Support lock dependencies with lowest solvable versions

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Feature Request

Context

When I am implementing a library, it would be super useful to run my tests with all the supported dependencies defined with the constrains in pyproject.toml. This will prevent errors in production when, for example, I use some new features of a dependency and forget to update the dependencies constrains (this is hard to identify when you are coding).

Because running the tests with all the possible combinations of all your supported libraries is virtually impossible, maybe running them with the lowest versions solvable solution and also the highest (I think this is the default behavior)

Proposal

• add the flag --use-lowest-versions to the cli entrypoints (install, sync, lock, shell, and run)
• these commands will create and/or use a different lock file poetry.lowest.lock
• a different venv will be created by just adding lowest after the project name like this: {project_name}-lowest-{id}-{python-version}

Main simple use case

In ci do the following steps

• Install environments

>>> poetry install 
>>> poetry install --use-lowest-versions

• run tests for highest versions

poetry run pytest  --junit-xml pytest.xml

• run tests for lowest versions

poetry run --use-lowest-versions pytest  --junit-xml pytest.xml

Note: I would appreciate if anyone has a better name for the flag (naming is the hardest part 😛)

Also, I looked a the code and I think I know where add this logic, I can create a PR if you like the idea

[Spectre5]

Ya, I don’t understand how library authors are not clamoring for this. If you put a minimum version in your dependency, it makes 100% sense to test with that version in case you accidentally use a feature from a newer version of it. Then you can decide to bump the dependency version or re-work your code to maintain that older compatibility. I’ve seen this happen on multiple projects and each would have been saved by testing against the minimum version dependencies.

[davegaeddert]

I went off of @JorgeGarciaIrazabal’s comment and played with here if anyone is curious: https://github.com/davegaeddert/poetry/pull/1

Very rough stab and I’m sure there’s all kinds of quirks that could come out of it. But, it was enough for me to poke around some of my own packages and do poetry upgrade --min-versions and then run my tests, and realize there’s usually a problem with the min requirements.