override_settings doesn't send the setting_changed signal when restoring the original value

[Aymeric Augustin]

Django 1.4 introduces the override_settings context manager / decorator. When a setting is overridden, it fires the setting_changed signal. This signal allows to clean up or reset state that depends on a given setting, when that setting is changed.

However, in the current implementation, the signal isn't fired when the original value of the setting is restored.

I think setting_changed would be easier to use if it's fired whenever the value of a setting is "changed" in a broad sense, that is "overridden" or "reset".

While discussing this on IRC, it was suggested to add an extra argument, like state="pre" / "post", to distinguish between the two phases.

I'm marking this ticket as a release blocker because it would significantly change the behavior of setting_changed; we must make a decision before 1.4.

It's also a prerequisite for 17882-second-take.patch on #17882.

Patch w/ tests and docs attached.

[Claude Paroz]

I'm not super-convinced of the state argument. Would be nice to have a use case for it, even hypothetical.

[Aymeric Augustin]

In [17708]:

Fixed #17895 -- Made override_settings send the setting_changed signal both when a setting is overridden and when it's restored.