In the contributing guide document how to deprecate a feature

[Tim Graham]

Somewhere in internals/contributing we document guidelines for deprecating a feature. I couldn't find anything on this after a quick search.

This includes how to silence deprecation warnings:

When a feature is deprecated, it raises a PendingDeprecationWarning, either at import time or at run time. After the following release it raises DeprecationWarning. Assuming we have a good test coverage, these warnings will be shown by the test suite, with -Wall for PendingDeprecationWarning, or by default for DeprecationWarning. This is annoying. The output of the test suite should remain clean.

Aymeric's full post including how to silence warnings:
​https://groups.google.com/forum/#!topic/django-developers/nXlNqpy6sC8

[Aymeric Augustin]

#21025 was a duplicate.

[Marc Tamlyn]

Worth mentioning that we should make sure to take care when silencing deprecation warnings - eating our own dogfood must be the first step to removing the warnings.

[Keith Edmiston]

I think I may have found the location in the docs to be in the Minor Releases section of the ​Release Process page.

[Ivan Kolodyazhny]

"The first step is to remove any use of the deprecated behavior by Django itself"
What's about cases when some code doesn't used by Django itself?

[Tim Graham]

I'm not sure how common that would be. I guess I would handle that on a case by case basis.

[Tim Graham <timograham@…>]

In 5be56d0e0d8492a41b3d40757a4f2677211a9179:

Fixed #21024 -- Documented how to deprecate a feature.