aaron.ballman added subscribers: cor3ntin, hubert.reinterpretcast, rsmith.
aaron.ballman 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(); }
----------------
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.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D156244/new/
https://reviews.llvm.org/D156244
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