Fixed #29180 -- Fixed a regression where migrations already in the plan were readded.

Regression in a38ae914d8.

django/db/migrations/graph.py

@@ -356,7 +356,7 @@ class MigrationGraph:
         plan = []
         for node in nodes:
             for migration in self.forwards_plan(node):
-                if migration in plan or at_end or migration not in nodes:
+                if migration not in plan and (at_end or migration not in nodes):
                     plan.append(migration)
         return plan
 

tests/migrations/test_loader.py

@@ -81,6 +81,22 @@ class LoaderTests(TestCase):
         # Ensure we've included unmigrated apps in there too
         self.assertIn("basic", project_state.real_apps)
 
+    @override_settings(MIGRATION_MODULES={
+        'migrations': 'migrations.test_migrations',
+        'migrations2': 'migrations2.test_migrations_2',
+    })
+    @modify_settings(INSTALLED_APPS={'append': 'migrations2'})
+    def test_plan_handles_repeated_migrations(self):
+        """
+        _generate_plan() doesn't readd migrations already in the plan (#29180).
+        """
+        migration_loader = MigrationLoader(connection)
+        nodes = [('migrations', '0002_second'), ('migrations2', '0001_initial')]
+        self.assertEqual(
+            migration_loader.graph._generate_plan(nodes, at_end=True),
+            [('migrations', '0001_initial'), ('migrations', '0002_second'), ('migrations2', '0001_initial')]
+        )
+
     @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_unmigdep"})
     def test_load_unmigrated_dependency(self):
         """