[Bug c++/113405] Can't access member type alias of concept-constrained class template specialization in global module fragment via alias template in different module

["nathanieloshead at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113405

Nathaniel Shead <nathanieloshead at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |nathanieloshead at gmail dot com

--- Comment #4 from Nathaniel Shead <nathanieloshead at gmail dot com> ---
The issue seems to be that 'depset::hash::add_specializations' only adds the
first of a set of constrained specialisations that use the same arguments. This
comes down to the fact that the 'type_specializations' hashset is only hashed
on the base template and the provided arguments: differently constrained
specialisations just aren't added.

Other parts of the dependency walker seem to handle this OK, by walking the
DECL_TEMPLATE_SPECIALIZATIONS list, but not the base 'specialization_add'
function.

I'm not entirely sure yet what the best way to approach solving this is.