Support for package data

[nthiery]

Description

I have a Python package which includes package data, to be accessed
through importlib.resources. However, within jupyterlite, importlib.resources
fails do find the data.

Reproduce

1. Clone https://github.com/jupyterlite/xeus-python-demo

2. Add these dependencies to environment.yml

     - pip
     - pip:
       - "git+https://gitlab.dsi.universite-paris-saclay.fr/nicolas.thiery/Laby.git"
   

3. Build JupyterLite

   mamba env create --force -f build-environment.yml
   conda activate build-env
   cp README.md content
   jupyter lite build --contents content --output-dir dist
   

4. Check the log, and notice the copying of the package data when building the wheel:

   creating build/bdist.linux-x86_64/wheel/laby/resources/tiles_png
   copying build/lib/laby/resources/tiles_png/nweb.png -> build/bdist.linux-x86_64/wheel/laby/resources/tiles_png
   ...
   

5. Browse dist/extensions/@jupyterlite/xeus-python-kernel/static/laby_python-0.0.5-pip.tar.gz

   Expected behavior: the archive contain the package data.
   Got: the package contains only the Python code

6. Run JupyterLite and from a python kernel run:

   tiles_dir = importlib.resources.files("laby").joinpath("resources", "tiles_png")
   list(tiles_dir.glob("*"))
   

   Expected behavior: a list of files including 'nweb.png`.
   Got: the empty list

Context

• JupyterLite version: 0.1.2
• Operating System and version: Ubuntu 22.04
• Browser and version: Firefox/chromium

[martinRenou]

Thank you for opening an issue. Would you be able to confirm that os.path.exists("/lib/python3.10/site-packages/laby/resources/tiles_png/nweb.png") returns True?

I misread the issue. This will definitely return False if

Expected behavior: the archive contain the package data.
Got: the package contains only the Python code

So this has to do with either the empack filtering logic or the way we add package data for the pip dependencies. I'd bet on the empack filtering logic.