[1.8.x] Refs #24264 -- Added failing test case for updating a FK when changing a PK

When the primary key column is altered, foreign keys of referencing
models must be aware of a possible data type change as well and thus
need to be re-rendered.

Thanks Tim Graham for the report.

Backport of cc22b009e0 from master

tests/migrations/migrations_test_apps/alter_fk/author_app/migrations/0001_initial.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Author',
+            fields=[
+                ('id', models.AutoField(serialize=False, auto_created=True, primary_key=True)),
+                ('name', models.CharField(max_length=50)),
+            ],
+        ),
+    ]

tests/migrations/migrations_test_apps/alter_fk/author_app/migrations/0002_alter_id.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('author_app', '0001_initial'),
+        ('book_app', '0001_initial'),  # Forces the book table to alter the FK
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='author',
+            name='id',
+            field=models.CharField(max_length=10, primary_key=True),
+        ),
+    ]

tests/migrations/migrations_test_apps/alter_fk/book_app/migrations/0001_initial.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('author_app', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Book',
+            fields=[
+                ('id', models.AutoField(serialize=False, auto_created=True, primary_key=True)),
+                ('title', models.CharField(max_length=50)),
+                ('author', models.ForeignKey('author_app.Author')),
+            ],
+        ),
+    ]

tests/migrations/test_executor.py

@@ -376,6 +376,41 @@ class ExecutorTests(MigrationTestBase):
         ]
         self.assertEqual(call_args_list, expected)
 
+    @override_settings(
+        INSTALLED_APPS=[
+            "migrations.migrations_test_apps.alter_fk.author_app",
+            "migrations.migrations_test_apps.alter_fk.book_app",
+        ]
+    )
+    def test_alter_id_type_with_fk(self):
+        try:
+            executor = MigrationExecutor(connection)
+            self.assertTableNotExists("author_app_author")
+            self.assertTableNotExists("book_app_book")
+            # Apply initial migrations
+            executor.migrate([
+                ("author_app", "0001_initial"),
+                ("book_app", "0001_initial"),
+            ])
+            self.assertTableExists("author_app_author")
+            self.assertTableExists("book_app_book")
+            # Rebuild the graph to reflect the new DB state
+            executor.loader.build_graph()
+
+            # Apply PK type alteration
+            executor.migrate([("author_app", "0002_alter_id")])
+
+            # Rebuild the graph to reflect the new DB state
+            executor.loader.build_graph()
+        finally:
+            # We can't simply unapply the migrations here because there is no
+            # implicit cast from VARCHAR to INT on the database level.
+            with connection.schema_editor() as editor:
+                editor.execute(editor.sql_delete_table % {"table": "book_app_book"})
+                editor.execute(editor.sql_delete_table % {"table": "author_app_author"})
+            self.assertTableNotExists("author_app_author")
+            self.assertTableNotExists("book_app_book")
+
 
 class FakeLoader(object):
     def __init__(self, graph, applied):