Surprising behaviour (and missing warning?) with overlaping python versions

[DMRobertson]

• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

  • closest I could find was poetry selects wrong python version when markers present #4959 but there are no markers here; just using the python version syntax only.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Linux, Fedora 35

• Poetry version: $ poetry --version
  Poetry version 1.1.12

• Link of a Gist with the contents of your pyproject.toml file:

Issue

When experimenting with how poetry lock files handle different python versions, I tried poetry installing from the following pyproject.toml.

[tool.poetry]
name = "example-poetry"
version = "0.1.0"
description = ""
authors = ["David Robertson <david.m.robertson1@gmail.com>"]

[tool.poetry.dependencies]
python = "^3.10"

[tool.poetry.dev-dependencies]
pytest = "^5.2"
pillow = [
	{ version = "^9", python = "^3.9" },
	{ version = "^7", python = "^3.7" },
]

[build-system]
requires = ["poetry-core>=1.0.0"]
build-backend = "poetry.core.masonry.api"

I hadn't noticed that the project was scoped to python ^= 3.10. Running this on Python 3.10, I expected the constraing python ^3.9 to beat python ^3.7, and so expected poetry to select pillow ^9 at install time. What I saw instead was that poetry reported installing two copies of pillow:

$ poetry install
Creating virtualenv example-poetry-ZY5Szwk5-py3.10 in /home/dmr/.cache/pypoetry/virtualenvs
Updating dependencies
Resolving dependencies... (1.5s)

Writing lock file

Package operations: 10 installs, 0 updates, 0 removals

  • Installing pyparsing (3.0.6)
  • Installing attrs (21.4.0)
  • Installing more-itertools (8.12.0)
  • Installing packaging (21.3)
  • Installing pluggy (0.13.1)
  • Installing py (1.11.0)
  • Installing wcwidth (0.2.5)
  • Installing pillow (7.2.0)
  • Installing pillow (9.0.0)
  • Installing pytest (5.4.3)

Installing the current project: example-poetry (0.1.0)

The poetry 7.2.0 installation finished second (is this racey?). If I ask pillow what version is installed, it thinks 7.2:

$ poetry show pillow
name         : pillow
version      : 7.2.0
description  : Python Imaging Library (Fork)

If I ask pip, I get a different answer!!

 $ poetry run pip show pillow
Name: Pillow
Version: 9.0.0
Summary: Python Imaging Library (Fork)
Home-page: https://python-pillow.org
Author: Alex Clark (PIL Fork Author)
Author-email: aclark@python-pillow.org
License: HPND
Location: /home/dmr/.cache/pypoetry/virtualenvs/example-poetry-ZY5Szwk5-py3.10/lib64/python3.10/site-packages
Requires: 
Required-by: 

Confusingly, poetry show --tree includes both versions:

 $ poetry show --tree
pillow 7.2.0 Python Imaging Library (Fork)
pillow 9.0.0 Python Imaging Library (Fork)
pytest 5.4.3 pytest: simple powerful testing with Python
├── atomicwrites >=1.0
├── attrs >=17.4.0
├── colorama *
├── more-itertools >=4.0.0
├── packaging *
│   └── pyparsing >=2.0.2,<3.0.5 || >3.0.5 
├── pluggy >=0.12,<1.0
├── py >=1.5.0
└── wcwidth *

While I don't think I'm using poetry as intended, it'd be nice to avoid falling into this unusual situation is possible. Perhaps the tool could require that the python versions specified for a particular package are pairwise exclusive; i.e. that at most one rule applies to any given python version.

[github-actions]

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