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
28577	Create system checks for mutable defaults on ArrayField and JSONField	Flávio Juvenal	Flávio Juvenal	"Django docs state ""Incorrectly using default=[] creates a mutable default that is shared between all instances of ArrayField."" [1].
This is a subtle bug that can be prevented with a new system check. IMO error prevention is good UX. Django should have system checks for those warnings in docs.
I've implemented this check: https://github.com/django/django/pull/8930

[1] https://docs.djangoproject.com/en/1.11/ref/contrib/postgres/fields/#django.contrib.postgres.fields.ArrayField"	New feature	closed	Core (System checks)	dev	Normal	fixed	check		Accepted	1	0	0	1	0	0