Add create-max-migration-files --recreate (#99)

Fixes #79.

HISTORY.rst

@@ -2,6 +2,11 @@
 History
 =======
 
+* Added ``--recreate`` flag to ``create-max-migration-files``.
+
+  Thanks to Gordon Wrigley for the feature request in `Issue #79
+  <https://github.com/adamchainz/django-linear-migrations/issues/79>`__.
+
 1.6.0 (2021-04-08)
 ------------------
 

README.rst

@@ -96,7 +96,7 @@ If you see any apps listed that *aren’t* part of your project, define the list
     python manage.py create-max-migration-files
 
 In the future, when you add a new app to your project, you’ll need to create its ``max_migration.txt`` file.
-If you defined ``FIRST_PARTY_APPS``, add it there, then rerun the creation command for the new app by specifying its label:
+Add the new app to ``INSTALLED_APPS`` or ``FIRST_PARTY_APPS`` as appropriate, then rerun the creation command for the new app by specifying its label:
 
 .. code-block:: sh
 
@@ -123,6 +123,21 @@ These are:
 * ``dlm.E003``: ``<app_label>``'s max_migration.txt points to non-existent migration '``<bad_migration_name>``'.
 * ``dlm.E004``: ``<app_label>``'s max_migration.txt contains '``<max_migration_name>``', but the latest migration is '``<real_max_migration_name>``'.
 
+``create-max-migration-files`` command
+--------------------------------------
+
+.. code-block:: sh
+
+    python manage.py create-max-migration-files [app_label [app_label ...]]
+
+This management command creates ``max_migration.txt`` files for all first party apps, or the given labels.
+It’s used in initial installation of django-linear-migrations, and for recreating.
+
+Pass the ``--dry-run`` flag to only list the ``max_migration.txt`` files that would be created.
+
+Pass the ``--recreate`` flag to re-create files that already exist.
+This may be useful after altering migrations with merges or manually.
+
 ``rebase-migration`` command
 ----------------------------
 

src/django_linear_migrations/management/commands/create-max-migration-files.py

@@ -8,10 +8,7 @@
 
 
 class Command(BaseCommand):
-    help = (
-        "Generate max_migration.txt files for first-party apps that don't"
-        + " have one."
-    )
+    help = "Generate max_migration.txt files for first-party apps."
 
     # Checks disabled because the django-linear-migrations' checks would
     # prevent us continuing
@@ -33,8 +30,17 @@ def add_arguments(self, parser):
             default=False,
             help="Actually create the files.",
         )
+        parser.add_argument(
+            "--recreate",
+            action="store_true",
+            default=False,
+            help=(
+                "Recreate existing files. By default only non-existing files"
+                + " will be created."
+            ),
+        )
 
-    def handle(self, *app_labels, dry_run, **options):
+    def handle(self, *app_labels, dry_run, recreate, **options):
         # Copied check from makemigrations
         app_labels = set(app_labels)
         has_bad_labels = False
@@ -57,7 +63,7 @@ def handle(self, *app_labels, dry_run, **options):
                 continue
 
             max_migration_txt = migration_details.dir / "max_migration.txt"
-            if not max_migration_txt.exists():
+            if recreate or not max_migration_txt.exists():
                 if not dry_run:
                     max_migration_name = max(migration_details.names)
                     max_migration_txt.write_text(max_migration_name + "\n")

tests/test_create_max_migration_files.py

@@ -114,6 +114,28 @@ def test_success_already_exists(self):
         assert err == ""
         assert returncode == 0
 
+    def test_success_recreate(self):
+        (self.migrations_dir / "__init__.py").touch()
+        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "max_migration.txt").write_text("0001_initial\n")
+
+        out, err, returncode = self.call_command("--recreate")
+
+        assert out == "Created max_migration.txt for testapp.\n"
+        assert err == ""
+        assert returncode == 0
+
+    def test_success_recreate_dry_run(self):
+        (self.migrations_dir / "__init__.py").touch()
+        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "max_migration.txt").write_text("0001_initial\n")
+
+        out, err, returncode = self.call_command("--recreate", "--dry-run")
+
+        assert out == "Would create max_migration.txt for testapp.\n"
+        assert err == ""
+        assert returncode == 0
+
     def test_success_specific_app_label(self):
         (self.migrations_dir / "__init__.py").touch()
         (self.migrations_dir / "0001_initial.py").touch()