Fixed #24870 -- Added --update option to makemigrations command.

4 files changed, 217 insertions, 2 deletions

diff --git a/django/core/management/commands/makemigrations.py b/django/core/management/commands/makemigrations.py
index ec6b71f5a0..2e97d9064b 100644
--- a/django/core/management/commands/makemigrations.py
+++ b/django/core/management/commands/makemigrations.py
@@ -11,6 +11,8 @@ from django.db import DEFAULT_DB_ALIAS, OperationalError, connections, router
 from django.db.migrations import Migration
 from django.db.migrations.autodetector import MigrationAutodetector
 from django.db.migrations.loader import MigrationLoader
+from django.db.migrations.migration import SwappableTuple
+from django.db.migrations.optimizer import MigrationOptimizer
 from django.db.migrations.questioner import (
     InteractiveMigrationQuestioner,
     MigrationQuestioner,
@@ -79,6 +81,15 @@ class Command(BaseCommand):
                 "paths of generated migration files to stdout."
             ),
         )
+        parser.add_argument(
+            "--update",
+            action="store_true",
+            dest="update",
+            help=(
+                "Merge model changes into the latest migration and optimize the "
+                "resulting operations."
+            ),
+        )
 
     @property
     def log_output(self):
@@ -101,6 +112,7 @@ class Command(BaseCommand):
         self.include_header = options["include_header"]
         check_changes = options["check_changes"]
         self.scriptable = options["scriptable"]
+        self.update = options["update"]
         # If logs and prompts are diverted to stderr, remove the ERROR style.
         if self.scriptable:
             self.stderr.style_func = None
@@ -236,11 +248,86 @@ class Command(BaseCommand):
                 else:
                     self.log("No changes detected")
         else:
-            self.write_migration_files(changes)
+            if self.update:
+                self.write_to_last_migration_files(changes)
+            else:
+                self.write_migration_files(changes)
             if check_changes:
                 sys.exit(1)
 
