Allow for specifying local wheels and sdists as dependencies

[mdboom]

It is useful, especially when creating custom versions of dependencies that are compatible with CPython main, to specify local file paths as dependencies. Unfortunately, that's blocked by a feature that treats any dependency that matches a file path as a requirements file. This makes that check a little more specific which allows for installing wheels.

This feels like the "safe" backward compatible change, but to be honest, I don't know why this feature exists in the first place -- it doesn't seem to be documented and the unit tests don't fail when you remove this whole if clause. I would also be ok with just removing this if clause if preferred.

[kumaraditya303]

LGTM, Could you add a test for this? I think a simple test with mock would suffice. Thanks!

[ericsnowcurrently]

For the most part this seems good. There is basically just one thing that's throwing me off.

[ericsnowcurrently]

LGTM

[mdboom]

Had to go back to the drawing board on this approach, since install_requirements doesn't actually have any context to know the directory of the requirements.txt file. I instead moved the resolving to a full path to _add_from_file which parses the requirements.txt file.

[ericsnowcurrently]

LGTM

(and thanks for adding good tests)