Ability to set environment variables in pyproject.toml

[jabraham17]

The chapel team has switched the build process for some of our developer tools to use scikit-build, but we are now running into issues configuring the build on some machines.

In our CMakeLists.txt file, we invoke an external script that determines the correct system compiler to use. But we are finding on some systems that it is being messed up by sckikit-build setting CC/CXX (even when the user didn't set them). This was done by @henryiii in #782 to fix fortran builds, but it is resulting in CC/CXX being set to invalid values. We would like to be able to opt-out of this behavior.

Currently, this can be achieved by doing CC=$(CC) CXX=$(CXX) pip install ., so that CC/CXX are present in the environment and set to their current value, if they have one.

Is there a way to specify environment variables like this to opt out of CC/CXX being inferred? Either indirectly by setting CC/CXX in pyproject.toml or directly.

For example:

[tool.scikit-build.environment]
CC=...
CXX=...

OR

[tool.scikit-build]
infer-cc = false

If such a feature doesn't exist, can it please be added. Alternatively, please suggest other ways to workaround this problem. We would like to avoid having users have to manually set CC/CXX

[LecrisUT]

Thanks for the breakdown. The second option makes sense to me. Can you check #1050 and suggest an interface that would fit alongside the options proposed there?

[jabraham17]

Perhaps something analogous to cmake.python-hints? cmake.cc-hints? I feel like that meshes well with the cmake toolchain files, as setting CC/CXX unexpectedly might interact badly with them.