Build graph plan once for all app labels

src/django_linear_migrations/apps.py

@@ -10,6 +10,7 @@
 from django.apps import AppConfig, apps
 from django.conf import settings
 from django.core.checks import Error, Tags, register
+from django.core.management import CommandError
 from django.core.signals import setting_changed
 from django.db import DEFAULT_DB_ALIAS, connections
 from django.db.migrations.loader import MigrationLoader
@@ -54,6 +55,34 @@ def first_party_app_configs() -> Generator[AppConfig, None, None]:
             yield app_config
 
 
+def get_graph_plan(
+    app_names: Iterable[str] | None = None,
+    database: str = DEFAULT_DB_ALIAS,
+) -> list[tuple[str, str]]:
+    loader = MigrationLoader(connections[database], ignore_no_migrations=True)
+    conflicts = loader.detect_conflicts()
+    if app_names:
+        conflicts = {
+            app_label: conflict
+            for app_label, conflict in conflicts.items()
+            if app_label in app_names
+        }
+    if conflicts:
+        name_str = "; ".join(
+            f"{', '.join(names)} in {app}" for app, names in conflicts.items()
+        )
+        raise CommandError(
+            "Conflicting migrations detected; multiple leaf nodes in the "
+            + f"migration graph: {name_str}.\n"
+            + "To fix them run 'python manage.py makemigrations --merge'"
+        )
+    nodes = loader.graph.leaf_nodes()
+    if app_names:
+        nodes = [key for key in loader.graph.leaf_nodes() if key[0] in app_names]
+    plan = loader.graph._generate_plan(nodes, at_end=True)
+    return cast(list[tuple[str, str]], plan)
+
+
 class MigrationDetails:
     migrations_module_name: str | None
     migrations_module: ModuleType | None
@@ -107,13 +136,6 @@ def names(self) -> set[str]:
             if not is_pkg and name[0] not in "_~"
         }
 
-    @cached_property
-    def plan(self) -> list[tuple[str, str]]:
-        loader = MigrationLoader(connections[DEFAULT_DB_ALIAS])
-        nodes = [key for key in loader.graph.leaf_nodes() if key[0] in self.app_label]
-        plan = loader.graph._generate_plan(nodes, at_end=True)
-        return cast(list[tuple[str, str]], plan)
-
 
 def check_max_migration_files(
     *, app_configs: Iterable[AppConfig] | None = None, **kwargs: object
@@ -124,6 +146,7 @@ def check_max_migration_files(
     else:
         app_config_set = set()
 
+    graph_plan = get_graph_plan(app_names=[a.label for a in first_party_app_configs()])
     for app_config in first_party_app_configs():
         # When only checking certain apps, skip the others
         if app_configs is not None and app_config not in app_config_set:
@@ -181,7 +204,7 @@ def check_max_migration_files(
             )
             continue
 
-        _, real_max_migration_name = migration_details.plan[-1]
+        real_max_migration_name = [k[1] for k in graph_plan if k[0] == app_label][-1]
         if max_migration_name != real_max_migration_name:
             errors.append(
                 Error(

src/django_linear_migrations/management/commands/create_max_migration_files.py

@@ -7,7 +7,11 @@
 from django.apps import apps
 from django.core.management.commands.makemigrations import Command as BaseCommand
 
-from django_linear_migrations.apps import MigrationDetails, first_party_app_configs
+from django_linear_migrations.apps import (
+    MigrationDetails,
+    first_party_app_configs,
+    get_graph_plan,
+)
 
 
 class Command(BaseCommand):
@@ -56,6 +60,7 @@ def handle(
             sys.exit(2)
 
         any_created = False
+        graph_plan = get_graph_plan(app_names=labels)
         for app_config in first_party_app_configs():
             if labels and app_config.label not in labels:
                 continue
@@ -67,7 +72,9 @@ def handle(
             max_migration_txt = migration_details.dir / "max_migration.txt"
             if recreate or not max_migration_txt.exists():
                 if not dry_run:
-                    _, max_migration_name = migration_details.plan[-1]
+                    max_migration_name = [
+                        k[1] for k in graph_plan if k[0] == app_config.label
+                    ][-1]
                     max_migration_txt.write_text(max_migration_name + "\n")
                     self.stdout.write(
                         f"Created max_migration.txt for {app_config.label}."

tests/test_checks.py

@@ -5,9 +5,11 @@
 from textwrap import dedent
 
 import pytest
+from django.core.management import CommandError
 from django.test import TestCase, override_settings
 
 from django_linear_migrations.apps import check_max_migration_files
+from tests.utils import empty_migration
 
 
 class CheckMaxMigrationFilesTests(TestCase):
@@ -54,7 +56,7 @@ def test_skipped_unspecified_app(self):
 
     def test_dlm_E001(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
 
         result = check_max_migration_files()
 
