[Bug c++/54309] New: type alias accessing class template enum type member fails

[Bug c++/54309] New: type alias accessing class template enum type member fails

[paul at preney dot ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54309

             Bug #: 54309
           Summary: type alias accessing class template enum type member
                    fails
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: paul@preney.ca


Created attachment 28046
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28046
Source code demonstrating the bug.

This is easier to see not working than to describe. The code that does not work
(i.e., "not ok: BUG" comment in the example) works if you replace the using
type alias with a typedef instead though (which means that is a work-around for
now).

This bug was tested with these versions of GCC:

  g++ v4.7.0
  g++ v4.8.0 (snapshot 20120812)

The error message (from GCC v4.8):

$ g++-4.8.0-alpha20120812 -std=c++11 gcc-cxx-bug.cxx 
gcc-cxx-bug.cxx: In instantiation of ‘void func() [with T = int]’:
gcc-cxx-bug.cxx:25:13:   required from here
gcc-cxx-bug.cxx:15:24: error: no type named ‘Stuff’ in ‘using test = class
Foo<T>’
   typename test::Stuff b = test::Stuff::beta; // not ok: BUG
                        ^
gcc-cxx-bug.cxx:15:24: error: no type named ‘Stuff’ in ‘using test = class
Foo<T>’
gcc-cxx-bug.cxx:15:24: error: no type named ‘Stuff’ in ‘using test = class
Foo<T>’
$

(I also tried this code with clang++ (v3.1) and it compiles successfully as
expected.)


It appears to only occur when a using type alias (i.e., the "test" alias in the
example) is used to access a template class' member that is an enum type (i.e.,
"Foo<T>::Stuff" in the example) when the class template parameter is not
hard-coded using the using type alias (i.e., Foo<T> is used but Foo<int> is
okay). The code triggering the issue follows and is attached.


template <typename T>
class Foo
{
  public:
    enum class Stuff { alpha, beta };
};

template <typename T>
void func()
{
  typename Foo<T>::Stuff a = Foo<T>::Stuff::alpha; // ok
  a = a;

  using test = Foo<T>;
  typename test::Stuff b = test::Stuff::beta; // not ok: BUG
  b = b;

  typedef Foo<T> test2;
  typename test2::Stuff c = test2::Stuff::beta; // ok
  c = c;
}

int main()
{
  func<int>();

  {
    Foo<int>::Stuff a = Foo<int>::Stuff::alpha; // ok
    a = a;

    using test = Foo<int>;
    typename test::Stuff b = test::Stuff::beta; // ok
    b = b;

    typedef Foo<int> test2;
    typename test2::Stuff c = test2::Stuff::beta; // ok
    c = c;
  }
}

[Bug c++/54309] [C++11] type alias accessing class template enum type member fails

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54309

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |rejects-valid
   Last reconfirmed|                            |2012-08-18
     Ever Confirmed|0                           |1
            Summary|type alias accessing class  |[C++11] type alias
                   |template enum type member   |accessing class template
                   |fails                       |enum type member fails
           Severity|major                       |normal

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-08-18 06:02:03 UTC ---
It looks like the using alias is not setup to late bind.

[Bug c++/54309] [C++11] type alias accessing class template typename

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54309

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[C++11] type alias          |[C++11] type alias
                   |accessing class template    |accessing class template
                   |enum type member fails      |typename

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-08-18 06:05:37 UTC ---
Also enum is not the only issue, it is an issue with any subnames of the type
alias.
template <typename T>
struct Foo
{
    typedef int Stuff;
};

template <typename T>
void func()
{
  typename Foo<T>::Stuff a = 1;
  a = a;

  using test = Foo<T>;
  typename test::Stuff b;
  b = b;

  typedef Foo<T> test2;
  typename test2::Stuff c = 2;
  c = c;
}

int main()
{
  func<int>();

  {
    Foo<int>::Stuff a = 1;
    a = a;

    using test = Foo<int>;
    typename test::Stuff b = 2;
    b = b;

    typedef Foo<int> test2;
    typename test2::Stuff c = 3;
    c = c;
  }
}

[Bug c++/54309] [C++11] type alias accessing class template typename

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54309

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dodji at gcc dot gnu.org

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-08-18 09:40:35 UTC ---
Maybe Dodji is willing to have a look to this one too.

[Bug c++/54309] [C++11] type alias accessing class template typename

[dodji at seketeli dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54309

--- Comment #4 from dodji at seketeli dot org <dodji at seketeli dot org> 2012-08-20 12:10:27 UTC ---
I think this is the same problem as PR c++/53540 for which a candidate
patch was sent to the gcc-patches mailing list [1].

So unless I am mistaken, I am marking this bug as a duplicate of the
former.

[1]: http://gcc.gnu.org/ml/gcc-patches/2012-08/msg01111.html

[Bug c++/54309] [C++11] type alias accessing class template typename

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54309

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-08-20 12:12:44 UTC ---
Ah great, I suspected that.

[Bug c++/54309] [C++11] type alias accessing class template typename

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54309

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
      Known to work|                            |4.8.0, 4.9.0
         Resolution|                            |DUPLICATE

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-05-03 09:54:21 UTC ---
Thus this works in the released 4.8.0.

*** This bug has been marked as a duplicate of bug 53540 ***