Warnings: Unused & Offsetof

[ax3l]

Thx for the great project! ✨

During compile I get several warnings about:

• unused vars in

./include/pybind11/attr.h(257)
./include/pybind11/attr.h(265)
./include/pybind11/attr.h(269)

• and an other in

./include/pybind11/pybind11.h(566): warning: offsetof applied to non-POD types is nonstandard

Tested with master as of 48548ea, nvcc/7.5.17 & gcc/4.9.2.

[ax3l]

thank you, wonderful! ✨

[ax3l]

@wjakob I am sorry but I think your change introduced even more warnings in gcc-4.8 since the pragma -Wno-invalid-offsetof is not (yet) known in it:
https://travis-ci.org/ax3l/pybind11/jobs/103239618#L518

For the unused warning it is my fault, I did forget to paste the full warning (sorry!). It is the var unused itself that is marked as unused:
https://travis-ci.org/ax3l/pybind11/jobs/103239619#L544

[wjakob]

Can you post a PR for the fix in this case? Thanks!

[ax3l]

I will create a nvcc CI PR for the issue first so you it's documented and reproducible and then I will send a follow up PR with a fix if you like!

The reason for that order is that I will modify the CMakeLists.txt twice in the process.

[ax3l]

P.S.: Can't we make instance<void> an actual POD type instead of removing the warning? offsetof is actually really undefined by the standard on non standard layout types.

[wjakob]

ok, I think I fixed the offsetoff issue in the last commit. The warning about unused does not make any sense to me -- how can it complain if there is a (void) unused; statement? That is basically an explicit instruction not to complain :)

[wjakob]

Any idea about the warnings with regards to unused? Is this a compiler issue?

[ax3l]

oh great, you fixed the POD/offsetof implementation in 88d1d04 and it works! (I tested it again just now.)

[ax3l]

I think the problem with unused is actually, that it is really not used? (Besides the (void) thingy.).
I have to admit, I don't get to my full understanding what that class and assignment actually does.

This is the full warning:

pybind11/attr.h(265): warning: variable "unused" was set but never used
          detected during:
            instantiation of "void pybind11::detail::process_attributes<Args...>::precall(pybind11::handle) [with Args=<>]" 
pybind11/pybind11.h(139): here
            instantiation of "void pybind11::cpp_function::initialize(Func &&, Return (*)(Args...), const Extra &...) [with Func=lambda [](pybind11::handle)->void, Return=void, Args=<pybind11::handle>, Extra=<>]" 
pybind11/pybind11.h(91): here
            instantiation of "pybind11::cpp_function::cpp_function(Func &&, const Extra &...) [with Func=lambda [](pybind11::handle)->void, Extra=<>]" 
pybind11/pybind11.h(952): here

pybind11/attr.h(269): warning: variable "unused" was set but never used
          detected during:
            instantiation of "void pybind11::detail::process_attributes<Args...>::postcall(pybind11::handle, pybind11::handle) [with Args=<>]" 
pybind11/pybind11.h(147): here
            instantiation of "void pybind11::cpp_function::initialize(Func &&, Return (*)(Args...), const Extra &...) [with Func=lambda [](pybind11::handle)->void, Return=void, Args=<pybind11::handle>, Extra=<>]" 
pybind11/pybind11.h(91): here
            instantiation of "pybind11::cpp_function::cpp_function(Func &&, const Extra &...) [with Func=lambda [](pybind11::handle)->void, Extra=<>]" 
pybind11/pybind11.h(952): here

pybind11/attr.h(257): warning: variable "unused" was set but never used
          detected during:
            instantiation of "void pybind11::detail::process_attributes<Args...>::init(const Args &..., pybind11::detail::function_record *) [with Args=<>]" 
pybind11/pybind11.h(153): here
            instantiation of "void pybind11::cpp_function::initialize(Func &&, Return (*)(Args...), const Extra &...) [with Func=lambda [](pybind11::handle)->void, Return=void, Args=<pybind11::handle>, Extra=<>]" 
pybind11/pybind11.h(91): here
            instantiation of "pybind11::cpp_function::cpp_function(Func &&, const Extra &...) [with Func=lambda [](pybind11::handle)->void, Extra=<>]" 
pybind11/pybind11.h(952): here

pybind11/attr.h(265): warning: variable "unused" was set but never used
          detected during:
            instantiation of "void pybind11::detail::process_attributes<Args...>::precall(pybind11::handle) [with Args=<>]" 
pybind11/pybind11.h(139): here
            instantiation of "void pybind11::cpp_function::initialize(Func &&, Return (*)(Args...), const Extra &...) [with Func=lambda [](pybind11::handle)->void, Return=void, Args=<pybind11::handle>, Extra=<>]" 
pybind11/pybind11.h(91): here
            instantiation of "pybind11::cpp_function::cpp_function(Func &&, const Extra &...) [with Func=lambda [](pybind11::handle)->void, Extra=<>]" 
pybind11/pybind11.h(952): here

pybind11/attr.h(269): warning: variable "unused" was set but never used
          detected during:
            instantiation of "void pybind11::detail::process_attributes<Args...>::postcall(pybind11::handle, pybind11::handle) [with Args=<>]" 
pybind11/pybind11.h(147): here
            instantiation of "void pybind11::cpp_function::initialize(Func &&, Return (*)(Args...), const Extra &...) [with Func=lambda [](pybind11::handle)->void, Return=void, Args=<pybind11::handle>, Extra=<>]" 
pybind11/pybind11.h(91): here
            instantiation of "pybind11::cpp_function::cpp_function(Func &&, const Extra &...) [with Func=lambda [](pybind11::handle)->void, Extra=<>]" 
pybind11/pybind11.h(952): here

pybind11/attr.h(257): warning: variable "unused" was set but never used
          detected during:
            instantiation of "void pybind11::detail::process_attributes<Args...>::init(const Args &..., pybind11::detail::function_record *) [with Args=<>]" 
pybind11/pybind11.h(153): here
            instantiation of "void pybind11::cpp_function::initialize(Func &&, Return (*)(Args...), const Extra &...) [with Func=lambda [](pybind11::handle)->void, Return=void, Args=<pybind11::handle>, Extra=<>]" 
pybind11/pybind11.h(91): here
            instantiation of "pybind11::cpp_function::cpp_function(Func &&, const Extra &...) [with Func=lambda [](pybind11::handle)->void, Extra=<>]" 
pybind11/pybind11.h(952): here

[ax3l]

found a solution, will send a PR