[Bug c++/65750] New: miss interpret in a virtual member function with a C++11 style function signature

[Bug c++/65750] New: miss interpret in a virtual member function with a C++11 style function signature

[usagi at WonderRabbitProject dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

            Bug ID: 65750
           Summary: miss interpret in a virtual member function with a
                    C++11 style function signature
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: usagi at WonderRabbitProject dot net

Repro:

#include <functional>

class a
{
  virtual auto f( std::function< void () > ) -> void;
  virtual auto g( std::function< auto () -> void > ) -> void;
};

auto main() -> int { }


Result 1 ( g++-5.0.0, 4.9.2 and >= 4.9.0 ):

prog.cc:6:16: error: implicit templates may not be 'virtual'
   virtual auto g( std::function< auto () -> void > ) -> void;

Result 2 ( g++-4.8.2, g++4.7.3 ):

(no errors, compile is succeed.)

Result 3 ( clang++-3.7.0, 3.6.0, 3.5.0 and 3.4 )

(no errors, compile is succeed.)

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-04-13
      Known to work|                            |4.8.3
            Summary|miss interpret in a virtual |[4.9/5 Regression]
                   |member function with a      |misinterpret in a virtual
                   |C++11 style function        |member function with a
                   |signature                   |C++11 style function
                   |                            |signature
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Rejects-valid, introduced by support for C++14 return type deduction.


Reduced:

template<typename T> struct F { };

class a
{
  virtual auto f( F< void () > ) -> void;
  virtual auto g( F< auto () -> void > ) -> void;
};

auto main() -> int { }



The error in comment 0 is only on the 4.9 branch, 5.0 gives a different error:

s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
   virtual auto g( F< auto () -> void > ) -> void;
                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
s.cc:6:38: error: template argument 1 is invalid
   virtual auto g( F< auto () -> void > ) -> void;
                                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
   virtual auto g( F< auto () -> void > ) -> void;
                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
s.cc:6:38: error: template argument 1 is invalid
   virtual auto g( F< auto () -> void > ) -> void;
                                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
   virtual auto g( F< auto () -> void > ) -> void;
                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
s.cc:6:38: error: template argument 1 is invalid
   virtual auto g( F< auto () -> void > ) -> void;
                                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
   virtual auto g( F< auto () -> void > ) -> void;
                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
s.cc:6:38: error: template argument 1 is invalid
   virtual auto g( F< auto () -> void > ) -> void;
                                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
   virtual auto g( F< auto () -> void > ) -> void;
                      ^
s.cc:6:22: error: use of ‘auto’ in parameter declaration only available with
-std=c++14 or -std=gnu++14
s.cc:6:38: error: template argument 1 is invalid
   virtual auto g( F< auto () -> void > ) -> void;
                                      ^
s.cc:6:19: error: ‘F’ is not a type
   virtual auto g( F< auto () -> void > ) -> void;
                   ^
s.cc:6:20: error: expected ‘,’ or ‘...’ before ‘<’ token
   virtual auto g( F< auto () -> void > ) -> void;
                    ^
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idI551

prathamesh3492 at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|2015-03-23 00:00:00         |2015-04-13
                 CC|                            |charles.baylis at linaro dot org,
                   |                            |mkuvyrkov at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #4 from prathamesh3492 at gcc dot gnu.org ---
Hi,
The ICE is not reproducible on the trunk any more. git bisect shows
it became non-reproducible after r221297.

Thank you,
Prathamesh

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |abutcher at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
I think this is from the generic lambda/implicit template work rather than
return type deduction.

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[abutcher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

--- Comment #3 from Adam Butcher <abutcher at gcc dot gnu.org> ---
Agreed.  Upon seeing the 'auto' in the parameter list, we'll synthesize a
template parameter for 'g'.  I think Paolo added the diagnostic for virtual to
fix an ICE.

I'm not sure immediately how to handle this one.  For function pointer types
"auto (" should have this behavior.  Maybe we need a bit of look-ahead to solve
this (either for a function pointer or the trailing return arrow).

Looks like trying to tie down semantics at parse time is biting us again.

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
It started to be rejected with r204714, and since r218879 there are lost of
errors instead of just one warning and one error.

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot com

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Out of curiosity, what happened to the work linked in Comment #5? I see an Ok
and then nothing more?

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed in trunk so far.

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

--- Comment #9 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Mon Jun 29 09:34:58 2015
New Revision: 225114

URL: https://gcc.gnu.org/viewcvs?rev=225114&root=gcc&view=rev
Log:
/cp
2015-06-29  Adam Butcher  <adam@jessamine.co.uk>

        PR c++/65750
        * parser.c (cp_parser_simple_type_specifier): Don't synthesize
        implicit template parm if 'auto' is a placeholder for trailing
        return type.

/testsuite
2015-06-29  Adam Butcher  <adam@jessamine.co.uk>

        PR c++/65750
        * g++.dg/cpp0x/trailing11.C: New.

Added:
    branches/gcc-5-branch/gcc/testsuite/g++.dg/cpp0x/trailing11.C
Modified:
    branches/gcc-5-branch/gcc/cp/ChangeLog
    branches/gcc-5-branch/gcc/cp/parser.c
    branches/gcc-5-branch/gcc/testsuite/ChangeLog

[Bug c++/65750] [4.9/5 Regression] misinterpret in a virtual member function with a C++11 style function signature

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.2

--- Comment #10 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 5.2 too.