"markers" don't respect "target Python" configuration

[mitchhentges]

Description

I would like to download all the packages listed in a requirements file using a specific python version. However, the --python-version value isn't respected by marker evaluation.

Expected behavior

I think that pip should use specific configuration --python-version, --implementation, etc when resolving environment markers.
So, when the specified requirements.txt is used with pip download ... --python-version 3.6.15, it should download idna==2.10

pip version

22.0.4

Python version

3.9.12

OS

macOS Monterey 12.3 M1

How to Reproduce

1. Create a requirements file with the following contents:

idna==2.10; python_version < "3.7"

2. Run pip download -r requirements.txt --no-deps --dest . --abi none --platform any --python-version 3.6.15
3. pip outputs the following:

Ignoring idna: markers 'python_version < "3.7"' don't match your environment

Output

(poetry-env) mhentges@mhentges-39603 poetry-project % cat requirements.txt 
idna==2.10; python_version < "3.7"
(poetry-env) mhentges@mhentges-39603 poetry-project % pip download -r requirements.txt --no-deps --dest . --abi none --platform any --python-version 3.6.15
Ignoring idna: markers 'python_version < "3.7"' don't match your environment

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[mitchhentges]

Additional details:

• I think the problem area is roughly here, where the target_python from earlier should perhaps be reused

[uranusjr]

Duplicate of #10050.