[Bug c++/69701] "v.operator T()" incorrectly parsed if "v.T()" present.

[Bug c++/69701] "v.operator T()" incorrectly parsed if "v.T()" present.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69701

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
ICC also rejects this for the same reason as GCC while both MSVC and clang
accept it.  Maybe there is a defect report about this.

[Bug c++/69701] "v.operator T()" incorrectly parsed if "v.T()" present.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69701

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-12-03
           Keywords|                            |accepts-invalid
             Status|UNCONFIRMED                 |NEW

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Here is a different testcase which shows we also have an accepts invalid:
class A {};
class B {
  typedef int AT;
public:
 operator AT () const noexcept { return {}; }
 typedef int A;
};
int main() {
  B b;
  b.operator A();
}

I have not looked up in the standard which A is supposed to be found here (for
b.operator A) is it B::A or ::A?

[Bug c++/69701] "v.operator T()" incorrectly parsed if "v.T()" present.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69701

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|accepts-invalid             |

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So I think clang and MSVC have a bug in this area too.

See basic.lookup.classref/7 :
If the id-expression is a conversion-function-id, its conversion-type-id is
first looked up in the class of the object
expression (11.8) and the name, if found, is used. Otherwise it is looked up in
the context of the entire
postfix-expression. In each of these lookups, only names that denote types or
templates whose specializations
are types are considered. [Example:
struct A { };
namespace N {
struct A {
void g() { }
template <class T> operator T();
};
}
int main() {
N::A a;
a.operator A(); // calls N::A::operator N::A
}
— end example]

If we take the example, clang and MSVC calls N::A::operator ::A and not what
the standard says.

GCC I think is still wrong in the original testcase I think because B::A does
not represent a type .
In my example in comment #4, GCC and ICC does the correct thing and selects the
correct type.

[Bug c++/69701] "v.operator T()" incorrectly parsed if "v.T()" present.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69701

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1291

[Accepted at the November, 2020 meeting as part of paper P1787R6 and moved to
DR at the February, 2021 meeting.]




So there is a defect report in this area after all ....

[Bug c++/69701] "v.operator T()" incorrectly parsed if "v.T()" present.

[language.lawyer at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69701

Language Lawyer <language.lawyer at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |language.lawyer at gmail dot com

--- Comment #7 from Language Lawyer <language.lawyer at gmail dot com> ---
Another example related to CWG2396:

struct B
{
    struct S {};
    operator S();
}; 

auto v = B{}.operator struct S(); // error: 'struct B' has no member named
'operator S'

It can be checked that GCC injects unrelated `struct S` into the global
namespace and then tries to find `operator struct ::S` in B.

However, according to P1787R6 [basic.lookup.unqual]/5: An unqualified name that
is a component name of a type-specifier or ptr-operator of a conversion-type-id
is looked up in the same fashion as the conversion-function-id in which it
appears.

In an elaborated-type-specifier of the form "class-key identifier", such as
`struct S`, identifier is a component name ([dcl.type.elab]/1), so S shall be
searched in B first.