[1.10.x] Fixed #27100 -- Included already applied migration changes in the pre-migrate state.

Refs #24100.

Thanks Tim for the review.

Backport of d5c4ea524679a787fe11c927448e44e95646096b from master

4 files changed, 42 insertions, 30 deletions

diff --git a/django/core/management/commands/migrate.py b/django/core/management/commands/migrate.py
index 4c8e008374..6846b33d2a 100644
--- a/django/core/management/commands/migrate.py
+++ b/django/core/management/commands/migrate.py
@@ -160,7 +160,8 @@ class Command(BaseCommand):
                         % (targets[0][1], targets[0][0])
                     )
 
-        pre_migrate_apps = executor._create_project_state().apps
+        pre_migrate_state = executor._create_project_state(with_applied_migrations=True)
+        pre_migrate_apps = pre_migrate_state.apps
         emit_pre_migrate_signal(
             self.verbosity, self.interactive, connection.alias, apps=pre_migrate_apps, plan=plan,
         )
@@ -198,10 +199,11 @@ class Command(BaseCommand):
         else:
             fake = options['fake']
             fake_initial = options['fake_initial']
-        post_migrate_project_state = executor.migrate(
-            targets, plan, fake=fake, fake_initial=fake_initial
+        post_migrate_state = executor.migrate(
+            targets, plan=plan, state=pre_migrate_state.clone(), fake=fake,
+            fake_initial=fake_initial,
         )
-        post_migrate_apps = post_migrate_project_state.apps
+        post_migrate_apps = post_migrate_state.apps
 
         # Re-render models of real apps to include relationships now that
         # we've got a final state. This wouldn't be necessary if real apps
diff --git a/django/db/migrations/executor.py b/django/db/migrations/executor.py
index 11a96ec81b..1a0b6f6322 100644
--- a/django/db/migrations/executor.py
+++ b/django/db/migrations/executor.py
@@ -63,10 +63,25 @@ class MigrationExecutor(object):
                         applied.add(migration)
         return plan
 
-    def _create_project_state(self):
-        return ProjectState(real_apps=list(self.loader.unmigrated_apps))
+    def _create_project_state(self, with_applied_migrations=False):
+        """
+        Create a project state including all the applications without
+        migrations and applied migrations if with_applied_migrations=True.
+        """
+        state = ProjectState(real_apps=list(self.loader.unmigrated_apps))
+        if with_applied_migrations:
+            # Create the forwards plan Django would follow on an empty database
+            full_plan = self.migration_plan(self.loader.graph.leaf_nodes(), clean_start=True)
+            applied_migrations = {
+                self.loader.graph.nodes[key] for key in self.loader.applied_migrations
+                if key in self.loader.graph.nodes
+            }
+            for migration, _ in full_plan:
+                if migration in applied_migrations:
+                    migration.mutate_state(state, preserve=False)
+        return state
 
-    def migrate(self, targets, plan=None, fake=False, fake_initial=False):
+    def migrate(self, targets, plan=None, state=None, fake=False, fake_initial=False):
         """
         Migrates the database up to the given targets.
 
@@ -82,15 +97,9 @@ class MigrationExecutor(object):
         all_backwards = all(backwards for mig, backwards in plan)
 
         if not plan:
-            # The resulting state should include applied migrations.
-            state = self._create_project_state()
-            applied_migrations = {
-                self.loader.graph.nodes[key] for key in self.loader.applied_migrations
-                if key in self.loader.graph.nodes
-            }
-            for migration, _ in full_plan:
-                if migration in applied_migrations:
-                    migration.mutate_state(state, preserve=False)
+            if state is None:
+                # The resulting state should include applied migrations.
+                state = self._create_project_state(with_applied_migrations=True)
         elif all_forwards == all_backwards:
             # This should only happen if there's a mixed plan
             raise InvalidMigrationPlan(
@@ -100,7 +109,10 @@ class MigrationExecutor(object):
                 plan
             )
         elif all_forwards:
-            state = self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
+            if state is None:
+                # The resulting state should still include applied migrations.
+                state = self._create_project_state(with_applied_migrations=True)
+            state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
         else:
             # No need to check for `elif all_backwards` here, as that condition
             # would always evaluate to true.
@@ -110,19 +122,14 @@ class MigrationExecutor(object):
 
         return state
 
-    def _migrate_all_forwards(self, plan, full_plan, fake, fake_initial):
+    def _migrate_all_forwards(self, state, plan, full_plan, fake, fake_initial):
         """
         Take a list of 2-tuples of the form (migration instance, False) and
         apply them in the order they occur in the full_plan.
         """
         migrations_to_run = {m[0] for m in plan}
-        state = self._create_project_state()
-        applied_migrations = {
-            self.loader.graph.nodes[key] for key in self.loader.applied_migrations
-            if key in self.loader.graph.nodes
-        }
         for migration, _ in full_plan:
-            if not migrations_to_run and not applied_migrations:
+            if not migrations_to_run:
                 # We remove every migration that we applied from these sets so
                 # that we can bail out once the last migration has been applied
                 # and don't always run until the very end of the migration
@@ -137,12 +144,6 @@ class MigrationExecutor(object):
                         self.progress_callback("render_success")
                 state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
                 migrations_to_run.remove(migration)
-            elif migration in applied_migrations:
-                # Only mutate the state if the migration is actually applied
-                # to make sure the resulting state doesn't include changes
-                # from unrelated migrations.
-                migration.mutate_state(state, preserve=False)
-                applied_migrations.remove(migration)
 
         return state
 
diff --git a/docs/releases/1.10.1.txt b/docs/releases/1.10.1.txt
index 46188aa2da..b5c72c5e8b 100644
--- a/docs/releases/1.10.1.txt
+++ b/docs/releases/1.10.1.txt
@@ -72,3 +72,7 @@ Bugfixes
 * Fixed the creation of ``ContentType`` and ``Permission`` objects for models
   of applications without migrations when calling the ``migrate`` command with
   no migrations to apply (:ticket:`27044`).
+
+* Included the already applied migration state changes in the ``Apps`` instance
+  provided to the ``pre_migrate`` signal receivers to allow ``ContentType``
+  renaming to be performed on model rename (:ticket:`27100`).
diff --git a/tests/migrate_signals/tests.py b/tests/migrate_signals/tests.py
index 777ee41efa..6d98e7246e 100644
--- a/tests/migrate_signals/tests.py
+++ b/tests/migrate_signals/tests.py
@@ -114,12 +114,17 @@ class MigrateSignalTests(TransactionTestCase):
             ['migrate_signals.Signal']
         )
         # Migrating with an empty plan.
+        pre_migrate_receiver = Receiver(signals.pre_migrate)
         post_migrate_receiver = Receiver(signals.post_migrate)
         management.call_command(
             'migrate', database=MIGRATE_DATABASE, verbosity=MIGRATE_VERBOSITY,
             interactive=MIGRATE_INTERACTIVE, stdout=stdout,
         )
         self.assertEqual(
+            [model._meta.label for model in pre_migrate_receiver.call_args['apps'].get_models()],
+            ['migrate_signals.Signal']
+        )
+        self.assertEqual(
             [model._meta.label for model in post_migrate_receiver.call_args['apps'].get_models()],
             ['migrate_signals.Signal']
         )