My PEX includes a Python package that is only available as an source distribution. I want to influence the build process of the sdist via setting the CMAKE_ARGS environment variable. I tried to export CMAKE_ARGS in the shell used to run Pants which didn't have any effect. I tried to use the "env" kwarg in the pex_binary target, but the values are only applied when the PEX is run (as I expected). I found the python-native-code flags in the docs, but they only allow setting CPPFLAGS and LDFLAGS. Eventually, I tried adding the CMAKE_ARGS via --subprocess-environment-env-vars option (in combination with --no-local-cache) which had no effect either. Do you have any idea what else I could try?

By default, Pants will not forward envvars as part of making hermetic builds.

--subprocess-environment-env-vars

should work for that. I find the syntax is easier to get right if you're setting it in the pants.toml file. You can crack into everything Pants is doing with the

--keep-sandboxes=always

flag, which will keep the sandboxes around. you can at least see if your envvars are making it in.