id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
21188	Use DeprecationWarning subclasses for deprecated features	Anssi Kääriäinen	nobody	"The idea is to introduce new deprecation subclass for each Django version. For example, in current master:
{{{
class ToBeRemovedInDjango19Warning(PendingDeprecationWarning):
    pass


class ToBeRemovedInDjango18Warning(DeprecationWarning):
    pass
}}}

By using these warnings we can achieve the following:
   - Moving PendingDeprecationWarning to DeprecationWarning after release is single line change.
   - It will be possible to filter on Django's deprecation warnings without catching warnings from non-django components.
   - It will be harder to miss removal of code. After 1.7 is released just remove ToBeRemovedInDjango18Warning. Any code importing that warning will immediately fail. Also, grepping might be a little easier.
   - After release, currently introducing a new PendingDeprecationWarning before PendingDeprecationWarnings are renamed to DeprecationWarnings (as part of release procedure) the new deprecatin will likely be moved to DeprecationWarning. But if a ToBeRemovedInDjango20Warning is added it will be really hard to accidentally move that one to DeprecationWarning.
   - It will be technically easy to provide for longer than two releases deprecation periods (if we ever want this).

Drawbacks:
   - If we use automatic filtering for deprecations, then code currently doing:
`warning.simplefilter(""always"", DeprecationWarning)`
     will no longer catch Django's deprecation warnings (as we added an entry for `warning.simplefilter(""default"" ToBeRemovedInDjango18Warning)` which matches before DeprecationWarning.

I tried this approach in: https://github.com/akaariai/django/compare/deprecation_subclasses#L3R18 - The patch is totally incomplete so I will not mark ""has patch""."	Cleanup/optimization	closed	Core (Other)	dev	Normal	fixed		adi@…	Ready for checkin	1	0	0	0	0	0