Cannot install pylock.toml from CPython dev version

[hugovk]

Description

CPython's dev versions don't strictly follow PEP 440 because of the plus: 3.15.0a8+

This prevents pip installing from a pylock.toml with this version.

Expected behavior

I expect to be able to install from a CPython dev version, because I'd like to use a lockfile for CPython's docs: python/cpython#149058.

pip version

25.1

Python version

3.15.0a8+

OS

macOS and Linux

How to Reproduce

1. Build CPython from source: https://devguide.python.org/
2. Save this as pylock.toml:

lock-version = "1.0"
created-by = "minimal-repro"
requires-python = ">=3.12"
packages = []

3. Install: python.exe -m pip install -r pylock.toml

Output

Defaulting to user installation because normal site-packages is not writeable
WARNING: Using pylock.toml as a requirements source is an experimental feature. It may be removed/changed in a future release without prior warning.
ERROR: Cannot select requirements from pylock file 'pylock.toml': python_full_version '3.15.0a8+' in provided environment does not satisfy the Python version requirement '>=3.12'

See also https://github.com/python/cpython/actions/runs/25007535303/job/73234353237?pr=149058

This comes from src/packaging/pylock.py

[hugovk]

Repro with just packaging:

from packaging.pylock import Pylock
from packaging.specifiers import SpecifierSet
from packaging.version import Version

pylock = Pylock(
  lock_version=Version("1.0"),
  created_by="repro",
  requires_python=SpecifierSet(">=3.12"),
  packages=[],
)
list(pylock.select(environment={"python_full_version": "3.15.0a8+"}))

Produces:

Traceback (most recent call last):
  File "<python-input-0>", line 11, in <module>
    list(pylock.select(environment={"python_full_version": "3.15.0a8+"}))
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/hugo/.local/lib/python3.15/site-packages/packaging/pylock.py", line 801, in select
    raise PylockSelectError(
    ...<3 lines>...
    )
packaging.pylock.PylockSelectError: python_full_version '3.15.0a8+' in provided environment does not satisfy the Python version requirement '>=3.12'

On latest main.

[sbidoul]

I see, we need to invoke a variant of _repair_python_full_version here:

packaging/src/packaging/pylock.py

Lines 785 to 789 in 9bfe549

	env_python_full_version = (
	environment["python_full_version"]
	if environment
	else default_environment()["python_full_version"]
	)

[sbidoul]

Proposed fix in #1179