mizvekov added inline comments.
================
Comment at: clang/test/CXX/class/class.compare/class.spaceship/p2.cpp:200
+ struct b3 {
+ auto operator<=>(b3 const &) const = default; // expected-error {{cannot
be deduced because three-way comparison for member 'f' would compare as builtin
type 'void (*)()' which is not currently supported}}
+ // expected-warning@-1 {{implicitly deleted}}
----------------
rsmith wrote:
> I think three-way comparison for function pointers is ill-formed, and that
> the problem in this case is that [over.built] lists candidates for which a
> three-way comparison is invalid. So our overload resolution succeeds, but
> results in a meaningless builtin candidate with an undefined return type.
>
> I think the behavior here after this patch is fine -- we should treat the
> comparison as deleted -- but the diagnostic is wrong. This isn't a "not
> currently supported" case, this is a "not a valid expression" case, per
> [class.compare.default]/3.2 (except that the wording currently gets this
> wrong and doesn't actually say what happens here, because we're actually in
> [class.compare.default]/3.1). Though perhaps the better fix would be to not
> even include a builtin candidate for `operator<=>(void (*)(), void (*)())`?
Yeah this was part of my plan to give the correct diagnostic for function
pointers in the next patch in the series:
https://reviews.llvm.org/D103855
The idea on this one is to produce an error, is the TU will not compile, for
built-in types not supported.
After the next one, we just implicitly delete the comparison for function
pointers, and leave the error for other unimplemented built-in types.
I think this makes more sense, even if we manage to implement this deduction
for all built-in types currently available, it would still be too easy for
another patch to introduce a new built-in types and forget to support it here.
And it does make sense to error on these cases than to simply pick an arbitrary
answer and churn along, I think
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D103850/new/
https://reviews.llvm.org/D103850
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