[Bug libstdc++/61947] New: Ambiguous calls when constructing std::tuple

[Bug libstdc++/61947] New: Ambiguous calls when constructing std::tuple

[roman.perepelitsa at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

            Bug ID: 61947
           Summary: Ambiguous calls when constructing std::tuple
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roman.perepelitsa at gmail dot com

#include <tuple>

struct ConvertibleToAny {
  template <class T> operator T() const { return T(); }
};

int main() {
  std::tuple<ConvertibleToAny&&> t(ConvertibleToAny{});
}

Produces:

third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:262:4:
error: call to constructor of '_Head_base<0UL, (anonymous
namespace)::ConvertibleToAny &&, __empty_not_final<ConvertibleToAny
&&>::value>' is ambiguous
          _Base(std::forward<_UHead>(__head)) { }
          ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:405:4:
note: in instantiation of function template specialization 'std::_Tuple_impl<0,
(anonymous namespace)::ConvertibleToAny &&>::_Tuple_impl<(anonymous
namespace)::ConvertibleToAny, void>' requested here
        : _Inherited(std::forward<_UElements>(__elements)...) { }
          ^
experimental/users/romanp/tuple_bug/tuple-bug.cc:13:34: note: in instantiation
of function template specialization 'std::tuple<(anonymous
namespace)::ConvertibleToAny &&>::tuple<(anonymous
namespace)::ConvertibleToAny, void>' requested here
  std::tuple<ConvertibleToAny&&> t(ConvertibleToAny{});
                                 ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:128:12:
note: candidate is the implicit move constructor
    struct _Head_base<_Idx, _Head, false>
           ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:128:12:
note: candidate constructor (the implicit copy constructor) has been implicitly
deleted
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:142:7:
note: candidate constructor
      _Head_base(__uses_alloc0)

The call shouldn't be ambiguous. It should pick the following constructor:

[tuple.cnstr]

  template <class... UTypes>
  explicit tuple(UTypes&&... u);

  Requires: sizeof...(Types) == sizeof...(UTypes). is_constructible<Ti , Ui
&&>::value is true for all i.
  Effects: Initializes the elements in the tuple with the corresponding value
in std::forward<UTypes>(u).

is_constructible<ConvertibleToAny&&, ConvertibleToAny&&>::value is true, so the
precondition is satisfied.

This bug affects std::bind as it's built on top of std::tuple.

#include <functional>

struct ConvertibleToAny {
  template <class T> operator T() const { return T(); }
};

void Sink(int) {}

int main() {
  std::bind(Sink, std::placeholders::_1)(ConvertibleToAny{});
}

Error:

third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:262:4:
error: call to constructor of '_Head_base<0UL, (anonymous
namespace)::ConvertibleToAny &&, __empty_not_final<ConvertibleToAny
&&>::value>' is ambiguous
          _Base(std::forward<_UHead>(__head)) { }
          ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:405:4:
note: in instantiation of function template specialization 'std::_Tuple_impl<0,
(anonymous namespace)::ConvertibleToAny &&>::_Tuple_impl<(anonymous
namespace)::ConvertibleToAny, void>' requested here
        : _Inherited(std::forward<_UElements>(__elements)...) { }
          ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:868:14:
note: in instantiation of function template specialization
'std::tuple<(anonymous namespace)::ConvertibleToAny &&>::tuple<(anonymous
namespace)::ConvertibleToAny, void>' requested here
    { return tuple<_Elements&&...>(std::forward<_Elements>(__args)...); }
             ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/functional:1354:13:
note: in instantiation of function template specialization
'std::forward_as_tuple<(anonymous namespace)::ConvertibleToAny>' requested here
              std::forward_as_tuple(std::forward<_Args>(__args)...),
                   ^
experimental/users/romanp/tuple_bug/tuple-bug.cc:15:41: note: in instantiation
of function template specialization 'std::_Bind<void
(*(std::_Placeholder<1>))(int)>::operator()<(anonymous
namespace)::ConvertibleToAny, void>' requested here
  std::bind(Sink, std::placeholders::_1)(ConvertibleToAny{});
                                        ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:128:12:
note: candidate is the implicit move constructor
    struct _Head_base<_Idx, _Head, false>
           ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:128:12:
note: candidate constructor (the implicit copy constructor) has been implicitly
deleted
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:142:7:
note: candidate constructor
      _Head_base(__uses_alloc0)
      ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:271:2:
error: call to constructor of '_Head_base<0UL, (anonymous
namespace)::ConvertibleToAny &&, __empty_not_final<ConvertibleToAny
&&>::value>' is ambiguous
        _Base(std::forward<_Head>(_M_head(__in))) { }
        ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:409:17:
note: in instantiation of member function 'std::_Tuple_impl<0, (anonymous
namespace)::ConvertibleToAny &&>::_Tuple_impl' requested here
      constexpr tuple(tuple&&) = default; 
                ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/functional:1354:13:
note: in instantiation of function template specialization
'std::forward_as_tuple<(anonymous namespace)::ConvertibleToAny>' requested here
              std::forward_as_tuple(std::forward<_Args>(__args)...),
                   ^
experimental/users/romanp/tuple_bug/tuple-bug.cc:15:41: note: in instantiation
of function template specialization 'std::_Bind<void
(*(std::_Placeholder<1>))(int)>::operator()<(anonymous
namespace)::ConvertibleToAny, void>' requested here
  std::bind(Sink, std::placeholders::_1)(ConvertibleToAny{});
                                        ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:128:12:
note: candidate is the implicit move constructor
    struct _Head_base<_Idx, _Head, false>
           ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:128:12:
note: candidate constructor (the implicit copy constructor) has been implicitly
deleted
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:142:7:
note: candidate constructor
      _Head_base(__uses_alloc0)
      ^
third_party/crosstool/v17/stable/gcc-x86_64-grtev3-linux-gnu/x86_64-grtev3-linux-gnu/include/c++/4.8.x-google/tuple:868:14:
note: implicit move constructor for 'std::tuple<(anonymous
namespace)::ConvertibleToAny &&>' first required here
    { return tuple<_Elements&&...>(std::forward<_Elements>(__args)...); }
             ^

