fix: allow both _composable_pass and composable_pass imports

hugr-py/src/hugr/passes/_composable_pass.py

@@ -0,0 +1,20 @@
+"""A Protocol for a composable pass.
+
+Deprecated module alias for `hugr.passes.composable_pass`.
+"""
+
+from .composable_pass import (
+    ComposablePass,
+    ComposedPass,
+    PassName,
+    PassResult,
+    implement_pass_run,
+)
+
+__all__ = [
+    "PassName",
+    "PassResult",
+    "ComposedPass",
+    "ComposablePass",
+    "implement_pass_run",
+]

hugr-py/src/hugr/passes/composable_pass.py

@@ -1,7 +1,4 @@
-"""A Protocol for a composable pass.
-
-Currently unstable.
-"""
+"""A Protocol for a composable pass."""
 
 from __future__ import annotations
 

hugr-py/tests/test_passes.py

@@ -6,9 +6,14 @@
 import pytest
 
 from hugr.hugr.base import Hugr
-from hugr.passes.composable_pass import (
+
+# Import some items from the deprecated module and some from the stable
+# version to ensure the deprecated module is still functional.
+from hugr.passes._composable_pass import (
     ComposablePass,
     ComposedPass,
+)
+from hugr.passes.composable_pass import (
     PassResult,
     implement_pass_run,
 )