[Bug c++/72763] New: incorrectly accepts invalid C++11 code that instantiates a non-template class

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72763

            Bug ID: 72763
           Summary: incorrectly accepts invalid C++11 code that
                    instantiates a non-template class
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

It affects 4.8.x and later, and is correctly rejected by 4.7.x. 


$ g++-trunk -v
Using built-in specs.
COLLECT_GCC=g++-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 7.0.0 20160731 (experimental) [trunk revision 238915] (GCC) 
$ 
$ g++-trunk -c -Wall -Wextra -std=c++11 small.cpp
$ clang++-3.8 -c -std=c++11 small.cpp
small.cpp:3:25: error: 'D' following the 'template' keyword does not refer to a
template
template < typename T > using C = typename A < T >::template D < T >; 
                        ^~~~~
small.cpp:7:14: note: in instantiation of template type alias 'C' requested
here
  struct D : C < T > {}; 
             ^
1 error generated.
$ 
$ g++-4.7 -c -std=c++11 small.cpp
small.cpp:3:69: error: ‘typename A< <template-parameter-1-1> >::D’ names
‘struct A< <template-parameter-1-1> >::D’, which is not a class template
$ 


-----------------------------------------------------------------------


template < typename > struct A; 

template < typename T > using C = typename A < T >::template D < T >; 

template < typename T > struct A 
{
  struct D : C < T > {}; 
};

A < int > a;