https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94894
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|13.0 |---
Status|RESOLVED |NEW
Resolution|FIXED |---
CC| |jason at gcc dot gnu.org
--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Good point, this PR is only partially fixed then (since GCC 13).
Avoiding the unnecessary instantiation in the original example and in your
example seems tricky in general unfortunately. GCC already shortcuts
consideration of template candidates when it sees a perfect non-template
candidate, but in these examples we want to shortcut consideration of other
non-template candidates when we see a perfect non-template candidate. IIUC
such shortcutting would be unsound because if there were multiple perfect
non-template candidates then we would overlook that and fail to diagnose
ambiguity.
(Note that the compiler needs to instantiate restrictive<0> when considering
the 'unrelated' candidate because restrictive<0> might be derived from
'unrelated' (e.g. through a partial specialization), which would make the
candidate viable after all.)
So one workaround that might work for your use case is to turn the problematic
'unrelated' overload into a template, e.g.
template<class...> void fun(unrelated) {}
