Making cross-platform wheels

[rth]

As mentioned by @scopatz in #38,

Right now, we need to run conda-press on the target platform. [...] proper toolchain is not available to rewrite the binaries with [otherwise]

and

But then running it with --subdir win-64 on Linux seems to work?

think that is a short term thing because we are not yet stripping binaries for Windows packages (mostly because I don't know how). Once that is added, I wouldn't expect it to work on Linux or Mac anymore (ref #6)

Thanks for the explanations @scopatz !

I think in the use case of making wheels for a package to upload them on PyPi, it would have been really nice if was possible to do that from a single platform. Otherwise having to setup CI would remove part of advantage of conda-press.

Could you mention blockers for that in this issue (assuming that there would be an option to disable stripping of symbols once that's added)?

If I understand correctly one issue is that patchelf doesn't exist on MacOS while install_name_tool doesn't exist on Linux?

In this particular case, some people have managed to use patchelf on MacOS and the source code of install_name_tool can be found here. I wonder if that could be built on Linux (or if there is another alternative that would work with Mach-O files).

[scopatz]

Thanks for opening this up @rth! I think there are a couple of big issues with cross-building wheels.

1. Binary rewriting tools for changing RPATHS for .so, .lib, .dylib, and .dll files are needed (at least on Linux)
2. There needs to be a way to strip symbols from the above binaries as well.

If you could rely on users having some of these tools on their own platforms, you might be able to get away with running some of these rewrite tools at install time or on-first-use time.

[ihnorton]

conda-build has similar needs, and they use LIEF, which is cross-platform, for some binary rewriting tasks.

(although apparently both LIEF and patchelf are buggy in different ways: https://github.com/conda/conda-build/blob/1bbfc0791bbb86cf719ff7a98313904dcd839805/conda_build/post.py#L424)

[scopatz]

yep, moving to lief is a good step