[1.11.x] Fixed #25192 -- Fixed squashmigrations crash with RunPython.noop on Python 2.

Thanks Adam Johnson for review.

django/db/migrations/operations/special.py

@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 from django.db import router
+from django.utils import six
 
 from .base import Operation
 
@@ -203,3 +204,11 @@ class RunPython(Operation):
     @staticmethod
     def noop(apps, schema_editor):
         return None
+
+
+# Allow migrations using RunPython.noop to be squashed on Python 2 (it doesn't
+# support serializating unbound method so install a module function instead).
+if six.PY2:
+    def noop(apps, schema_editor):
+        return None
+    RunPython.noop = staticmethod(noop)

tests/migrations/test_commands.py

@@ -1392,3 +1392,7 @@ class SquashMigrationsTests(MigrationTestBase):
             )
             with self.assertRaisesMessage(CommandError, msg):
                 call_command("squashmigrations", "migrations", "0003", "0002", interactive=False, verbosity=0)
+
+    def test_squashmigrations_squashes_noop(self):
+        with self.temporary_migration_module(module="migrations.test_migrations_squash_noop"):
+            call_command("squashmigrations", "migrations", "0002", interactive=False, verbosity=0)

tests/migrations/test_migrations_squash_noop/0001_initial.py

@@ -0,0 +1,11 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    operations = []

tests/migrations/test_migrations_squash_noop/0002_second.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+def dummy_python_op(apps, schema_editor):
+    return None
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("migrations", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.RunPython(dummy_python_op, migrations.RunPython.noop, elidable=False),
+    ]