[Bug c++/90936] New: [9 Regression] Ambiguous call with ref-qualified conversion operators

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90936

            Bug ID: 90936
           Summary: [9 Regression] Ambiguous call with ref-qualified
                    conversion operators
           Product: gcc
           Version: 9.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: m.cencora at gmail dot com
  Target Milestone: ---

gcc 9 and trunk complains about ambiguous call when constructing or assigning
to f2.
This works fine with gcc 8 or earlier.

struct Foo
{};

struct ConvertibleToFoo
{
    operator const Foo&() const &;

    operator Foo&&() &&;
};

void bar()
{
    Foo f1(static_cast<const ConvertibleToFoo&>(ConvertibleToFoo{}));
    Foo f2(static_cast<ConvertibleToFoo&&>(ConvertibleToFoo{}));
    f1 = static_cast<const ConvertibleToFoo&>(ConvertibleToFoo{});
    f2 = static_cast<ConvertibleToFoo&&>(ConvertibleToFoo{});
}