Maturin breaks when you have a directory of stub files instead of a single stub file

[kevinheavey]

Bug Description

When you run maturin develop on a pure Rust project containing a directory of stub files, you get the error message Found a directory with the module name (solders) next to Cargo.toml, which indicates a mixed python/rust project, but the directory didn't contain an __init__.py file.

From looking at the maturin code, it looks like it thinks you have a mixed python/rust project when it sees a subdirectory with the same name as the library. If you change the stubs directory name then the type hints don't actually work.

Your Python version (python -V)

Python 3.9

Your pip version (pip -V)

21.2.4

What bindings you're using

No response

Does cargo build work?

• Yes, it works

If on windows, have you checked that you aren't accidentally using unix path (those with the forward slash /)?

• Yes

Steps to Reproduce

I've made an example repo here https://github.com/kevinheavey/maturin-stub-package-error

This is what I did:

1. Create a new project with maturin init.
2. Make a directory of stub files where the directory name matches the library name.
3. Run maturin develop and get the error Found a directory with the module name (solders) next to Cargo.toml, which indicates a mixed python/rust project, but the directory didn't contain an __init__.py file.

[messense]

Maturin doesn't support pure stub packages right now, so labelling this as a feature request.

[messense]

I think stub only package from PEP 561 is suitable for this? That is you provide a maturin-stub-package-error-stubs package for maturin-stub-package-error.

[kevinheavey]

I think stub only package from PEP 561 is suitable for this? That is you provide a maturin-stub-package-error-stubs package for maturin-stub-package-error.

Does this mean the stub package gets published as a separate package on PyPI?

[messense]

Does this mean the stub package gets published as a separate package on PyPI?

Yes, it needs to be published separately.