https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99963
Bug ID: 99963
Summary: [concepts] template <concept> vs concept auto reports
ambiguous overload
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ldalessandro at gmail dot com
Target Milestone: ---
Consider the following code (https://godbolt.org/z/h1bz1qxan).
#include <concepts>
struct A{};
struct B : A {};
template <class T>
concept is_a = std::is_base_of_v<A, T>;
template <class T>
concept is_b = is_a<T> and std::same_as<B, T>;
int foo(is_a auto, is_a auto);
#ifdef OK
int foo(is_b auto, is_a auto);
#else
template <is_a A>
int foo(is_b auto, A);
#endif
A a;
B b;
int d = foo(b, a);
<source>:23:12: error: call of overloaded 'foo(B&, A&)' is ambiguous
23 | int d = foo(b, a);
| ~~~^~~~~~
With -DOK, which enables is_a auto syntax, this compiles. The template <is_a>
fails.
