https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93154
--- Comment #2 from DB <db0451 at gmail dot com> ---
A reduced version, without a variadic pack of functions...
```
#include <concepts>
void f1(int) {}
template <typename F>
auto
make_lambda(F f)
{
return [f] <typename Arg>
requires std::invocable<F, Arg>
(Arg a)
{
f(a);
};
}
auto
main() -> int
{
auto const lambda = make_lambda(&f1);
lambda(42);
return 0;
}
```
...gives an error that is now specific, but which still seems clearly wrong:
>>>
test5.cpp: In function ‘int main()’:
test5.cpp:19:11: error: no match for call to ‘(const make_lambda(F) [with F =
void (*)(int)]::<lambda(Arg)>) (int)’
19 | lambda(42);
| ^
test5.cpp:9:9: note: candidate: ‘make_lambda(F) [with F = void
(*)(int)]::<lambda(Arg)> [with Arg = int]’
9 | return [f] <typename Arg> requires std::invocable<F, Arg> (Arg a)
| ^
test5.cpp:9:9: note: constraints not satisfied
In file included from test5.cpp:1:
/usr/include/c++/10/concepts: In instantiation of ‘make_lambda(F) [with F =
void (*)(int)]::<lambda(Arg)> [with Arg = int]’:
test5.cpp:19:11: required from here
/usr/include/c++/10/concepts:344:13: required for the satisfaction of
‘invocable<int, Arg>’
/usr/include/c++/10/concepts:344:25: note: the expression ‘is_invocable_v<_Fn,
_Args ...>’ evaluated to ‘false’
344 | concept invocable = is_invocable_v<_Fn, _Args...>;
>>>
It looks like the compiler is mixing up the template arguments of the outer
function and the inner lambda.
In that sense, this might have the same root cause as
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93152
