[Bug c++/64063] New: Incorrect "ambiguous template specialization" error

[Bug c++/64063] New: Incorrect "ambiguous template specialization" error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063

            Bug ID: 64063
           Summary: Incorrect "ambiguous template specialization" error
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org

G++ rejects this explicit instantiation definition as ambiguous:

template<typename T>
struct S
{
  void foo(int) { }
  template<typename U> void foo(U) { }
};

template void S<char>::foo(int);  // XXX


EDG thinks it's OK, clang crashes, and G++ says:


inst.cc:8:15: error: ambiguous template specialization ‘foo<>’ for ‘void
S<char>::foo(int)’
 template void S<char>::foo(int);  // XXX
               ^
inst.cc:4:8: note: candidates are: void S<T>::foo(int) [with T = char]
   void foo(int) { }
        ^
inst.cc:5:29: note:                 template<class U> void S<T>::foo(U) [with U
= U; T = char]
   template<typename U> void foo(U) { }
                             ^


I think EDG is correct and the diagnostic is wrong, because I'm not referring
to any foo<> but rather foo.


Changing the instantiation to be unambiguously a template produces almost the
same error (with foo<> replaced by foo<int>) and that definitely isn't
ambiguous because one candidate isn't even a function template:

template<typename T>
struct S
{
  void foo(int) { }
  template<typename U> void foo(U) { }
};

template void S<char>::foo<int>(int);  // XXX


inst.cc:8:15: error: ambiguous template specialization ‘foo<int>’ for ‘void
S<char>::foo(int)’
 template void S<char>::foo<int>(int);  // XXX
               ^
inst.cc:4:8: note: candidates are: void S<T>::foo(int) [with T = char]
   void foo(int) { }
        ^
inst.cc:5:29: note:                 template<class U> void S<T>::foo(U) [with U
= U; T = char]
   template<typename U> void foo(U) { }
                             ^
>From gcc-bugs-return-468449-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Nov 24 23:38:12 2014
Return-Path: <gcc-bugs-return-468449-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Delivered-To: listarch-gcc-bugs@gcc.gnu.org
Received: (qmail 11594 invoked by alias); 24 Nov 2014 23:38:12 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Delivered-To: mailing list gcc-bugs@gcc.gnu.org
Received: (qmail 11566 invoked by uid 48); 24 Nov 2014 23:38:09 -0000
From: "ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ada/64057] Overlapping memcpy generated for array assignment
Date: Mon, 24 Nov 2014 23:38:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: ada
X-Bugzilla-Version: 4.9.2
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: ebotcazou at gcc dot gnu.org
X-Bugzilla-Status: WAITING
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: bug_status cf_reconfirmed_on cc everconfirmed
Message-ID: <bug-64057-4-KS74Lj1BGn@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-64057-4@http.gcc.gnu.org/bugzilla/>
References: <bug-64057-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2014-11/txt/msg02921.txt.bz2
Content-length: 691

https://gcc.gnu.org/bugzilla/show_bug.cgi?idd057

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2014-11-24
                 CC|                            |ebotcazou at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> Let me know if you need more info

We need a testcase that fails with GCC 4.8 or GCC 4.9 since xsinfo is built by
the base compiler.

[Bug c++/64063] Incorrect "ambiguous template specialization" error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Apparently EDG instantiates the member function template, which is not what I
wanted:

template<typename T>
struct S
{
  void foo(int) { }
  template<typename U> void foo(U);  // undefined
};

template void S<char>::foo(int);  // XXX


"inst.cc", line 8: error: function "S<T>::foo(U) [with T=char, U=int]" cannot
          be instantiated -- no template definition was supplied
  template void S<char>::foo(int);  // XXX
           ^

Is there no syntax for instantiating the non-template?

[Bug c++/64063] [DR 1665] Incorrect "ambiguous template specialization" error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |SUSPENDED
   Last reconfirmed|                            |2014-11-25
            Summary|Incorrect "ambiguous        |[DR 1665] Incorrect
                   |template specialization"    |"ambiguous template
                   |error                       |specialization" error
     Ever confirmed|0                           |1

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
At http://llvm.org/bugs/show_bug.cgi?id=21661 Richard identified this as
http://open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1665

[Bug c++/64063] [DR 1665] Incorrect "ambiguous template specialization" error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The current handling of the following is still wrong (rejects-valid)
independent of DR 1665. It should compile because it can only refer to the
template:

template<typename T>
struct S
{
  void foo(int);
  template<typename U> void foo(U) { }
};

template void S<char>::foo<>(int);

[Bug c++/64063] [DR 1665] Incorrect "ambiguous template specialization" error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|SUSPENDED                   |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 39270.

*** This bug has been marked as a duplicate of bug 39270 ***

[Bug c++/64063] [DR 1665] Incorrect "ambiguous template specialization" error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|DUPLICATE                   |---
             Status|RESOLVED                    |NEW

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reopening.

[Bug c++/64063] [DR 1665] Incorrect "ambiguous template specialization" error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64063

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fchelnokov at gmail dot com

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 104204 has been marked as a duplicate of this bug. ***