[BUG] certain editable installs allow case-insensitive imports

[aganders3]

setuptools version

setuptools==68.0.0

Python version

Python 3.10.12

OS

macOS

Additional environment information

I believe this is only a problem on macOS because of its case-preserving but case-insensitive filesytem. I'm not too familiar with filesystems but it may be a problem on others. See also PEP 235 - Import on Case-Insensitive Platforms.

I think this also depends on exactly how it is installed, but I'm not familiar with what determines which editable installation method is used.

Description

I have a project with the following structure:

├── pyproject.toml
├── setup.cfg
└── setuptools_editable_case_insensitive
    ├── __init__.py
    └── module_1.py

When the package is installed as editable, I am able to import module_1 with arbitrary case:

>>> from setuptools_editable_case_insensitive import module_1
>>> from setuptools_editable_case_insensitive import MODULE_1
>>> import setuptools_editable_case_insensitive.Module_1

Expected behavior

I expected to get an ImportError when importing a module with incorrect case, as is the behavior when installed normally:

>>> from setuptools_editable_case_insensitive import Module_1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name 'Module_1' from 'setuptools_editable_case_insensitive' (/Users/aandersoniii/src/setuptools-example/setuptools_editable_case_insensitive/__init__.py)

How to Reproduce

1. Clone this simplified example: git clone git@github.com:aganders3/setuptools-editable-case-insensitive.git
2. Create a virtual environment: cd setuptools-editable-case-insensitive && python3.10 -m venv venv && source venv/bin/activate
3. Install the project as editable: pip install -e .
4. Run the test script: python test_imports.py
5. Note module_1 is successfully imported with arbitrary case

Output

❯ git clone git@github.com:aganders3/setuptools-editable-case-insensitive.git
Cloning into 'setuptools-editable-case-insensitive'...
remote: Enumerating objects: 7, done.
remote: Counting objects: 100% (7/7), done.
remote: Compressing objects: 100% (6/6), done.
remote: Total 7 (delta 0), reused 7 (delta 0), pack-reused 0
Receiving objects: 100% (7/7), done.

❯ cd setuptools-editable-case-insensitive && python3.10 -m venv venv && source venv/bin/activate

❯ pip install -e .
Obtaining file:///Users/aandersoniii/src/setuptools-editable-case-insensitive
  Installing build dependencies ... done
  Checking if build backend supports build_editable ... done
  Getting requirements to build editable ... done
  Installing backend dependencies ... done
  Preparing editable metadata (pyproject.toml) ... done
Building wheels for collected packages: setuptools-editable-case-insensitive
  Building editable for setuptools-editable-case-insensitive (pyproject.toml) ... done
  Created wheel for setuptools-editable-case-insensitive: filename=setuptools_editable_case_insensitive-0.0.0-0.editable-py3-none-any.whl size=2787 sha256=580be31a2260f44e9e877f905ac5875526d31d0f46a433eb72b9103b55f7cb31
  Stored in directory: /private/var/folders/dd/w2cggkp91dq_xn53d6fphp8c0000gq/T/pip-ephem-wheel-cache-ik0hfo9g/wheels/a7/9d/6e/26a7dd6200d0678dcfb12a1d9447413c2a95d67d6a00fefc74
Successfully built setuptools-editable-case-insensitive
Installing collected packages: setuptools-editable-case-insensitive
Successfully installed setuptools-editable-case-insensitive-0.0.0

❯ python test_imports.py 
Hello from setuptools_editable_case_insensitive.module_1!
Hooray, I was imported with the correct name!
	__name__='setuptools_editable_case_insensitive.module_1'
	__file__='/Users/aandersoniii/src/setuptools-editable-case-insensitive/setuptools_editable_case_insensitive/module_1.py'

Hello from setuptools_editable_case_insensitive.Module_1!
Oh no, I was imported with the wrong name!
	__name__='setuptools_editable_case_insensitive.Module_1'
	__file__='/Users/aandersoniii/src/setuptools-editable-case-insensitive/setuptools_editable_case_insensitive/Module_1.py'

[aganders3]

This seems to be a problem when using the _EditableFinder. I can open a PR with a potential fix if it is welcome.

[abravalheri]

Hi @aganders3 a PR would be very useful, thank you for working on that.

For the finder we use pathlib.Path.exists and importlib.utils.spec_from_file_location. Do you know if these functions also suffer from the same problem?

[aganders3]

Yes, that's basically the problem. pathlib.Path.exists will return True even with the wrong case on macOS. Likewise spec_from_file_location will return a spec.

My proposed fix is in #3995 but feedback is appreciated. I am curious if a similar fix would be needed for namespace packages, but I don't know too much about them.