From 1aadade373336c3f534986cdcc0ba33714d85c8e Mon Sep 17 00:00:00 2001
From: Baptiste Mispelon <bmispelon@gmail.com>
Date: Mon, 23 Mar 2015 15:38:25 +0100
Subject: [PATCH] Fixed #24521 -- Added support for serializing frozensets in
 migrations.

---
 django/db/migrations/writer.py  | 4 +++-
 tests/migrations/test_writer.py | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/django/db/migrations/writer.py b/django/db/migrations/writer.py
index 9067e7b605..f4f43ac930 100644
--- a/django/db/migrations/writer.py
+++ b/django/db/migrations/writer.py
@@ -302,7 +302,7 @@ class MigrationWriter(object):
             value = force_text(value)
 
         # Sequences
-        if isinstance(value, (list, set, tuple)):
+        if isinstance(value, (frozenset, list, set, tuple)):
             imports = set()
             strings = []
             for item in value:
@@ -312,6 +312,8 @@ class MigrationWriter(object):
             if isinstance(value, set):
                 # Don't use the literal "{%s}" as it doesn't support empty set
                 format = "set([%s])"
+            elif isinstance(value, frozenset):
+                format = "frozenset([%s])"
             elif isinstance(value, tuple):
                 # When len(value)==0, the empty tuple should be serialized as
                 # "()", not "(,)" because (,) is invalid Python syntax.
diff --git a/tests/migrations/test_writer.py b/tests/migrations/test_writer.py
index 28c68d871a..aa12c7c612 100644
--- a/tests/migrations/test_writer.py
+++ b/tests/migrations/test_writer.py
@@ -347,6 +347,10 @@ class WriterTests(TestCase):
         self.assertSerializedEqual(FoodManager('a', 'b'))
         self.assertSerializedEqual(FoodManager('x', 'y', c=3, d=4))
 
+    def test_serialize_frozensets(self):
+        self.assertSerializedEqual(frozenset())
+        self.assertSerializedEqual(frozenset("let it go"))
+
     def test_simple_migration(self):
         """
         Tests serializing a simple migration.