This bug appears to be a regression from libstdc++ 4.6, where the code was
accepted.

[Bug libstdc++/61947] [4.8/4.9/4.10 Regression] Ambiguous calls when constructing std::tuple

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-07-29
      Known to work|                            |4.6.4
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org
            Summary|Ambiguous calls when        |[4.8/4.9/4.10 Regression]
                   |constructing std::tuple     |Ambiguous calls when
                   |                            |constructing std::tuple
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
stupid allocators

[Bug libstdc++/61947] [4.8/4.9/4.10 Regression] Ambiguous calls when constructing std::tuple

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Created attachment 33203
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33203&action=edit
proposed patch

Add std::allocator_arg_t parameter to unary _Head_base constructors taking a
__uses_allocN tag type, so that they are not candidates for calls with one
parameter. This allows the !is_convertible constraint to be removed from the
_Head_base::_Head_base(__UHead&&) constructor.

[Bug libstdc++/61947] [4.8/4.9/4.10 Regression] Ambiguous calls when constructing std::tuple

[ppluzhnikov at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

Paul Pluzhnikov <ppluzhnikov at google dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppluzhnikov at google dot com

--- Comment #3 from Paul Pluzhnikov <ppluzhnikov at google dot com> ---
Google ref: b/16644819

[Bug libstdc++/61947] [4.8/4.9/4.10 Regression] Ambiguous calls when constructing std::tuple

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Tue Jul 29 17:30:34 2014
New Revision: 213221

URL: https://gcc.gnu.org/viewcvs?rev=213221&root=gcc&view=rev
Log:
    PR libstdc++/61947
    * include/std/tuple (_Head_base): Use allocator_arg_t parameters to
    disambiguate unary constructors.
    (_Tuple_impl): Pass allocator_arg_t arguments.
    * testsuite/20_util/tuple/61947.cc: New.
    * testsuite/20_util/uses_allocator/cons_neg.cc: Adjust dg-error line.

Added:
    trunk/libstdc++-v3/testsuite/20_util/tuple/61947.cc
      - copied, changed from r213220,
trunk/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/std/tuple
    trunk/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc

[Bug libstdc++/61947] [4.8/4.9/4.10 Regression] Ambiguous calls when constructing std::tuple

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.10.0

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on the trunk so far.

[Bug libstdc++/61947] [4.8/4.9 Regression] Ambiguous calls when constructing std::tuple

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.8.4

[Bug libstdc++/61947] [4.8/4.9 Regression] Ambiguous calls when constructing std::tuple

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Sat Dec  6 20:38:01 2014
New Revision: 218453

URL: https://gcc.gnu.org/viewcvs?rev=218453&root=gcc&view=rev
Log:
    PR libstdc++/61947
    * include/std/tuple (_Head_base): Use allocator_arg_t parameters to
    disambiguate unary constructors.
    (_Tuple_impl): Pass allocator_arg_t arguments.
    * testsuite/20_util/tuple/61947.cc: New.
    * testsuite/20_util/uses_allocator/cons_neg.cc: Adjust dg-error line.

Added:
    branches/gcc-4_8-branch/libstdc++-v3/testsuite/20_util/tuple/61947.cc
      - copied, changed from r218452,
branches/gcc-4_8-branch/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
Modified:
    branches/gcc-4_8-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_8-branch/libstdc++-v3/include/std/tuple
   
branches/gcc-4_8-branch/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc

[Bug libstdc++/61947] [4.8/4.9 Regression] Ambiguous calls when constructing std::tuple

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Sat Dec  6 22:24:16 2014
New Revision: 218457

URL: https://gcc.gnu.org/viewcvs?rev=218457&root=gcc&view=rev
Log:
    PR libstdc++/61947
    * include/std/tuple (_Head_base): Use allocator_arg_t parameters to
    disambiguate unary constructors.
    (_Tuple_impl): Pass allocator_arg_t arguments.
    * testsuite/20_util/tuple/61947.cc: New.
    * testsuite/20_util/uses_allocator/cons_neg.cc: Adjust dg-error line.

Added:
    branches/gcc-4_9-branch/libstdc++-v3/testsuite/20_util/tuple/61947.cc
      - copied, changed from r218456,
branches/gcc-4_9-branch/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
Modified:
    branches/gcc-4_9-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_9-branch/libstdc++-v3/include/std/tuple
   
branches/gcc-4_9-branch/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc

[Bug libstdc++/61947] [4.8/4.9 Regression] Ambiguous calls when constructing std::tuple

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|4.10.0                      |5.0
         Resolution|---                         |FIXED

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed for 4.8.4 and 4.9.3 too