Prioritize EditableFinder over PathFinder in meta_path

[Naikless]

The current template for the addition of the EditableFinder for a package installed by pip install -e path/to/mypackage appends it to sys.meta_path:

setuptools/setuptools/command/editable_wheel.py

Line 890 in 5a13876

sys.meta_path.append(_EditableFinder)

This means that it gets imported only when no package of the same name can be found using the PathFinder, which for instance looks into site_packages. Normally, this poses no problem, because the pip install command uninstalls any package of the same name before doing the editable install.

However, "expanding" the local site-packages directory by using (additional) .pth files, packages found in these additional locations will always shadow editable installs, because pip can't touch them.

Example:

I have a rather large venv, let's call it base_env. I want to make modifications to it (update/remove some packages) and would like to test this.

I could create an empty second venv (test_env) and just add a .pth file to its site-packages directory that points to the base_env's site-packages. This way, I have access to all of base_env's packages in test_env. If I update any of them using pip install -U mypackage, pip will install the new version in test_env's site-packages dir, try to uninstall the old version and fail. But that's ok, because the local site-packages dir takes precedence over the one in base_env due to the order in sys.path, so when importing mypackage, I'll get the local, updated version.

The same happens when I just do a regular install from local source files by doing pip install path/to/mypackage.

However, when I execute pip install -e path/to/mypackage, import mypackage will always give me the version from base_env, because the EditableFinder is never called since the package was already found by the PathFinder.

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I realize this might be an edge case, but I don't find the scenario all too contrived and the fact that just adding -e to the pip command in this case completely changes import behavior at least violates POLA to me.

Would there be a downside to ensuring that editable installs always take precedence over potentially existing packages of the same name? This could be achieved by simply changing the position in sys.meta_path.