Looks like we need to drop the importlib-resources upgrade https://github.com/python-poetry/poetry/pull/3905/files#diff-f53a023eedfa3fbf2925ec7dc76eecdc954ea94b7e47065393dbad519613dc89R376.

@abn It should not fail since markers are present and correct. I'll investigate but for now I will hold off the release.

@abn I think we are hitting a limit of the current resolver. And I don't see a simple solution to this issue.

I am surprised we did not hit this sooner but basically the issue comes from these two dependencies:

virtualenv = { version = "^20.0.26" }
pre-commit = { version = "^2.6", python = "^3.6.1" }

The resolver chooses to resolve pre-commit first: version 2.10.1 requires Python >= 3.6.1 and depends on importlib-resources (*) ; python_version < \"3.7\". That works for the resolver and it selects importlib-resources (5.1.2) which requires Python >= 3.6.

The resolver then resolves virtualenv which requires importlib-resources (>=1.0) ; python_version < \"3.7\". But the resolver in its current version assumes that importlib-resources (5.1.2) satisfies this constraint, which is only the case for Python >=3.6.1.

Well I may have a workaround it seems by prioritizing dependencies without markers first. This is not a silver bullet though and we might need to improve this part of the resolver.

IIUC, sounds almost like the resolver needs to keep the resolution context around from the previous result. In this case, knowing that importlib-resources (5.1.2) was resolved for >=3.6 should mean we resolve again for the difference right? This should essentially lead us to two different versions with mutually exclusive python version constraints.

@abn I tried something similar but that did not lead anywhere due to the way the resolver is structured, or it led to severe performance issues.

The workaround (#3944) should alleviate – and actually fix in most cases – the issue.

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