-    def write_migration_files(self, changes):
+    def write_to_last_migration_files(self, changes):
+        loader = MigrationLoader(connections[DEFAULT_DB_ALIAS])
+        new_changes = {}
+        update_previous_migration_paths = {}
+        for app_label, app_migrations in changes.items():
+            # Find last migration.
+            leaf_migration_nodes = loader.graph.leaf_nodes(app=app_label)
+            if len(leaf_migration_nodes) == 0:
+                raise CommandError(
+                    f"App {app_label} has no migration, cannot update last migration."
+                )
+            leaf_migration_node = leaf_migration_nodes[0]
+            # Multiple leaf nodes have already been checked earlier in command.
+            leaf_migration = loader.graph.nodes[leaf_migration_node]
+            # Updated migration cannot be a squash migration, a dependency of
+            # another migration, and cannot be already applied.
+            if leaf_migration.replaces:
+                raise CommandError(
+                    f"Cannot update squash migration '{leaf_migration}'."
+                )
+            if leaf_migration_node in loader.applied_migrations:
+                raise CommandError(
+                    f"Cannot update applied migration '{leaf_migration}'."
+                )
+            depending_migrations = [
+                migration
+                for migration in loader.disk_migrations.values()
+                if leaf_migration_node in migration.dependencies
+            ]
+            if depending_migrations:
+                formatted_migrations = ", ".join(
+                    [f"'{migration}'" for migration in depending_migrations]
+                )
+                raise CommandError(
+                    f"Cannot update migration '{leaf_migration}' that migrations "
+                    f"{formatted_migrations} depend on."
+                )
+            # Build new migration.
+            for migration in app_migrations:
+                leaf_migration.operations.extend(migration.operations)
+
+                for dependency in migration.dependencies:
+                    if isinstance(dependency, SwappableTuple):
+                        if settings.AUTH_USER_MODEL == dependency.setting:
+                            leaf_migration.dependencies.append(
+                                ("__setting__", "AUTH_USER_MODEL")
+                            )
+                        else:
+                            leaf_migration.dependencies.append(dependency)
+                    elif dependency[0] != migration.app_label:
+                        leaf_migration.dependencies.append(dependency)
+            # Optimize migration.
+            optimizer = MigrationOptimizer()
+            leaf_migration.operations = optimizer.optimize(
+                leaf_migration.operations, app_label
+            )
+            # Update name.
+            previous_migration_path = MigrationWriter(leaf_migration).path
+            suggested_name = (
+                leaf_migration.name[:4] + "_" + leaf_migration.suggest_name()
+            )
+            if leaf_migration.name == suggested_name:
+                new_name = leaf_migration.name + "_updated"
+            else:
+                new_name = suggested_name
+            leaf_migration.name = new_name
+            # Register overridden migration.
+            new_changes[app_label] = [leaf_migration]
+            update_previous_migration_paths[app_label] = previous_migration_path
+
+        self.write_migration_files(new_changes, update_previous_migration_paths)
+
+    def write_migration_files(self, changes, update_previous_migration_paths=None):
         """
         Take a changes dict and write them out as migration files.
         """
@@ -274,6 +361,22 @@ class Command(BaseCommand):
                     with open(writer.path, "w", encoding="utf-8") as fh:
                         fh.write(migration_string)
                         self.written_files.append(writer.path)
+                    if update_previous_migration_paths:
+                        prev_path = update_previous_migration_paths[app_label]
+                        rel_prev_path = self.get_relative_path(prev_path)
+                        if writer.needs_manual_porting:
+                            migration_path = self.get_relative_path(writer.path)
+                            self.log(
+                                self.style.WARNING(
+                                    f"Updated migration {migration_path} requires "
+                                    f"manual porting.\n"
+                                    f"Previous migration {rel_prev_path} was kept and "
+                                    f"must be deleted after porting functions manually."
+                                )
+                            )
+                        else:
+                            os.remove(prev_path)
+                            self.log(f"Deleted {rel_prev_path}")
                 elif self.verbosity == 3:
                     # Alternatively, makemigrations --dry-run --verbosity 3
                     # will log the migrations rather than saving the file to
diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index 25a1107c55..5016b25ea2 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -832,6 +832,13 @@ migrations are detected.
 Diverts log output and input prompts to ``stderr``, writing only paths of
 generated migration files to ``stdout``.
 
+.. django-admin-option:: --update
+
+.. versionadded:: 4.2
+
+Merges model changes into the latest migration and optimize the resulting
+operations.
+
 ``migrate``
 -----------
 
diff --git a/docs/releases/4.2.txt b/docs/releases/4.2.txt
index 345f4d4ad8..d43d391408 100644
--- a/docs/releases/4.2.txt
+++ b/docs/releases/4.2.txt
@@ -158,6 +158,9 @@ Management Commands
 * :djadmin:`makemessages` command now supports locales with private sub-tags
   such as ``nl_NL-x-informal``.
 
