[Bug c++/67952] New: Compilation error with boost::signals2 and generic lambda: cannot call member function without object

[jens.auer at cgi dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67952

            Bug ID: 67952
           Summary: Compilation error with boost::signals2 and generic
                    lambda: cannot call member function without object
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jens.auer at cgi dot com
  Target Milestone: ---

Created attachment 36495
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36495&action=edit
Preprocessed source code

The following code doesn't compile with boost 1.59 and gcc 5.1, but with clang
3.6:

#include <boost/signals2.hpp>

class A
{
public:
    A()
    {
        // these two work
        sig2.connect( [this]() {f();} );
        sig.connect( [this](auto x) {this->g(x);} );

        // this does not work
        sig.connect( [this](auto x) {g(x);} );
    }


private:
    void f();
    void g(int);

    boost::signals2::signal<void (int)> sig;
    boost::signals2::signal<void ()> sig2;
};

The error message is
shadow.cpp: In instantiation of ‘A::A()::<lambda(auto:2)> [with auto:2 = int]’:
/lhome1/auerj/opt/include/boost/function/function_template.hpp:153:11:  
required from ‘static void
boost::detail::function::void_function_obj_invoker1<FunctionObj, R,
T0>::invoke(boost::detail::function::function_buffer&, T0) [with FunctionObj =
A::A()::<lambda(auto:2)>; R = void; T0 = int]’
/lhome1/auerj/opt/include/boost/function/function_template.hpp:934:38:  
required from ‘void boost::function1<R, T1>::assign_to(Functor) [with Functor =
A::A()::<lambda(auto:2)>; R = void; T0 = int]’
/lhome1/auerj/opt/include/boost/function/function_template.hpp:722:7:  
required from ‘boost::function1<R, T1>::function1(Functor, typename
boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value),
int>::type) [with Functor = A::A()::<lambda(auto:2)>; R = void; T0 = int;
typename
boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value),
int>::type = int]’
/lhome1/auerj/opt/include/boost/function/function_template.hpp:1071:16:  
required from ‘boost::function<R(T0)>::function(Functor, typename
boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value),
int>::type) [with Functor = A::A()::<lambda(auto:2)>; R = void; T0 = int;
typename
boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value),
int>::type = int]’
/lhome1/auerj/opt/include/boost/function/function_template.hpp:1126:5:  
required from ‘typename
boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value),
boost::function<R(T0)>&>::type boost::function<R(T0)>::operator=(Functor) [with
Functor = A::A()::<lambda(auto:2)>; R = void; T0 = int; typename
boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value),
boost::function<R(T0)>&>::type = boost::function<void(int)>&]’
/lhome1/auerj/opt/include/boost/signals2/detail/slot_template.hpp:160:24:  
required from ‘void boost::signals2::slot<R(Args ...),
SlotFunction>::init_slot_function(const F&) [with F = A::A()::<lambda(auto:2)>;
SlotFunction = boost::function<void(int)>; R = void; Args = {int}]’
/lhome1/auerj/opt/include/boost/signals2/detail/slot_template.hpp:85:27:  
required from ‘boost::signals2::slot<R(Args ...), SlotFunction>::slot(const F&)
[with F = A::A()::<lambda(auto:2)>; SlotFunction = boost::function<void(int)>;
R = void; Args = {int}]’
shadow.cpp:13:45:   required from here
shadow.cpp:13:38: error: cannot call member function ‘void A::g(int)’ without
object
         sig.connect( [this](auto x) {g(x);} );

I think it is a compiler bug because adding the implicit this-> solves the
problem (see second connect).

My gcc version:
g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/lhome1/auerj/opt/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-5.1.0/configure --prefix=/lhome1/auerj/opt
--enable-languages=c,c++
Thread model: posix
gcc version 5.1.0 (GCC) 

I have attached the preprocessed output so it should be easy to reproduce the
issue.

It is probably a duplicate of 61636, but I such that it can be tracked as such.
I guess boost::signals2 is a popular library, so it may be worth to have it in
the database explicitly.