<T, int> {
+  // expected-error@+1 {{'test<int>::fun_diff' is expected to be a non-type template, but instantiated to a type alias template}}
+  using type = decltype(T::template fun_diff<int>);
+};
+
+void bar() {
+  foo1<test<int>, int>(); // expected-error {{no matching function for call to 'foo1'}}
+  foo2<int>(); // expected-note {{in instantiation of function template specialization}}
+  has_fun_diff<test<int>, int>::type a; // expected-note {{in instantiation of template class}}
+}

clang/test/SemaTemplate/ms-sizeof-missing-typename.cpp

struct Bar {
   struct InnerTemplate { int x[N]; };
   typedef double InnerType;
   static const int InnerVar = 42;
 };
 template struct Foo<Bar>; // expected-note-re {{in instantiation {{.*}} requested here}}
 }
 
 namespace ambiguous_missing_parens {
-// expected-error@+1 {{'Q::U' instantiated to a class template, not a function template}}
+// expected-error@+1 {{'Q::U' is expected to be a non-type template, but instantiated to a class template}}
 template <typename T> void f() { int a = sizeof T::template U<0> + 4; }
 struct Q {
   // expected-note@+1 {{class template declared here}}
   template <int> struct U {};
 };
 // expected-note-re@+1 {{in instantiation {{.*}} requested here}}
 template void f<Q>();
 }