Rust as an optional dependency

[LilyFoote]

I'm working on adding a rust extension to a python profiling tool to try and get a speed improvement. However, I'm relying on pyo3::ffi::PyEval_SetProfile, which is not available on PyPy.

Is there a recommended way to build wheels for CPython that include my rust extension (and my pure python code) and build wheels for PyPy that only include my pure python code?

[messense]

No support for making Rust extension optional, see #1081.

Sounds like you want https://docs.rs/pyo3-build-config/latest/pyo3_build_config/, for example

• https://github.com/pydantic/pydantic-core/blob/e146483e2becb6151e76539861db0053465bb22a/Cargo.toml#L64-L67
• https://github.com/pydantic/pydantic-core/blob/e146483e2becb6151e76539861db0053465bb22a/build.rs#L27

Then you can use #[cfg(not(PyPy))] in your code.

[LilyFoote]

Thanks! Once I put build.rs in the right place (not in src!) this worked great!