Support external pybind11

[musicinmybrain]

In general, pybind11 supports use with add_subdirectory(extern/pybind11) or from an install with find_package(pybind11 CONFIG) (https://pybind11.readthedocs.io/en/stable/cmake/index.html, https://pybind11.readthedocs.io/en/stable/compiling.html#building-with-cmake).

I’ve tried to do this downstream in Fedora Linux, but couldn’t manage to untangle CMake enough to get it working properly in this particular case. An EXTERNAL_PYBIND11 option, similar to the existing EXTERNAL_HIGHFIVE, would be a big help!

This isn’t a critical issue, as Fedora Linux guidelines do allow us to continue to bundle pybind11 as long as upstream does not support building with an external copy.

[mgeplf]

That seems reasonable; on the one hand it's a header only library, but on the other I appreciate people who are doing the heavy lifting of packaging things.

This isn’t a critical issue,

Is there a timeline for that, so I can prioritize it appropriately? I'm pretty overwhelmed at the moment.

Thanks!

[musicinmybrain]

I would put it at a low or background priority, with no particular timeline.

There are benefits to unbundling in a distribution, but in cases like this one where there’s no clear way to use the external library, it’s perfectly acceptable for the Fedora package to keep using the bundled library.

Thanks for considering the idea!

[musicinmybrain]

Thank you!