[Bug c++/113064] assignement from temporary sometimes invokes copy-assign instead of move-assign operator

[mpolacek at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113064

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to m.cencora from comment #4)
> This also might be a just another symptom of the same root cause:
> 
> struct bar
> {
>     bar() = default;
> 
>     bar(const bar&);
>     bar(bar&&);
> 
>     bar& operator=(const bar&);
>     bar& operator=(bar&&);
> };
> 
> struct foo
> {
>     operator const bar& () const &;
> 
>     operator bar& () &;
> 
>     operator bar&&() &&;
> };
> 
> void test()
> {
>     bar a = foo{}; // ok
> 
>     a = foo{}; // not ok - ambiguous call, but why? &&-qualified looks like
> a better match
> 
>     foo f;
>     a = f; // ok
> 
>     a = static_cast<const foo&>(foo{}); // ok
> }

Here the error showed up in r9-6486:

commit c7e936dbc7f59ad09c28ef57e5399a4256061747
Author: Jason Merrill <ja...@redhat.com>
Date:   Mon Mar 11 23:19:22 2019 -0400

    PR c++/86521 - wrong overload resolution with ref-qualifiers.

    Here we were wrongly treating binding a const lvalue ref to an xvalue as
    direct binding, which is wrong under [dcl.init.ref] and [over.match.ref].