https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88869
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Note the auto return type on foo isn't important, it ICEs even with void foo ()
{ C ([] {}); }
The ICE is in
26858 tparms = DECL_TEMPLATE_PARMS (fn_tmpl);
26859 /* If type is a member class template, DECL_TI_ARGS (ctor) will
have
26860 fully specialized args for the enclosing class. Strip those
off, as
26861 the deduction guide won't have those template parameters. */
26862 targs = get_innermost_template_args (DECL_TI_ARGS (ctor),
26863 TMPL_PARMS_DEPTH
(tparms));
because tparms is NULL.
