Locking dependencies fails when using python version constraints

• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Debian bookworm, Python 3.9.12, Python 3.7.13
• Poetry version: 1.2.0b2.dev0
• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/thueringa/a9fe9ea20408a5d1e54af4a8bd1eda58

Issue

I have the following dependencies:

[tool.poetry.dependencies]
python = "^3.7"
flake8 = "4.0.1"
sphinx = [
    {version = "4.3.1", python = "~3.7.0"},
    {version = "^4.5.0", python = "^3.8"},
]

Locking the depencies with poetry lock --no-update fails with the following error (see Gist for full output of poetry lock -vvv --no-update):

  SolverProblemError

  Because flake8 (4.0.1) depends on importlib-metadata (<4.3)
   and sphinx (4.5.0) depends on importlib-metadata (>=4.4), flake8 (4.0.1) is incompatible with sphinx (4.5.0).
  And because no versions of sphinx match >4.5.0,<5.0.0, flake8 (4.0.1) is incompatible with sphinx (>=4.5.0,<5.0.0).
  So, because poetry-test depends on both flake8 (4.0.1) and sphinx (^4.5.0), version solving failed.

  at ~/.local/lib/python3.10/site-packages/poetry/puzzle/solver.py:155 in _solve
      151│             packages = result.packages
      152│         except OverrideNeeded as e:
      153│             return self.solve_in_compatibility_mode(e.overrides, use_latest=use_latest)
      154│         except SolveFailure as e:
    → 155│             raise SolverProblemError(e)
      156│ 
      157│         combined_nodes = depth_first_search(PackageNode(self._package, packages))
      158│         results = dict(aggregate_package_nodes(nodes) for nodes in combined_nodes)
      159│ 

I would expect poetry to find a solution where flake8==4.0.1 is installed for all environments, sphinx==4.3.1 is installed for Python 3.7.* environments, and sphinx==4.5.0 is installed for all Python 3.8 environments and upwards.

A work-around is to define specific versions of flake8 for each Python environment:

[tool.poetry.dependencies]
python = "^3.7"
flake8 = [
    {version = "4.0.0", python = "~3.7.0"},
    {version = "4.0.1", python = "^3.8"},
]
sphinx = [
    {version = "4.3.1", python = "~3.7.0"},
    {version = "^4.5.0", python = "^3.8"},
]

This correctly locks the dependencies, but it only works when using different versions of flake8 for each kind of environment, which is impractical.

Additional information

Similar failing command

A similar set of dependencies that fails is this one:

[tool.poetry.dependencies]
python = "^3.7"
importlib-metadata = {version ="<4.3", python= "~3.7.0"}
sphinx = [
    {version = "4.3.1", python = "~3.7.0"},
    {version = "^4.5.0", python = "^3.8"},
]

I would expect poetry to find a solution for Python 3.8 environments and upwards that installs sphinx==4.5.0 and a compatible version of importlib-metadata that is defined in the dependencies of sphinx v4.5.0. For Python 3.7 environments I would expect poetry to find a solution that installs sphinx==4.3.1 and a version of importlib-metadata that adheres to our dependency constraint.

importlib-metadata dependencies in referenced packages flake8 and sphinx

The relevant lines concerning importlib-metadata in setup.cfg of flake8 v4.0.1 (unchanged from flake8 v4.0.0):

install_requires =
    [...]
    importlib-metadata<4.3;python_version<"3.8"

In setup.py of sphinx v4.5.0:

install_requires = [
    [...]
    "importlib-metadata>=4.4; python_version < '3.10'",
]

sphinx v4.3.1 does not seem to have a dependency on importlib-metadata.

Possibly related issues: #5506, #5447, #4695

[thueringa]

I should have thought about the set of dependencies diligently, I see now that this was an misunderstanding on my side on the dependencies of Sphinx v4.5.0. It does have a dependency on “importlib-metadata>=4.4; python_version < ‘3.10’”. So the behavior of Poetry in conjunction with Flake8 is correct, and the snippet in my opening post is not expected to be solvable.

Thank you for your help @Qu4tro, I will close this issue now.

[thueringa]

Sorry, yes, I got all the versions a bit mixed up in my head it seems… To clarify:

• flake8 depends on importlib-metadata<4.3;python_version<"3.8",
• sphinx v4.5.0 depends on "importlib-metadata>=4.4; python_version < '3.10'",
• sphinx v4.3.* has no dependency on importlib-metadata

So yes, I believe this is a regression bug of Poetry, as it should find a solution for this set of dependencies with the snippet above, like it did in v1.0.10.