Fixed #29738 -- Allowed serializing psycopg2 range types in migrations.

django/contrib/postgres/apps.py

+from psycopg2.extras import (
+    DateRange, DateTimeRange, DateTimeTZRange, NumericRange,
+)
+
 from django.apps import AppConfig
 from django.db import connections
 from django.db.backends.signals import connection_created
+from django.db.migrations.writer import MigrationWriter
 from django.db.models import CharField, TextField
 from django.test.signals import setting_changed
 from django.utils.translation import gettext_lazy as _
 
 from .lookups import SearchLookup, TrigramSimilar, Unaccent
+from .serializers import RangeSerializer
 from .signals import register_type_handlers
 
+RANGE_TYPES = (DateRange, DateTimeRange, DateTimeTZRange, NumericRange)
+
 
 def uninstall_if_needed(setting, value, enter, **kwargs):
     """
@@ -26,6 +34,7 @@ def uninstall_if_needed(setting, value, enter, **kwargs):
         # and ready() connects it again to prevent unnecessary processing on
         # each setting change.
         setting_changed.disconnect(uninstall_if_needed)
+        MigrationWriter.unregister_serializer(RANGE_TYPES)
 
 
 class PostgresConfig(AppConfig):
@@ -54,3 +63,4 @@ class PostgresConfig(AppConfig):
         TextField.register_lookup(SearchLookup)
         CharField.register_lookup(TrigramSimilar)
         TextField.register_lookup(TrigramSimilar)
+        MigrationWriter.register_serializer(RANGE_TYPES, RangeSerializer)

django/contrib/postgres/serializers.py

+from django.db.migrations.serializer import BaseSerializer
+
+
+class RangeSerializer(BaseSerializer):
+    def serialize(self):
+        module = self.value.__class__.__module__
+        # Ranges are implemented in psycopg2._range but the public import
+        # location is psycopg2.extras.
+        module = 'psycopg2.extras' if module == 'psycopg2._range' else module
+        return '%s.%r' % (module, self.value), {'import %s' % module}

tests/postgres_tests/test_apps.py

 from django.db.backends.signals import connection_created
+from django.db.migrations.writer import MigrationWriter
 from django.test.utils import modify_settings
 
 from . import PostgreSQLTestCase
 
+try:
+    from psycopg2.extras import (
+        DateRange, DateTimeRange, DateTimeTZRange, NumericRange,
+    )
+    from django.contrib.postgres.fields import (
+        DateRangeField, DateTimeRangeField, IntegerRangeField,
+    )
+except ImportError:
+    pass
+
 
 class PostgresConfigTests(PostgreSQLTestCase):
     def test_register_type_handlers_connection(self):
@@ -11,3 +22,38 @@ class PostgresConfigTests(PostgreSQLTestCase):
         with modify_settings(INSTALLED_APPS={'append': 'django.contrib.postgres'}):
             self.assertIn(register_type_handlers, connection_created._live_receivers(None))
         self.assertNotIn(register_type_handlers, connection_created._live_receivers(None))
+
+    def test_register_serializer_for_migrations(self):
+        tests = (
+            (DateRange(empty=True), DateRangeField),
+            (DateTimeRange(empty=True), DateRangeField),
+            (DateTimeTZRange(None, None, '[]'), DateTimeRangeField),
+            (NumericRange(1, 10), IntegerRangeField),
+        )
+
+        def assertNotSerializable():
+            for default, test_field in tests:
+                with self.subTest(default=default):
+                    field = test_field(default=default)
+                    with self.assertRaisesMessage(ValueError, 'Cannot serialize: %s' % default.__class__.__name__):
+                        MigrationWriter.serialize(field)
+
+        assertNotSerializable()
+        with self.modify_settings(INSTALLED_APPS={'append': 'django.contrib.postgres'}):
+            for default, test_field in tests:
+                with self.subTest(default=default):
+                    field = test_field(default=default)
+                    serialized_field, imports = MigrationWriter.serialize(field)
+                    self.assertEqual(imports, {
+                        'import django.contrib.postgres.fields.ranges',
+                        'import psycopg2.extras',
+                    })
+                    self.assertIn(
+                        '%s.%s(default=psycopg2.extras.%r)' % (
+                            field.__module__,
+                            field.__class__.__name__,
+                            default,
+                        ),
+                        serialized_field
+                    )
+        assertNotSerializable()