REQUESTED not created when a top level requirement is constrained

[sbidoul]

Description

When installing pip generates a REQUESTED metadata file for top level requirements.

However when such a top level requirements is constrained via -c, the REQUESTED file is not produced.

Expected behavior

No response

pip version

main, today, as well as 22.0.4

Python version

not relevant

OS

not relevant

How to Reproduce

Assume the following requirements.txt.in

pip-test-package @ git+https://github.com/pypa/pip-test-package@0.1.1

Now install pip-test-package with pip install -c requirements.txt.in pip-test-package.

Notice REQUESTED is not generated in site-packages/pip_test_package-0.1.1.dist-info/

It should be since pip-test-package is a top level requirement.

Output

No response

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[sbidoul]

I noticed that while working on #10771 where I want to use the InstallRequirement.user_supplied flag to produce a requested field in the report.