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