W_GADGET_IMPL on macOS causes problems

[jcelerier]

Hello,

on macOS (and macOS only - works fine on windows and linux) I'm getting the following problem :

foo.hpp:

struct foo { 
  W_GADGET(foo)
};

foo.cpp:

W_GADGET_IMPL(foo)

bar.hpp

struct bar {
  W_OBJECT(bar)
  public: void doStuff(foo f) W_SIGNAL(doStuff, f);
};

bar.cpp:

W_OBJECT_IMPL(bar)

-> Undefined symbols for architecture x86_64: "foo::staticMetaObject", referenced from: (whatever) bar.cpp

What I suppose is that since the staticMetaObject is constexpr, if it is not being ODR-used in foo.cpp it may not be instantiated at all.

I am supposing this because adding for instance :

auto disregard_me = &foo::staticMetaObject; 

in foo.cpp makes linking work.

I guess another solution would be to put the W_GADGET_IMPL in the header, but I am not sure it is guaranteed to work - is it ?

[ogoffart]

Maybe we should remove the constexpr (can you try removing the W_STATICMETAOBJECT_CONSTEXPR?) We already don't have it constexpr on windows. (for another reason) I hope that it will still be initialized at compile time, even without that constexpr.

Otherwise we could try to add the disregard_me somehow in the macro. (W_OBJECT_IMPL uses it in the metaObject() implementation, i guess that's why it works for W_OBJECT)

[jcelerier]

I tested a bit more and have two observations :

• It works fine with W_STATICMETAOBJECT_CONSTEXPR unset as expected
• It works fine in -std=c++14, the problem only appears at -std=c++17.

Maybe an interesting solution would be to add metaObject() support to Q/W_GADGET ?

[jcelerier]

verdigris-bug.zip in any case here's a simple repro

[ogoffart]

Should be fixed now with the last commit.