[Bug c++/30857] New: accepts both explicit instantiation and explicit specialization, duplicate explicit instantiations, etc.

["bkoz at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

I thought g++ used to warn for this:

template <typename T>
class foo { };

template<> class foo<int> { };

template class foo<int>;

Where the error was something informative like "one may not explicitly
specialize and explicitly instantiate" blah blah blah

However, mainline currently does not do this.

>From 14.7

-5- No program shall explicitly instantiate any template more than once, both
explicitly instantiate and explicitly specialize a template, or specialize a
template more than once for a given set of template-arguments. An
implementation is not required to diagnose a violation of this rule.

So, this is not required by the standard. As a QoI issue, however, this would
be  beneficial. 

Here's why I wanted this: if one is doing API testing, and the API requires
explicit specializations, than one possible negative test is to explicitly
instantiate the required specialization and get an error. 

Otherwise, I suppose another neg test is to redefine the specialization. This
is also not required to give an error, but current g++ does (redefinition
error). 

Note also, no diagnostic for duplicate explicit instantiations:

template <typename T>
class foo { };

template class foo<int>;
template class foo<int>;


Either of these or all may be a warning regressions (if my mind is not playing
tricks on me.)

I have not tested with other compilers, or previous g++ versions.

Consistent behavior for all three cases would be appreciated.


-- 
           Summary: accepts both explicit instantiation and explicit
                    specialization, duplicate explicit instantiations, etc.
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bkoz at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30857