Improve documentation, for systems where python3 points to python<3.7

[pfbuxton]

rust-analyzer version: rust-analyzer version: 0.3.2433-standalone

rustc version: 1.86.0 (05f9846f8 2025-03-31)

editor or extension: VSCode

relevant settings: rust-analyzer.server.extraEnv, PYO3_CROSS_LIB_DIR

I am working on a project which uses PyO3, which requires Python>=3.7

The problem I had was that on my linux machine, the python3 command points to Python 3.6 which is not supported by PyO3. I also found that the shell VSCode uses for rust-analyser did not use my .bashrc profile. The workaround was to add the following to VSCode's settings.json:

{
    "rust-analyzer.server.extraEnv": {
        "PYO3_CROSS_LIB_DIR": "/home/peter.buxton/.local/share/uv/python/cpython-3.13.2-linux-x86_64-gnu/lib"
    }
}

To find what PYO3_CROSS_LIB_DIR should be you can do:
python -c "import sysconfig; print(sysconfig.get_config_var('LIBDIR'))"

I know that this is an issues which is quite a specific to my set-up, but it did take several hours to fix. So perhaps this can help someone else out.

Thanks,
Peter

[lnicola]

We are not going to include in the documentation anything specific to Python or even crates like PyO3, that variable is documented in https://pyo3.rs/v0.24.2/building-and-distribution.html#cross-compiling. Python 3.6 is EOL since 2021 and we wouldn't do anything for it anyway.

We do have a warning about environment variables here (for PATH), but that's very platform-specific: on Windows there's an UI for setting variables, Linux has /etc/environment, ~/.pam_environment and ~/.config/environment.d, but they don't work on every setup (and most Linux users don't seem to know about them), and MacOS IIRC has no way to set them at all.