[Bug c++/99678] New: c++20 trailing requires clauses allows undeclared identifier

[Bug c++/99678] New: c++20 trailing requires clauses allows undeclared identifier

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

            Bug ID: 99678
           Summary: c++20 trailing requires clauses allows undeclared
                    identifier
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

https://godbolt.org/z/reG8qE

====

void bar(auto) requires undeclared_identifier;

====

GCC accepts this code.

[Bug c++/99678] c++20 trailing requires clauses allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nshead at gcc dot gnu.org

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 114946 has been marked as a duplicate of this bug. ***

[Bug c++/99678] [concepts] requires-clause allows undeclared identifier

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99678

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|c++20 trailing requires     |[concepts] requires-clause
                   |clauses allows undeclared   |allows undeclared
                   |identifier                  |identifier
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
From PR114946:

(In reply to Nathaniel Shead from comment #0)
> The following sample compiles fine with 'g++ -std=c++20 -pedantic-errors':
> 
>   template <typename T>
>     requires xxxx
>   struct S {};
> 
>   template <typename T>
>     requires xxxx
>   void foo() {}
> 
> Note that 'xxxx' has not been declared or defined.  Both MSVC and Clang
> complain about the undeclared identifier.  GCC does error if we attempt to
> instantiate either of these specialisations, but they always (silently) lose
> to a better match:
> 
>   template <typename T> struct S {};
>   template <typename T> requires xxxx struct S<T> {};
> 
>   template <typename T> void foo() {}
>   template <typename T> requires xxxx void foo() {}
> 
>   int main() {
>     S<int> x;
>     foo<int>();
>   }