[Bug c++/56886] New: [4.9 regression] undesirable instantiation of class template default argument

[Bug c++/56886] New: [4.9 regression] undesirable instantiation of class template default argument

[zeratul976 at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56886

             Bug #: 56886
           Summary: [4.9 regression] undesirable instantiation of class
                    template default argument
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zeratul976@hotmail.com


The following code compiles with GCC 4.8 and earlier:


template <typename T>
struct A
{
    typedef typename T::type type;
};

template <typename T, typename U = A<int>()>
struct C;

template <typename T>
struct C<T>
{

};

C<int> c;


but fails to compile with GCC 4.9 (2013-04-07 snapshot) with the following
error:

test.cpp: In instantiation of 'struct A<int>':
test.cpp:16:8:   required from here
test.cpp:4:30: error: 'int' is not a class, struct, or union type
     typedef typename T::type type;
                              ^


It seems that GCC 4.9 is instantiating A<int>, the return type of the function
type A<int>() which is the default argument for C's template parameter U, while
GCC 4.8 and earlier was not instantiating this class.

The error also has something to do with the presence of the partial
specialization of C, because removing it (and giving the primary template a
definition instead) makes it go away.

[Bug c++/56886] [4.9 regression] undesirable instantiation of class template default argument

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56886

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.9.0

[Bug c++/56886] [4.9 regression] undesirable instantiation of class template default argument

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56886

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|                            |DUPLICATE

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2013-04-09 12:32:58 UTC ---
Yes.

*** This bug has been marked as a duplicate of bug 56838 ***