Should pip support named local requirements?

[sbidoul]

Pip cannot install packages from relative local directories that depend on each other.

Assume you have toola/setup.py:

from setuptools import setup

setup(
    name="toola",
    install_requires=["toolb"],
)

and toolb/setup.py

from setuptools import setup

setup(
    name="toolb",
)

So toola depends on toolb.

pip install --no-index ./toola ./toolb fails with No matching distribution found for toolb (from toola==0.0.0).

A workaround is to use PEP 508 direct urls, so this works:

pip install --no-index "toola @ file://$PWD/toola" "toolb @ file://$PWD/toolb"

Note PEP 508 requires absolute paths. This is however inconvenient and it is not possible to put this in a requirement file.

Describe the solution you'd like

It seems the issue stems from limitation of dependency resolution in presence of unnamed requirements.

PEP 508 provides a mechanism to name requirements, but rightly forbids relative file:// URLs with relative paths. This should continue to be forbidden in Requires-Dist metadata (see discussion).

So I see two approaches:

1. allow a syntax "name @ localdirectory(/localarchive)" for top level requirements only, to help the resolver
2. improve the resolution algorithm to extract metadata earlier and discover the name of all top level requirement

Additional context

#192 also touches this subject.

[uranusjr]

pip install --no-index ./toola ./toolb fails with No matching distribution found for toolb (from toola==0.0.0).

I wonder if this should be attributed to the resolver’s incompetency. Ideally the resolver probably should be smart enough to know that ./toolb introduces toolb (by building it and introspecting metadata), without the user needing to supply that information.

[pfmoore]

The new resolver may address this (as we "prepare" unnamed requirements eagerly). Does this still happen f you use master with --unstable-feature=resolver?

[sbidoul]

Ah, yes indeed, the new resolver copes with that example just fine. Great!

So the remaining use case for named local requirements would be #192 (comment)