usedevelop without setup.py failure

[AntoineD]

When usedevelop is enabled with a project that only has a setup.cfg but no setup.py, on the second tox execution with no changes at all, tox crashes because VirtualEnv._needs_reinstall relies on setup.py to get the name of the project's package.

A PR is coming next.

[gaborbernat]

I don't think it's possible to use usedevelop without a setup.py. How does this even passes at first run?

[AntoineD]

I don't think it's possible to use usedevelop without a setup.py. How does this even passes at first run?

This happens with an env that does not run the tests, I'll see what happens otherwise.

[AntoineD]

This works fine when running pytest in the commands of the such an env.

@gaborbernat What do you mean by not possible?

[gaborbernat]

usedevelop implies the installation of the package via setup.py. The installation will fail without setup.py.

[AntoineD]

From what I can see, the installation works fine with only setup.cfg and no setup.py when usedevelop = True.

Have you tried?

[gaborbernat]

Hmm, did setuptools and pip change this? Can you dig up from pip+setuptools changelog when this was added? I know a while back you could not install in develop mode a package, because the interface was the setup.py file itself. It might work now but we need to figure out what versions of pip+setuptools require that 🤔

[AntoineD]

The failures of the PR's CI's jobs seems to be related to what you are saying. Things behave differently on my PC, I'll dig up.

[AntoineD]

This has been fixed in pip 21.1.

[posita]

Just curious, but what's the fix here? Tox should require pip>=21.1?

[AntoineD]

@posita Yes (not considering tox).

[posita]

A PR is coming next.

Is this still true, or should this be closed without a fix?

[AntoineD]

The PR has been closed without merge.

[posita]

I don't think pip fixes this. I still see this with pip==21.2.4.

Digging into this a bit, this works (including on the second and subsequent runs):

[tox]
# …
skipsdist = true

[testenv]
# …
deps =
    --editable .  # <-- this works

This fails on the second run (per the OP):

[tox]
# …
skipsdist = true

[testenv]
# …
usedevelop = True  # <-- this works once, then fails on subsequent runs