Issue

We use constrain_package_deps = true and to our surprise, our dependencies that are in our constraints.txt that start with the letter c, that letter gets removed.

Environment

Provide at least:

• OS: linux

Minimal example

Use these files to reproduce it:

[tox]
min_version = 4.14.1
envlist =
    test

[testenv:test]
allowlist_externals = echo
skip_install = true
constrain_package_deps = true
deps =
    zope.interface
    -c constraints.txt
commands =
    echo 1

Download locally: https://dist.plone.org/release/6.0.7/requirements.txt

wget https://dist.plone.org/release/6.0.7/requirements.txt

And run tox:

tox -e test

After tox fails (on purpose), look at the generated .tox/test/constraints.txt and you will see that there is no collective.XXX version pins but rather ollective.XXX version pins.