https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82833
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Looks like the ICE was fixed by the concepts rewrite in r10-3735 "Update the
concepts implementation to conform to C++20."
Valid C++20 testcase:
#include <functional>
#include <concepts>
template <typename T, auto A, typename M>
concept CallYieldsType = requires(T t) {
{ std::invoke(A, t) } -> std::same_as<M>;
};
template <typename T>
struct S {
struct Z;
template <auto A>
requires CallYieldsType<T, A, Z>
struct N;
};
template <typename T>
template <auto A>
requires CallYieldsType<T, A, typename S<T>::Z>
struct S<T>::N {
Z &f(T t) {
return std::invoke(A, t);
}
};
Bisections shows this started to be accepted with r11-3713:
c++: Set the constraints of a class type sooner [PR96229]
In the testcase below, during processing (at parse time) of Y's base
class X<Y>, convert_template_argument calls is_compatible_template_arg
to check if the template argument Y is no more constrained than the
parameter P. But at this point we haven't yet set Y's constraints, so
get_normalized_constraints_from_decl yields NULL_TREE as the normal form
and caches this result into the normalized_map.
We set Y's constraints later in cp_parser_class_specifier_1 but the
stale normal form in the normalized_map remains. This ultimately causes
us to miss the constraint failure for Y<Z> because according to the
cached normal form, Y is not constrained.
This patch fixes this issue by moving up the call to
associate_classtype_constraints so that we set constraints before we
start processing a class's bases.
gcc/cp/ChangeLog:
PR c++/96229
* parser.c (cp_parser_class_specifier_1): Move call to
associate_classtype_constraints from here to ...
(cp_parser_class_head): ... here.
* pt.c (is_compatible_template_arg): Correct documentation to
say "argument is _no_ more constrained than the parameter".
gcc/testsuite/ChangeLog:
PR c++/96229
* g++.dg/cpp2a/concepts-class2.C: New test.
