fix(alembic): narrow enum-import guard to ModuleNotFoundError

Catching ImportError also swallowed genuine import-time failures (e.g.
version mismatches), silently disabling enum autogenerate support even
when alembic-postgresql-enum is installed. Catch ModuleNotFoundError so
a missing package is handled quietly while real errors surface.

Addresses review feedback on litestar-org#774.

Author: hasansezertasan

advanced_alchemy/alembic/templates/asyncio/env.py

@@ -14,7 +14,7 @@
     # required autogenerate comparators as a side effect. Install with the
     # ``advanced-alchemy[postgresql]`` extra to enable.
     import alembic_postgresql_enum  # type: ignore[import-not-found,unused-ignore]  # pyright: ignore[reportMissingImports]  # noqa: F401
-except ImportError:
+except ModuleNotFoundError:
     pass
 
 if TYPE_CHECKING:

advanced_alchemy/alembic/templates/sync/env.py

@@ -12,7 +12,7 @@
     # required autogenerate comparators as a side effect. Install with the
     # ``advanced-alchemy[postgresql]`` extra to enable.
     import alembic_postgresql_enum  # type: ignore[import-not-found,unused-ignore]  # pyright: ignore[reportMissingImports]  # noqa: F401
-except ImportError:
+except ModuleNotFoundError:
     pass
 
 if TYPE_CHECKING:

tests/integration/test_alembic_commands.py

@@ -246,7 +246,7 @@ async def test_alembic_init_renders_postgres_enum_import(
     alembic_commands.init(directory=f"{tmp_project_dir}/migrations/")
     env_contents = await async_(Path(f"{tmp_project_dir}/migrations/env.py").read_text)()
     assert "import alembic_postgresql_enum" in env_contents
-    assert "except ImportError:" in env_contents
+    assert "except ModuleNotFoundError:" in env_contents
 
 
 async def test_alembic_init_already(alembic_commands: commands.AlembicCommands, tmp_project_dir: Path) -> None: