`pip-sync --python-executable` evaluates markers for the wrong environment

[gschaffner]

pip-sync --python-executable evaluates environment markers for the wrong environment. It evaluates for the calling environment instead of the target environment.

Environment Versions

1. OS Type: Arch Linux
2. Python version: multiple required to repro; see below
3. pip version: 24.1.2
4. pip-tools version: 7.4.1

Steps to replicate

Minimal reproducer:

#!/usr/bin/env bash

shopt -s inherit_errexit
set -o errexit -o errtrace -o nounset -o pipefail -o xtrace

cd "$(mktemp -d)"

:
python3.12 -m venv --upgrade-deps .venv312
.venv312/bin/python -V
.venv312/bin/pip install --quiet pip-tools
.venv312/bin/pip-sync --version
.venv312/bin/pip --version

:
python3.11 -m venv --upgrade-deps .venv311
.venv311/bin/python -V
.venv311/bin/pip uninstall --quiet --yes setuptools
.venv311/bin/pip --version

:
<<EOF cat > req.pipreq
typing-extensions==4.12.2 ; python_version < "3.12"
EOF
.venv312/bin/pip-sync --python-executable=.venv311/bin/python req.pipreq
.venv311/bin/python -c 'import typing_extensions'

Output:

++ mktemp -d
+ cd /tmp/tmp.0EtEvbDhIl
+ :
+ python3.12 -m venv --upgrade-deps .venv312
+ .venv312/bin/python -V
Python 3.12.4
+ .venv312/bin/pip install --quiet pip-tools
+ .venv312/bin/pip-sync --version
pip-sync, version 7.4.1
+ .venv312/bin/pip --version
pip 24.1.2 from /tmp/tmp.0EtEvbDhIl/.venv312/lib/python3.12/site-packages/pip (python 3.12)
+ :
+ python3.11 -m venv --upgrade-deps .venv311
+ .venv311/bin/python -V
Python 3.11.9
+ .venv311/bin/pip uninstall --quiet --yes setuptools
+ .venv311/bin/pip --version
pip 24.1.2 from /tmp/tmp.0EtEvbDhIl/.venv311/lib/python3.11/site-packages/pip (python 3.11)
+ :
+ cat
+ .venv312/bin/pip-sync --python-executable=.venv311/bin/python req.pipreq
Everything up-to-date
+ .venv311/bin/python -c 'import typing_extensions'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ModuleNotFoundError: No module named 'typing_extensions'

Expected result

pip-sync installs typing_extensions.

Actual result

pip-sync exits 0 without installing typing_extensions (Everything up-to-date).