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

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

msebor at gcc dot gnu.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;
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[Bug c++/72763] incorrectly accepts invalid C++11 code that instantiates a non-template class

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

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-08-01
                 CC|                            |marxin at gcc dot gnu.org
   Target Milestone|---                         |4.9.4
     Ever confirmed|0                           |1

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed.
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[Bug c++/72763] [4.9/5/6/7 Regression] incorrectly accepts invalid C++11 code that instantiates a non-template class

msebor at gcc dot gnu.org
In reply to this post by msebor at gcc dot gnu.org
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72763

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.4                       |5.5

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 4.9 branch is being closed
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[Bug c++/72763] [5/6/7 Regression] incorrectly accepts invalid C++11 code that instantiates a non-template class

msebor at gcc dot gnu.org
In reply to this post by msebor at gcc dot gnu.org
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72763

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |msebor at gcc dot gnu.org
         Depends on|                            |72764
      Known to fail|                            |4.8.5, 4.9.3, 5.3.0, 6.1.0,
                   |                            |7.0

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
The test case was rejected prior to r191412 (see also bug 72764 for an ICE
caused by this commit):

r191412 | jason | 2012-09-17 23:47:35 -0400 (Mon, 17 Sep 2012) | 4 lines

        PR c++/54575
        * pt.c (instantiate_alias_template): New.
        (tsubst): Use it.
        (push_access_scope): Allow TYPE_DECL.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72764
[Bug 72764] [5/6/7 Regression] ICE on invalid C++11 code instantiating an alias
template: tree check: expected class ‘type’, have ‘exceptional’ (error_mark) in
typedef_variant_p, at tree.c:12660
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[Bug c++/72763] [5/6/7 Regression] incorrectly accepts invalid C++11 code that instantiates a non-template class

msebor at gcc dot gnu.org
In reply to this post by msebor at gcc dot gnu.org
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72763

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
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[Bug c++/72763] [5/6/7/8 Regression] incorrectly accepts invalid C++11 code that instantiates a non-template class

msebor at gcc dot gnu.org
In reply to this post by msebor at gcc dot gnu.org
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72763

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |jason at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
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[Bug c++/72763] [5/6/7/8 Regression] incorrectly accepts invalid C++11 code that instantiates a non-template class

msebor at gcc dot gnu.org
In reply to this post by msebor at gcc dot gnu.org
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72763

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
This looks well-formed to me; we don't substitute into C<T> until we need D to
be complete, which we don't when we're just using A<int>.  If you change the
declaration of a to

A<int>::D a;

then you get the error you're expecting.
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[Bug c++/72763] [5/6/7/8 Regression] incorrectly accepts invalid C++11 code that instantiates a non-template class

msebor at gcc dot gnu.org
In reply to this post by msebor at gcc dot gnu.org
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72763
Bug 72763 depends on bug 72764, which changed state.

Bug 72764 Summary: [7 Regression] ICE on invalid C++11 code instantiating an alias template: tree check: expected class ‘type’, have ‘exceptional’ (error_mark) in typedef_variant_p, at tree.c:12660
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72764

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED