Explicit instantiation of a class with concept'ed methods

[Bonita Montero]

Look at this code:

#include <concepts>

using namespace std;

struct A
{
void op();
};

struct B
{
void op( bool );
};

template<typename T>
concept concept_C = is_same<T, A>::value || is_same<T, B>::value;

template<typename T>
requires concept_C<T>
struct C
{
void opA()
requires is_same<T, A>::value;
void opB( bool f )
requires is_same<T, B>::value;
T *pt;
};

template<typename T>
requires concept_C<T>
void C<T>::opA()
requires is_same<T, A>::value
{
pt->op();
}

template<typename T>
requires concept_C<T>
void C<T>::opB( bool f )
requires is_same<T, B>::value
{
pt->op( f );
}

template
struct C<A>;

template
struct C<B>;

MSVC will instantiate opA for A as well as B and opB
also for A as well as B and gives the following errors:

(42,10): error : too many arguments to function call, expected 0, have 1
(46,8): message : in instantiation of member function 'C<A>::opB'
requested here
(7,7): message : 'op' declared here
(34,9): error : too few arguments to function call, expected 1, have 0
(49,8): message : in instantiation of member function 'C<B>::opA'
requested here
(12,7): message : 'op' declared here

clang gives similar errors, but g++12 is smarter and skips inappropriate
compilation, i.e. filters the functions through their concepts, i.e. it
compiles opA only for A and opB only for B - so which compiler is right
here ? And is there a workaround ?

[Bonita Montero]

I wrote the same thing on Stack Overflow. C<A>::opB( bool )
and C<B>::opA() shouldn't be instantiated according to the
standard. So this is a bug of clang. MSVC has fixed the bug
in the latest release.