Set build-time env vars about the current build for scripts to use

[joerick]

We already set CIBUILDWHEEL=1 for our builds, so we could add CIBUILDWHEEL_BUILD_IDENTIFIER - the CIBUILDWHEEL prefix distinguishing these variables from CIBW options.

Originally posted by @joerick in #910 (reply in thread)

Or just CIBUILDWHEEL_BUILD might work.
An arch variable was also mooted, which might be easier to switch on. In this naming structure, that would be CIBUILDWHEEL_BUILD_ARCH

[henryiii]

The build identifier is not singular during the before-all step, though possibly we could set it to a list of build identifiers? That would have the handy feature that the suffix of the list would always be the correct suffix, because that cannot change for a batch.

The BUILD_ARCH would still be handy, especially for build-all, and easier to set. For @hynek's case, though, I'd argue it's the wrong solution - for making decisions inside your Python build backend (setuptools, in this case), you want to avoid CIBW specific controls so that you can also support Conda-build and other build tooling. It's really only for use in before-all and before-build.

[hynek]

I'd be more than more happy to see better solutions – I'm sure I'm not the only one with this problem. :)

If I could just set ARGON2_CFFI_USE_SSE2=0 whenever cross-compiling to non-amd64, that would be even better. Right now, I'm parsing ARCHFLAGS tho which is unfortunate. :D

[henryiii]

If I could just set ARGON2_CFFI_USE_SSE2=0 whenever cross-compiling to non-amd6

I'd say this is a non-ideal solution too, as it requires special setup to cross compile unique to your project. An ideal solution would work if anyone was cross compiling (such as in conda-build, etc), and would not tied to cibuildwheel at all. The ARCHFLAGS is how setuptools is configured to cross-compile on macOS, so I don't think it's bad - using that will work for everyone who tries to cross compile, not just a cibuildwheel setup. I left some comments on improving it, though.

[henryiii]

(Correction: not that bad, didn't really pay attention to what you were specifying with the variable. I'd still say that the default for ARGON2_CFFI_USE_SSE2 should be smart, though, and pick up on cross compiling via ARCHFLAGS.)

[henryiii]

If I could just set ARGON2_CFFI_USE_SSE2=0

I think making this smarter is likely the best way to go, but of course you can do this if you want.

[[tool.cibuildwheel.overrides]]
select = ["*_universal2", "*_arm64"]
environment = {"ARGON2_CFFI_USE_SSE2" = "0"}

Just be warned that this will replace rather than augment your environment if you've set it at any higher cibuildwheel level.

[joerick]

PRs would be welcome for this!