WIP Add recipe for cxxwrap

[SylvainCorlay]

The CxxWrap package by @barche is to Julia what boost.python and pybind11 are to Python.

The goal of this PR is to explore how Julia native extensions can be packaged for conda (and other general-purpose package managers). It is now possible since Julia was packaged for conda-forge (cf #3503) thanks to the hard work of @dfornika, and others who worked on the massive PR (@bgruening, @tkelman, @acaprez).

This is work in progress, now only packaging the C++ part (jlcxx).

Ideally, I would like the conda package to differ from the julia package in that jlcxx would be installed in the general prefix instead of being vendored under the julia directory.

This poses two questions for CxxWrap:

• should we add a flag (e.g. with an environment variable) to prevent the CxxWrap Julia package to vendor jlcxx headers.
• should CxxWrap and jlcxx be two separate packages from a conda viewpoint?

Ping @barche.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/CxxWrap) and found it was in an excellent condition.

[SylvainCorlay]

An approach that I am thinking of is to open a PR to the upstream CxxWrap repository, temporarily point to my fork in this PR, so that we can iterate on the changes to build.jl in the fork.

[barche]

Sure, support for a separate jlcxx binary should be doable. We would need a way for the CxxWrap Julia package to check that the binary is compatible with the Julia side, though (i.e. a kind of versioning scheme).

[SylvainCorlay]

I guess I will keep jlcxx and cxxwrap together in a single package for now. From what we learn in doing that, we might want to separate things later.

[jakirkham]

Does it make sense to even include this yet if we are not building on Windows?

[jakirkham]

Could also split them and provide a metpackage that pulls in both components.

[SylvainCorlay]

I think that eventually it should build on windows. I am testing with a local windows install of julia.

[jakirkham]

Opened issue ( conda-forge/julia-feedstock#14 ) to discuss how we want to handle Julia packages with conda. Would love for people interested in this PR and adding other Julia packages to conda-forge to join in the discussion.

[jakirkham]

Should add that Julia seems to place packages in a directory that specifies the major minor version of Julia used. So we might need matrix builds or something like this.

[SylvainCorlay]

Closing now that CxxWrap was successfully split into a pure C++ package and a Julia package.