cor3ntin added inline comments.
================
Comment at: clang/test/SemaCXX/overloaded-operator-decl.cpp:64
+class E {};
+void operator+(E, ...) {} // expected-error{{overloaded 'operator+' cannot be
variadic}}
+void d() { E() + E(); }
----------------
aaron.ballman wrote:
> Fznamznon wrote:
> > aaron.ballman wrote:
> > > I think it might make sense to extend the test coverage for the other
> > > operators you can overload, just to demonstrate we diagnose them all
> > > consistently. WDYT?
> > Okay, while trying to add more test cases I discovered that following
> > ```
> > class E {};
> > bool operator<(const E& lhs, ...);
> > auto operator<=>(const E& lhs, ...);
> >
> > void d() {
> > E() < E();
> > }
> > ```
> > crashes even with the patch since there is code searching for best overload
> > candidate that doesn't consider possibility for them making variadic.
> > The code around overloading is actually pretty inconsistent, somewhere
> > invalid candidates are considered, and somewhere not, so I spent some time
> > not knowing what to do.
> > I'm now inclined that we just shouldn't consider invalid candidates like
> > @shafik
> > suggests. WDYY?
> >
> Overload resolution doesn't need to produce a candidate that's viable to
> call; C++ lets you resolve to the "best viable function" only to say "and
> that one wasn't good enough either." e.g.,
> http://eel.is/c++draft/over#match.general-3
>
> I've not yet spotted anything in http://eel.is/c++draft/over that says
> invalid declarations should/should not be added to the initial candidate set.
> I *think* the intention is that if name lookup can find the name, it goes
> into the candidate set. Then that set is processed to remove functions that
> are not viable (http://eel.is/c++draft/over.match.viable). Then we find the
> best viable function from that set.
>
> I think we should be keeping the function in the candidate set so long as it
> matches the rules in http://eel.is/c++draft/over.match.viable even if the
> function is otherwise not viable. Otherwise, correcting an unrelated issue
> might change overload resolution to find a completely different function.
> e.g., in my example above, we'd select `void overloaded(int);` as the best
> viable function, but when the user corrects the `float` function, we'd change
> to call that instead. I think it's easier to understand what's going on when
> picking the `float` overload to begin with and saying "but we can't call that
> because it's busted".
>
> CC @cor3ntin @hubert.reinterpretcast @rsmith for some extra opinions, as I'm
> not certain if I'm interpreting the standard correctly or not.
I'm not sure how much the standardese matter here as the declaration of the
operators are ill-formed anyway.
But from a QOI perspective, i think keeping in the set everything the users
might reasonably expect to be considered makes sense to me, as it *should* lead
to better diagnostics
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D156244/new/
https://reviews.llvm.org/D156244
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