Pedantic Warnings in pytypes.h

[ax3l]

Issue description

Seen with gcc 4.8.5 on Ubuntu 14.04:

include/pybind11/pytypes.h: In lambda function:
include/pybind11/pytypes.h:1100:89: error: ISO C++ forbids casting between pointer-to-function and pointer-to-object [-Werror=pedantic]
             auto destructor = reinterpret_cast<void (*)(void *)>(PyCapsule_GetContext(o));
                                                                                         ^
include/pybind11/pytypes.h: In constructor ‘pybind11::capsule::capsule(const void*, void (*)(void*))’:
include/pybind11/pytypes.h:1108:50: error: ISO C++ forbids casting between pointer-to-function and pointer-to-object [-Werror=pedantic]
         if (PyCapsule_SetContext(m_ptr, (void *) destructor) != 0)
                                                  ^
include/pybind11/pytypes.h: In constructor ‘pybind11::capsule::capsule(void (*)())’:
include/pybind11/pytypes.h:1113:66: error: ISO C++ forbids casting between pointer-to-function and pointer-to-object [-Werror=pedantic]
         m_ptr = PyCapsule_New(reinterpret_cast<void *>(destructor), nullptr, [](PyObject *o) {
                                                                  ^
include/pybind11/pytypes.h: In lambda function:
include/pybind11/pytypes.h:1114:92: error: ISO C++ forbids casting between pointer-to-function and pointer-to-object [-Werror=pedantic]
             auto destructor = reinterpret_cast<void (*)()>(PyCapsule_GetPointer(o, nullptr));

Reproducible example code

Compile a pybind11 2.2.3 example with -pedantic and -Werror and gcc 4.8.5.

[bstaletic]

gcc 4.9 doesn't warn. gcc 4.8 could barely be called a C++11 compiler. Pybind11 headers are now SYSTEM.

@henryiii @ax3l Is this issue still relevant?

[henryiii]

GCC 4.8 is still very important - it's the manylinux1 compiler. But I'm pretty sure at least the SYSTEM will have fixed this for users. We maybe should be compiling with pedantic and maybe even effc++ for GNU. :)

Turning on some extra warnings, I get a shadow warning that's easy to fix, and this:

#define PYBIND11_OVERRIDE(ret_type, cname, fn, ...) \
        ^
../tests/test_virtual_functions.cpp:319:73: warning: must specify at least one argument for '...' parameter of variadic macro [-Wgnu-zero-variadic-macro-arguments]
        A &A_ref() override { PYBIND11_OVERRIDE(A &, OverrideTest, A_ref); }

// Several more, similar
...

../include/pybind11/cast.h:1597:79: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]

[henryiii]

Fixed by renaming to flag_, which has happened at some point.