pass rustflags to isolated environemnt

[n-bes]

What's the problem this feature will solve?

I prepared example rust-lang/rust#129489 and mentioned that CC, CFLAGS passed to isolated environment, but RUSTFLAGS not

Describe the solution you'd like

pass only RUSTFLAGS to

Alternative Solutions

Allow to pip.conf read env variables from global configuration file

Additional context

I try to merge c/rust/python code with specific flags

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

My memory may be wrong, but I don’t recall pip does anything special with CC and CFLAGS. Are you sure this is in pip?

[n-bes]

@uranusjr, Not sure yet. I'm looking for the root cause

[ichard26]

Pip doesn't mess with the RUSTFLAGS environment variable or any other environment variable except for PATH, PYTHONPATH, and PYTHONNOUSERSITE. All other environment variables simply pass-through to the subprocessed called under build isolation.