Allow stubs-only mixed project layout

[messense]

Fixes #792

Note that this only allows it to build, it doesn't re-export the Rust module to top module level as in

maturin/src/module_writer.rs

Lines 646 to 658 in 4f92d4d

	// Reexport the shared library as if it were the top level module
	writer.add_bytes(
	&module.join("__init__.py"),
	format!(
	r#"from .{module_name} import *
	__doc__ = {module_name}.__doc__
	if hasattr({module_name}, "__all__"):
	__all__ = {module_name}.__all__"#,
	module_name = module_name
	)
	.as_bytes(),
	)?;

@kevinheavey I'd love to know more about your requirements.

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[kevinheavey]

@kevinheavey I'd love to know more about your requirements.

So for my use case, I just want to mimic the standard experience of a Python project with multiple submodules (from mypackage.module_a import foo, from mypackage.module_b import bar. This is just because I'm working on something where the namespace will get very polluted otherwise.

it doesn't re-export the Rust module to top module level

I don't understand what this entails. I'm guessing it means there's something that I can't do if I use this approach?

[kevinheavey]

So how does one import the package then?

[messense]

So how does one import the package then?

Never mind, I think that's a problem with my IPython setup, using python3 works.

[kevinheavey]

Nice, and with this approach, do things like maturin develop and maturin publish "just work"? And everything gets uploaded to PyPI in one package?

[messense]

I think it should, note that you need to add a py.typed file to python module folder to actually enable type hints.

[kevinheavey]

Sounds awsome! The last thing I'm curious about is why we're referring to a mixed project layout. In my head this is just a pure Rust layout but with a directory of stub files instead of a single one

[messense]

Using a mixed project layout is the simplest solution, and we actually generate a mixed project layout for pure Rust project internally anyway. (See #558)