frozensets don't seem to work quite right in migrations as field kwargs

[ris]

Apologies if this is a rather sparse bug report, but I think it's quite a straightforward issue to explain.

Using django 1.7.7, a custom model field returning a frozenset as a value in the kwargs dict from deconstruct will cause makemigrations to seemingly coerce this value to a tuple. Because this tuple does not exactly equal the frozenset, this trips up makemigrations' change detection logic, and this will get detected as a "change" each and every time makemigrations is run for eternity.

Use of a set however works as expected, so this is a bit odd.

[Baptiste Mispelon]

PR here: ​https://github.com/django/django/pull/4387

[Baptiste Mispelon <bmispelon@…>]

In 1aadade:

Fixed #24521 -- Added support for serializing frozensets in migrations.