+* The new :option:`makemigrations --update` option merges model changes into
+  the latest migration and optimizes the resulting operations.
+
 Migrations
 ~~~~~~~~~~
 
diff --git a/tests/migrations/test_commands.py b/tests/migrations/test_commands.py
index a3e1efc924..3c98ddd8db 100644
--- a/tests/migrations/test_commands.py
+++ b/tests/migrations/test_commands.py
@@ -2584,6 +2584,108 @@ class MakeMigrationsTests(MigrationTestBase):
             out_value = out.getvalue()
             self.assertIn("0003_auto", out_value)
 
+    def test_makemigrations_update(self):
+        with self.temporary_migration_module(
+            module="migrations.test_migrations"
+        ) as migration_dir:
+            migration_file = os.path.join(migration_dir, "0002_second.py")
+            with open(migration_file) as fp:
+                initial_content = fp.read()
+
+            with captured_stdout() as out:
+                call_command("makemigrations", "migrations", update=True)
+            self.assertFalse(
+                any(
+                    filename.startswith("0003")
+                    for filename in os.listdir(migration_dir)
+                )
+            )
+            self.assertIs(os.path.exists(migration_file), False)
+            new_migration_file = os.path.join(
+                migration_dir,
+                "0002_delete_tribble_author_rating_modelwithcustombase_and_more.py",
+            )
+            with open(new_migration_file) as fp:
+                self.assertNotEqual(initial_content, fp.read())
+            self.assertIn(f"Deleted {migration_file}", out.getvalue())
+
+    def test_makemigrations_update_existing_name(self):
+        with self.temporary_migration_module(
+            module="migrations.test_auto_now_add"
+        ) as migration_dir:
+            migration_file = os.path.join(migration_dir, "0001_initial.py")
+            with open(migration_file) as fp:
+                initial_content = fp.read()
+
+            with captured_stdout() as out:
+                call_command("makemigrations", "migrations", update=True)
+            self.assertIs(os.path.exists(migration_file), False)
+            new_migration_file = os.path.join(
+                migration_dir,
+                "0001_initial_updated.py",
+            )
+            with open(new_migration_file) as fp:
+                self.assertNotEqual(initial_content, fp.read())
+            self.assertIn(f"Deleted {migration_file}", out.getvalue())
+
+    def test_makemigrations_update_applied_migration(self):
+        recorder = MigrationRecorder(connection)
+        recorder.record_applied("migrations", "0001_initial")
+        recorder.record_applied("migrations", "0002_second")
+        with self.temporary_migration_module(module="migrations.test_migrations"):
+            msg = "Cannot update applied migration 'migrations.0002_second'."
+            with self.assertRaisesMessage(CommandError, msg):
+                call_command("makemigrations", "migrations", update=True)
+
+    def test_makemigrations_update_no_migration(self):
+        with self.temporary_migration_module(module="migrations.test_migrations_empty"):
+            msg = "App migrations has no migration, cannot update last migration."
+            with self.assertRaisesMessage(CommandError, msg):
+                call_command("makemigrations", "migrations", update=True)
+
+    def test_makemigrations_update_squash_migration(self):
+        with self.temporary_migration_module(
+            module="migrations.test_migrations_squashed"
+        ):
+            msg = "Cannot update squash migration 'migrations.0001_squashed_0002'."
+            with self.assertRaisesMessage(CommandError, msg):
+                call_command("makemigrations", "migrations", update=True)
+
+    def test_makemigrations_update_manual_porting(self):
+        with self.temporary_migration_module(
+            module="migrations.test_migrations_plan"
+        ) as migration_dir:
+            with captured_stdout() as out:
+                call_command("makemigrations", "migrations", update=True)
+            # Previous migration exists.
+            previous_migration_file = os.path.join(migration_dir, "0005_fifth.py")
+            self.assertIs(os.path.exists(previous_migration_file), True)
+            # New updated migration exists.
+            files = [f for f in os.listdir(migration_dir) if f.startswith("0005_auto")]
+            updated_migration_file = os.path.join(migration_dir, files[0])
+            self.assertIs(os.path.exists(updated_migration_file), True)
+            self.assertIn(
+                f"Updated migration {updated_migration_file} requires manual porting.\n"
+                f"Previous migration {previous_migration_file} was kept and must be "
+                f"deleted after porting functions manually.",
+                out.getvalue(),
+            )
+
+    @override_settings(
+        INSTALLED_APPS=[
+            "migrations.migrations_test_apps.alter_fk.author_app",
+            "migrations.migrations_test_apps.alter_fk.book_app",
+        ]
+    )
+    def test_makemigrations_update_dependency_migration(self):
+        with self.temporary_migration_module(app_label="book_app"):
+            msg = (
+                "Cannot update migration 'book_app.0001_initial' that migrations "
+                "'author_app.0002_alter_id' depend on."
+            )
+            with self.assertRaisesMessage(CommandError, msg):
+                call_command("makemigrations", "book_app", update=True)
+
 
 class SquashMigrationsTests(MigrationTestBase):
     """