https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115656
--- Comment #2 from Sean Murthy <s.murthy at outlook dot com> ---
Compiler version: GCC 11.1 through GCC 14.1
Compiler options: -std=c++20 -Wall -Wextra -pedantic -pedantic-errors
-Werror=pedantic
Compiler output:
<source>: In function 'int main()':
<source>:39:13: error: class template argument deduction failed:
39 | A a2(45l); //Error GCC 11.1+: uncomment line above, the error
disappears
| ^
<source>:39:13: error: no matching function for call to 'A(long int)'
<source>:20:5: note: candidate: 'template<class U, template<class> class
requires unsigned_integral< <template-parameter-2-1> > V, class S> requires
signed_integral<S> A(S)-> A<U, V>'
20 | A(S s) : u_( s < 0 ? -s : s) {}
| ^
<source>:20:5: note: template argument deduction/substitution failed:
<source>: In substitution of 'template<class U, template<class> class requires
unsigned_integral< <template-parameter-2-1> > V, class S> requires
signed_integral<S> A(S)-> A<U, V> [with U = unsigned int; V = dv; S = long
int]':
<source>:39:13: required from here
39 | A a2(45l); //Error GCC 11.1+: uncomment line above, the error
disappears
| ^
<source>:20:5: error: template constraint failure for 'template<class U,
template<class> class requires unsigned_integral< <template-parameter-2-1> >
V> requires unsigned_integral<U> struct A'
20 | A(S s) : u_( s < 0 ? -s : s) {}
| ^
<source>:20:5: note: constraints not satisfied
<source>:17:5: note: candidate: 'template<class U, template<class> class
requires unsigned_integral< <template-parameter-2-1> > V> A(U)-> A<U, V>'
17 | A(U u) : u_(u) {};
| ^
<source>:17:5: note: template argument deduction/substitution failed:
<source>:13:8: note: candidate: 'template<class U, template<class> class
requires unsigned_integral< <template-parameter-2-1> > V> A(A<U, V>)-> A<U,
V>'
13 | struct A
| ^
<source>:13:8: note: template argument deduction/substitution failed:
<source>:39:13: note: mismatched types 'A<U, V>' and 'long int'
39 | A a2(45l); //Error GCC 11.1+: uncomment line above, the error
disappears
| ^
