[Bug c++/106538] New: Reject-valid: Substitution failure causes error with unsatisfied constraint

[dv at vollmann dot ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106538

            Bug ID: 106538
           Summary: Reject-valid: Substitution failure causes error with
                    unsatisfied constraint
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dv at vollmann dot ch
  Target Milestone: ---

Created attachment 53417
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53417&action=edit
Example program that produces the error

If in the attached program ADD_CONSTRAINED_OVERLOAD is defined, the tag_invoke
for connect_t is instantiated.
This instantiation fails for a number of reasons so GCC should continue with
the next overload.  However in this case GCC rejects the code claiming the
contrained is not satisfied (which is correct, but shouldn't cause a reject).