https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122550
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
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Summary|[14/15/16 Regression] |[14 Regression] constrained
|constrained hidden template |hidden template friend
|friend alongside existing |alongside existing
|declaration is ambiguous |declaration is ambiguous
--- Comment #10 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for 15.3/16 so far.