@@ -64,7 +66,7 @@ def test_dlm_E001(self):
 
     def test_dlm_E002(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
         (self.migrations_dir / "max_migration.txt").write_text("line1\nline2\n")
 
         result = check_max_migration_files()
@@ -75,7 +77,7 @@ def test_dlm_E002(self):
 
     def test_dlm_E003(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
         (self.migrations_dir / "max_migration.txt").write_text("0001_start\n")
 
         result = check_max_migration_files()
@@ -89,21 +91,13 @@ def test_dlm_E003(self):
 
     def test_dlm_E004(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").write_text(
-            dedent(
-                """
-                from django.db import migrations
-                class Migration(migrations.Migration):
-                    pass
-                """
-            )
-        )
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
         (self.migrations_dir / "0002_updates.py").write_text(
             dedent(
                 """
                 from django.db import migrations
                 class Migration(migrations.Migration):
-                    pass
+                    dependencies = [('testapp', '0001_initial')]
                 """
             )
         )
@@ -118,17 +112,51 @@ class Migration(migrations.Migration):
             + " latest migration is '0002_updates'."
         )
 
-    def test_okay(self):
-        migrations_txt = dedent(
-            """
-            from django.db import migrations
-            class Migration(migrations.Migration):
-                pass
-            """
+    def test_dlm_E005(self):
+        (self.migrations_dir / "__init__.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
+        (self.migrations_dir / "custom_name.py").write_text(
+            dedent(
+                """
+                from django.db import migrations
+                class Migration(migrations.Migration):
+                    dependencies = [('testapp', '0001_initial')]
+                """
+            )
+        )
+        (self.migrations_dir / "0002_updates.py").write_text(
+            dedent(
+                """
+                from django.db import migrations
+                class Migration(migrations.Migration):
+                    dependencies = [('testapp', '0001_initial')]
+                """
+            )
         )
+        (self.migrations_dir / "max_migration.txt").write_text("0002_updates\n")
+
+        with pytest.raises(CommandError):
+            result = check_max_migration_files()
+            assert len(result) == 1
+            assert result[0].id == "dlm.E005"
+            assert (
+                result[0].msg
+                == "Conflicting migrations detected; multiple leaf nodes"
+                + " in the migration graph: 0002_updates, custom_name in testapp."
+            )
+
+    def test_okay(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").write_text(migrations_txt)
-        (self.migrations_dir / "0002_updates.py").write_text(migrations_txt)
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
+        (self.migrations_dir / "0002_updates.py").write_text(
+            dedent(
+                """
+                from django.db import migrations
+                class Migration(migrations.Migration):
+                    dependencies = [('testapp', '0001_initial')]
+                """
+            )
+        )
         (self.migrations_dir / "max_migration.txt").write_text("0002_updates\n")
 
         result = check_max_migration_files()

tests/test_create_max_migration_files.py

@@ -9,6 +9,8 @@
 from django.core.management import call_command
 from django.test import TestCase, override_settings
 
+from tests.utils import empty_migration
+
 
 class CreateMaxMigrationFilesTests(TestCase):
     @pytest.fixture(autouse=True)
@@ -77,7 +79,7 @@ def test_success_only_init(self):
     @override_settings(FIRST_PARTY_APPS=[])
     def test_success_setting_not_first_party(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
 
         out, err, returncode = self.call_command()
 
@@ -87,7 +89,7 @@ def test_success_setting_not_first_party(self):
 
     def test_success_dry_run(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
 
         out, err, returncode = self.call_command("--dry-run")
 
@@ -99,15 +101,7 @@ def test_success_dry_run(self):
 
     def test_success(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").write_text(
-            dedent(
-                """
-                from django.db import migrations
-                class Migration(migrations.Migration):
-                    pass
-                """
-            )
-        )
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
 
         out, err, returncode = self.call_command()
 
@@ -119,7 +113,7 @@ class Migration(migrations.Migration):
 
     def test_success_already_exists(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
         (self.migrations_dir / "max_migration.txt").write_text("0001_initial\n")
 
         out, err, returncode = self.call_command()
@@ -130,15 +124,7 @@ def test_success_already_exists(self):
 
     def test_success_recreate(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").write_text(
-            dedent(
-                """
-                from django.db import migrations
-                class Migration(migrations.Migration):
-                    pass
-                """
-            )
-        )
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
         (self.migrations_dir / "max_migration.txt").write_text("0001_initial\n")
 
         out, err, returncode = self.call_command("--recreate")
@@ -149,7 +135,7 @@ class Migration(migrations.Migration):
 
     def test_success_recreate_dry_run(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").touch()
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
         (self.migrations_dir / "max_migration.txt").write_text("0001_initial\n")
 
         out, err, returncode = self.call_command("--recreate", "--dry-run")
@@ -160,15 +146,7 @@ def test_success_recreate_dry_run(self):
 
     def test_success_specific_app_label(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").write_text(
-            dedent(
-                """
-                from django.db import migrations
-                class Migration(migrations.Migration):
-                    pass
-                """
-            )
-        )
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
 
         out, err, returncode = self.call_command("testapp")
 
@@ -196,15 +174,7 @@ def test_success_ignored_app_label(self):
 
     def test_success_custom_migration_name(self):
         (self.migrations_dir / "__init__.py").touch()
-        (self.migrations_dir / "0001_initial.py").write_text(
-            dedent(
-                """
-                from django.db import migrations
-                class Migration(migrations.Migration):
-                    pass
-                """
-            )
-        )
+        (self.migrations_dir / "0001_initial.py").write_text(empty_migration())
         (self.migrations_dir / "custom_name.py").write_text(
             dedent(
                 """