Enable the compilation of pybind11 bindings in CI when conda is used

[GiulioRomualdi]

The first step towards #782

This depends on #936

[traversaro]

Wow, you beat me by three minutes (see #938). Can you also enable the SWIG bindings while you are at it? It should be just necessary to also install swig, and pass -DIDYNTREE_USES_PYTHON:BOOL=ON to the configure step.

[traversaro]

Also here the same problem of #867 appears, probably it is a problem of modern pybind11, not related to pip.

[traversaro]

Indeed, SYSTEM is not a documented option of pybind11_add_module in latest pybind11, see https://pybind11.readthedocs.io/en/stable/compiling.html#pybind11-add-module, probably we can just remove it?

[traversaro]

Indeed, SYSTEM was a completly documented and legal option in pybind11 2.4.3 (the version used in Ubuntu 20.04), see https://github.com/pybind/pybind11/blob/v2.4.3/docs/compiling.rst#pybind11_add_module . Perhaps we are witnessing a rare example of romanata in the wild? @francesco-romano

[traversaro]

Perhaps we are witnessing a rare example of romanata in the wild? @francesco-romano

After thinking about it during dinner, I think it is not a romanata. A romanata is the use of a not strictly necessary (but fully documented and supported) feature that leads to a bug or problem due to some corner case behaviour. In this case, the SYSTEM keyword was deliberatly removed upstream in pybind11, so it is not a corner case behaviour. Furthermore, I guess SYSTEM was added to remove some warning due to pybind11, so probably it was not even not necessary.

[traversaro]

Indeed, SYSTEM is not a documented option of pybind11_add_module in latest pybind11, see https://pybind11.readthedocs.io/en/stable/compiling.html#pybind11-add-module, probably we can just remove it?

Even if it is not documented, SYSTEM is a parsed option (see https://github.com/pybind/pybind11/blob/v2.8.1/tools/pybind11Tools.cmake#L148) so even if we use it it should not result in that error. However, according to pybind/pybind11#2338 :

CMake treats all IMPORTED targets as SYSTEM, so this was/is always on when using configuration mode.

So in any case (even with pybind11 2.4.3) it should not be necessary to use SYSTEM, so we can safely remove it.

[traversaro]

A little bit of magic is still necessary for multi config generators, I can look into it.

[traversaro]

A little bit of magic is still necessary for multi config generators, I can look into it.

The issue is a bit more complicated than I expected, for now I disabled the Python/pybind tests on Windows and I opened an issue #939 to keep track of this.

[GiulioRomualdi]

Since #936 has been merged I think we should rebase the PR on devel

[traversaro]

Since #936 has been merged I think we should rebase the PR on devel

Ack, I can do that.

[traversaro]

Done!

[GiulioRomualdi]

feel free to merge it :)