[Clang][Sema] Convert warning for extraneous template parameter lists to an extension warning

[sdkrystian]

We currently accept the following explicit specialization with a warning for the extraneous template parameter list:

template<typename T>
void f();

template<>
template<>
void f<int>(); // warning: extraneous template parameter list in template specialization

This should really be an extension warning so we reject with -pedantic-errors. This patch converts the warning to an extension warning.

(Note: This still needs a release note & a few new tests... I'll be taking care of that tomorrow)

[llvmbot]

@llvm/pr-subscribers-clang

Author: Krystian Stasiowski (sdkrystian)

Changes

We currently accept the following explicit specialization with a warning for the extraneous template parameter list:

template<typename T>
void f();

template<>
template<>
void f<int>(); // warning: extraneous template parameter list in template specialization

This should really be an extension warning so we reject with -pedantic-errors. This patch converts the warning to an extension warning.

---

Full diff: https://github.com/llvm/llvm-project/pull/82277.diff

5 Files Affected:

• (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+1-1)
• (modified) clang/lib/Sema/SemaTemplate.cpp (+1-1)
• (modified) clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p23.cpp (+2-4)
• (modified) clang/test/CXX/drs/dr5xx.cpp (+4-6)
• (modified) clang/test/Misc/warning-flags.c (+1-1)

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index b4dc4feee8e63a..1a7b91bb4b45b6 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5323,7 +5323,7 @@ def err_alias_template_extra_headers : Error<
 def err_template_spec_extra_headers : Error<
   "extraneous template parameter list in template specialization or "
   "out-of-line template definition">;
-def warn_template_spec_extra_headers : Warning<
+def ext_template_spec_extra_headers : ExtWarn<
   "extraneous template parameter list in template specialization">;
 def note_explicit_template_spec_does_not_need_header : Note<
   "'template<>' header not required for explicitly-specialized class %0 "
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index cf781e0e1bf3f4..73c0167ab75778 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -3667,7 +3667,7 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
 
     if (!SuppressDiagnostic)
       Diag(ParamLists[ParamIdx]->getTemplateLoc(),
-           AllExplicitSpecHeaders ? diag::warn_template_spec_extra_headers
+           AllExplicitSpecHeaders ? diag::ext_template_spec_extra_headers
                                   : diag::err_template_spec_extra_headers)
           << SourceRange(ParamLists[ParamIdx]->getTemplateLoc(),
                          ParamLists[ParamLists.size() - 2]->getRAngleLoc());
diff --git a/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p23.cpp b/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p23.cpp
index 469c4e091953c3..683392c5891538 100644
--- a/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p23.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p23.cpp
@@ -1,7 +1,6 @@
 // RUN: %clang_cc1 -std=c++20 -pedantic-errors -verify %s
 
-// FIXME: This should be an error with -pedantic-errors.
-template<> // expected-warning {{extraneous template parameter list in template specialization}}
+template<> // expected-error {{extraneous template parameter list in template specialization}}
 void f(auto);
 
 template<typename>
@@ -18,7 +17,6 @@ void A<T>::g(auto) { }
 template<>
 void A<int>::g(auto) { }
 
-// FIXME: This should be an error with -pedantic-errors.
 template<>
-template<> // expected-warning {{extraneous template parameter list in template specialization}}
+template<> // expected-error {{extraneous template parameter list in template specialization}}
 void A<long>::g(auto) { }
diff --git a/clang/test/CXX/drs/dr5xx.cpp b/clang/test/CXX/drs/dr5xx.cpp
index 21a6646d4abcf1..0e1de342f6706f 100644
--- a/clang/test/CXX/drs/dr5xx.cpp
+++ b/clang/test/CXX/drs/dr5xx.cpp
@@ -354,17 +354,15 @@ namespace dr531 { // dr531: partial
 
     template<> void A<char>::f(char) {}
     // expected-error@-1 {{no function template matches function template specialization 'f'}}
-    // FIXME: This is ill-formed; -pedantic-errors should reject.
     template<> template<typename U> void A<char>::g(char, U) {}
-    // expected-warning@-1 {{extraneous template parameter list in template specialization}}
+    // expected-error@-1 {{extraneous template parameter list in template specialization}}
     //   expected-note@#dr531-A-char {{'template<>' header not required for explicitly-specialized class 'dr531::bad::A<char>' declared here}}
     template<> struct A<char>::B {};
     // expected-error@-1 {{extraneous 'template<>' in declaration of struct 'B'}}
     // expected-error@-2 {{specialization of member 'dr531::bad::A<char>::B' does not specialize an instantiated member}}
     //  expected-note@#dr531-B {{attempt to specialize declaration here}}
-    // FIXME: This is ill-formed; -pedantic-errors should reject.
     template<> template<typename U> struct A<char>::C {};
-    // expected-warning@-1 {{extraneous template parameter list in template specialization}}
+    // expected-error@-1 {{extraneous template parameter list in template specialization}}
     //   expected-note@#dr531-A-char {{'template<>' header not required for explicitly-specialized class 'dr531::bad::A<char>' declared here}}
     template<> char A<char>::n = 0;
     // expected-error@-1 {{extraneous 'template<>' in declaration of variable 'n'}}
@@ -808,7 +806,7 @@ namespace dr571 { // dr571 unknown
   int n;
   // FIXME: Test if this has internal linkage.
   const ir r = n;
-  // expected-warning@-1 {{'const' qualifier on reference type 'ir' (aka 'int &') has no effect}} 
+  // expected-warning@-1 {{'const' qualifier on reference type 'ir' (aka 'int &') has no effect}}
 }
 
 namespace dr572 { // dr572: yes
@@ -990,7 +988,7 @@ namespace dr580 { // dr580: partial
       // FIXME: We incorrectly accept this
       // because we think C2::Y::A<...> might
       // instantiate to C2::X::A
-      template<X::I> struct A {}; 
+      template<X::I> struct A {};
     };
   };
 
diff --git a/clang/test/Misc/warning-flags.c b/clang/test/Misc/warning-flags.c
index 07a75046d4e01b..9d4cac9e39b420 100644
--- a/clang/test/Misc/warning-flags.c
+++ b/clang/test/Misc/warning-flags.c
@@ -26,6 +26,7 @@ CHECK-NEXT:   ext_missing_whitespace_after_macro_name
 CHECK-NEXT:   ext_new_paren_array_nonconst
 CHECK-NEXT:   ext_plain_complex
 CHECK-NEXT:   ext_template_arg_extra_parens
+CHECK-NEXT:   ext_template_spec_extra_headers
 CHECK-NEXT:   ext_typecheck_cond_incompatible_operands
 CHECK-NEXT:   ext_typecheck_ordered_comparison_of_pointer_integer
 CHECK-NEXT:   ext_using_undefined_std
@@ -78,7 +79,6 @@ CHECK-NEXT:   warn_register_objc_catch_parm
 CHECK-NEXT:   warn_related_result_type_compatibility_class
 CHECK-NEXT:   warn_related_result_type_compatibility_protocol
 CHECK-NEXT:   warn_template_export_unsupported
-CHECK-NEXT:   warn_template_spec_extra_headers
 CHECK-NEXT:   warn_tentative_incomplete_array
 CHECK-NEXT:   warn_typecheck_function_qualifiers
 CHECK-NEXT:   warn_undef_interface