[Bug libstdc++/100667] [11/12/13/14 Regression] std::tuple cannot be constructed from A&&, if A not defined (only forward declared)

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100667

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oh interestingly __is_constructible(Incomplete&&, Incomplete) is already
allowed, but __is_nothrow_constructible and __is_convertible give errors:


__is_nothrow_constructible(Incomplete&&, Incomplete)

<stdin>: In function ‘int main()’:
<stdin>:117:68: error: invalid use of incomplete type ‘struct Incomplete’
[-fpermissive]
<stdin>:110:8: note: forward declaration of ‘struct Incomplete’

__is_convertible(Incomplete, Incomplete&&)

<stdin>: In function ‘int main()’:
<stdin>:117:58: error: invalid use of incomplete type ‘struct Incomplete’
[-fpermissive]
<stdin>:110:8: note: forward declaration of ‘struct Incomplete’