[Bug c++/92268] Constraint normalization substitutes parameter too early
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92268
Jason Merrill changed:
What|Removed |Added
CC||jason at gcc dot gnu.org
--- Comment #4 from Jason Merrill ---
Smaller example:
template concept Two = true;
template concept One = Two;
template concept Zero = requires
{
{ T() } -> One;
};
template
void f() requires Zero;
template
void f(...);
int main()
{
f();
}
[Bug c++/92268] Constraint normalization substitutes parameter too early
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92268 Andrew Sutton changed: What|Removed |Added CC||andrew.n.sutton at gmail dot com --- Comment #3 from Andrew Sutton --- > [02:40] but it looks like when we normalize the forward_iterator > constraint on the compound-requirement we're normalizing > forward_iterator, which is wrong -- we should be normalizing > forward_iterator, and then checking whether that's satisfied with iterator > [02:40] Andrew sent me a patch to improve handling of nested > requirements that I haven't looked at yet, it may help with this This patch doesn't touch that. We're definitely not normalizing that constraint at the point it appears. It's normalized w.r.t., substituted arguments in do_auto_deduction. I suppose the right thing to do is deduction vs. an unconstrained type, then satisfaction vs. result.
[Bug c++/92268] Constraint normalization substitutes parameter too early
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92268
--- Comment #2 from Jonathan Wakely ---
(Comment 1 was wrong)
A workaround is to replace the compound-requirement with a simple-requirement
that depends on a function constrained with the desired constraint:
template void workaround(I) { }
template
concept F = requires (T& t) { workaround(t.begin()); };
[Bug c++/92268] Constraint normalization substitutes parameter too early
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92268
--- Comment #1 from Jonathan Wakely ---
The workaround is to require that the common_reference_t types exist:
template
concept common_reference_with
=
//
requires { typename common_reference_t;
typename common_reference_t; }
&&
//
foo, common_reference_t>
&& bar, common_reference_t>
&& baz, common_reference_t>;
[Bug c++/92268] Constraint normalization substitutes parameter too early
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92268 Jonathan Wakely changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2019-10-29 Ever confirmed|0 |1
