[Bug c++/67969] [concepts] bug with overloaded function when using constraints

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67969

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |7.0
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Amir Kirsh from comment #4)
> // Bug still exists in gcc 11.2 
> 
> template<typename T>
> concept SmallVar = (sizeof(T) <= sizeof(int));
> 
> void print(SmallVar auto t) {
>     std::cout << t << std::endl;
> }
> 
> void print(const auto& t) {
>     std::cout << t << std::endl;
> }
> 
> int main() {
>     static_assert(SmallVar<int>); // ok
>     static_assert(SmallVar<decltype(6)>); // ok
>     static_assert(!SmallVar<long long>); // ok
>     print("hello");
>     print('a'); // gcc 11.2 sees here ambiguity
>     print(6);  // gcc 11.2 sees here ambiguity
> }
> 
> Code:
> https://godbolt.org/z/jq8edKM3E

I think GCC is correct to reject those calls as ambiguous because during
partial ordering of two function templates, their constraints are considered
only if the two templates have equivalent function parameter types
(wg21.link/temp.func.order#6.2.2).  So both 'print' templates need to declare
't' consistently, e.g. https://godbolt.org/z/MMY351T9M, before constraint
subsumption can kick in as a tiebreaker.

Looks like the comment #1 testcase was fixed with r7-1159, so resolving as
fixed.