https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101783
Bug ID: 101783
Summary: unnecessary error when top level cv qualifier is
dropped
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nickhuang99 at hotmail dot com
Target Milestone: ---
Created attachment 51261
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51261&action=edit
When no template specialization is at present, static_assert shows correct
function signature. It would impress user this error unnecessary.
The following code:
template<class T> struct A{
typedef T& Type; // #0
};
template<class T> void f(const typename A<T>::Type){} // #1
template <> void f<int>(const typename A<int>::Type){} // #2
will generate error:
error: ‘const’ qualifiers cannot be applied to ‘A<int>::Type’ {aka ‘int&’}
1. This error is unnecessary because the *const* as top level cv qualifier will
be dropped anyway. Considering following correct static assert even without
template specialization of #2 at presence:
static_assert(std::is_same<decltype(f<int>),void(int&)>::value);
The signature of *f<int>* would drop unnecessary const anyway as top-level cv
qualifier according to spec. So, there is no need to generate error.
2. clang gives a warning but still accept it of which I believe appropriate
(https://www.godbolt.org/z/9qWrj5asq). MSVC accept without complaining
(https://www.godbolt.org/z/3coqMnjjq).
3. I have a simple fix for this. By using *tf_keep_type_decl*, it will suppress
this unnecessary error emit and let returning result being validated anyway. In
other words, suppressing this early error doesn't break anything.
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -4104,7 +4104,7 @@ cp_parser_make_typename_type (cp_parser *parser, tree id,
if (identifier_p (id))
{
result = make_typename_type (parser->scope, id, typename_type,
- /*complain=*/tf_none);
+ /*complain=*/tf_keep_type_decl);
if (result == error_mark_node)
cp_parser_diagnose_invalid_type_name (parser, id, id_location);
return result;
