Description

Even if a parameter is deprecated, a value passed to it must be preserved during the deprecation cycle! Othwerwise, we effectively remove the deprecated behavior before the cycle is complete.

This is only relevant if there's no replacement for the deprecated parameter. In that case, the given value preserved and passed to the replacing parameter, and the deprecated one can be overwritten with DEPRECATED.

E.g.

from skimage._shared.utils import deprecate_parameter, DEPRECATED

@deprecate_parameter("a", start_version="X", stop_version="X+2")
def foo(a=DEPRECATED):
    if a is True:
        print("Can still use deprecated behavior!")

foo(True)

should warn and print but only warns on main because it silently replaces with DEPRECATED.

Thankfully, it doesn't look like we are currently using the decorator in a way that is affected by this bug. Discovered while preparing #7353.

Checklist

• A descriptive but concise pull request title
• Docstrings for all functions
• Unit tests
• A gallery example in ./doc/examples for new features
• Contribution guide is followed

Release note

For maintainers and optionally contributors, please refer to the instructions on how to document this PR for the release notes.

During deprecation cycles, preserve the value of deprecated parameters
that don't have a new parameter as a replacement.