#v1 Refactor logic for handler resolution and loading checkpointables + additional fallback capabilities for non-standard checkpoint formats.

PiperOrigin-RevId: 869904948

Author: angel-core

checkpoint/CHANGELOG.md

@@ -26,6 +26,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 `load_checkpointables()` each with their own dedicated loading logic
 - Refactor v0 Pytree validation and metadata resolution and add `OrbaxV0Layout`
 tests
+- Refactor `CompositeHandler` logic into the orbax layout objects and handler
+resolution utility, deprecating and deleting the `CompositeHandler` class.
 
 ## [0.11.32] - 2026-01-20
 

checkpoint/orbax/checkpoint/experimental/v1/_src/handlers/composite_handler.py

@@ -392,6 +392,16 @@ def _get_possible_handlers(
   return possible_handlers
 
 
+def get_registered_handler_by_name(
+    registry: CheckpointableHandlerRegistry,
+    name: str,
+) -> CheckpointableHandler | None:
+  """Returns the handler for the given name if registered."""
+  if registry.has(name):
+    return _construct_handler_instance(name, registry.get(name))
+  return None
+
+
 def resolve_handler_for_save(
     registry: CheckpointableHandlerRegistry,
     checkpointable: Any,
@@ -444,7 +454,7 @@ def resolve_handler_for_load(
     abstract_checkpointable: Any | None,
     *,
     name: str,
-    handler_typestr: str,
+    handler_typestr: str | None = None,
 ) -> CheckpointableHandler:
   """Resolves a :py:class:`~.v1.handlers.CheckpointableHandler` for loading.
 
@@ -492,15 +502,16 @@ def is_handleable_fn(
       handler_types.typestr(type(handler)) for handler in possible_handlers
   ]
 
-  try:
-    idx = possible_handler_typestrs.index(handler_typestr)
-    return possible_handlers[idx]
-  except ValueError:
-    logging.warning(
-        'No handler found for typestr %s. The checkpointable may be restored'
-        ' with different handler logic than was used for saving.',
-        handler_typestr,
-    )
+  if handler_typestr:
+    try:
+      idx = possible_handler_typestrs.index(handler_typestr)
+      return possible_handlers[idx]
+    except ValueError:
+      logging.warning(
+          'No handler found for typestr %s. The checkpointable may be restored'
+          ' with different handler logic than was used for saving.',
+          handler_typestr,
+      )
 
   # Prefer the first handler in the absence of any other information.
   return possible_handlers[-1]