Add OutputAdapter sede for custom filters (#6985)

haystack/components/converters/output_adapter.py

@@ -6,6 +6,7 @@
 from typing_extensions import TypeAlias
 
 from haystack import component, default_to_dict, default_from_dict
+from haystack.utils.callable_serialization import serialize_callable, deserialize_callable
 from haystack.utils.type_serialization import serialize_type, deserialize_type
 
 
@@ -124,13 +125,17 @@ def run(self, **kwargs):
         return adapted_outputs
 
     def to_dict(self) -> Dict[str, Any]:
-        # todo should we serialize the custom filters? And if so, can we do the same as for callback handlers?
-        return default_to_dict(self, template=self.template, output_type=serialize_type(self.output_type))
+        se_filters = {name: serialize_callable(filter_func) for name, filter_func in self.custom_filters.items()}
+        return default_to_dict(
+            self, template=self.template, output_type=serialize_type(self.output_type), custom_filters=se_filters
+        )
 
     @classmethod
     def from_dict(cls, data: Dict[str, Any]) -> "OutputAdapter":
         init_params = data.get("init_parameters", {})
         init_params["output_type"] = deserialize_type(init_params["output_type"])
+        for name, filter_func in init_params.get("custom_filters", {}).items():
+            init_params["custom_filters"][name] = deserialize_callable(filter_func) if filter_func else None
         return default_from_dict(cls, data)
 
     def _extract_variables(self, env: NativeEnvironment) -> Set[str]:

test/components/converters/test_output_adapter.py

@@ -7,6 +7,14 @@
 from haystack.components.converters.output_adapter import OutputAdaptationException
 
 
+def custom_filter_to_sede(value):
+    return value.upper()
+
+
+def another_custom_filter(value):
+    return value.upper()
+
+
 class TestOutputAdapter:
     #  OutputAdapter can be initialized with a valid Jinja2 template string and output type.
     def test_initialized_with_valid_template_and_output_type(self):
@@ -84,6 +92,40 @@ def test_sede(self):
         assert adapter.template == deserialized_adapter.template
         assert adapter.output_type == deserialized_adapter.output_type
 
+    # OutputAdapter can be serialized to a dictionary and deserialized along with custom filters
+    def test_sede_with_custom_filters(self):
+        # NOTE: filters need to be declared in a namespace visible to the deserialization function
+        custom_filters = {"custom_filter": custom_filter_to_sede}
+        adapter = OutputAdapter(
+            template="{{ documents[0].content|custom_filter }}", output_type=str, custom_filters=custom_filters
+        )
+        adapter_dict = adapter.to_dict()
+        deserialized_adapter = OutputAdapter.from_dict(adapter_dict)
+
+        assert adapter.template == deserialized_adapter.template
+        assert adapter.output_type == deserialized_adapter.output_type
+        assert adapter.custom_filters == deserialized_adapter.custom_filters == custom_filters
+
+        # invoke the custom filter to check if it is deserialized correctly
+        assert deserialized_adapter.custom_filters["custom_filter"]("test") == "TEST"
+
+    # OutputAdapter can be serialized to a dictionary and deserialized along with multiple custom filters
+    def test_sede_with_multiple_custom_filters(self):
+        # NOTE: filters need to be declared in a namespace visible to the deserialization function
+        custom_filters = {"custom_filter": custom_filter_to_sede, "another_custom_filter": another_custom_filter}
+        adapter = OutputAdapter(
+            template="{{ documents[0].content|custom_filter }}", output_type=str, custom_filters=custom_filters
+        )
+        adapter_dict = adapter.to_dict()
+        deserialized_adapter = OutputAdapter.from_dict(adapter_dict)
+
+        assert adapter.template == deserialized_adapter.template
+        assert adapter.output_type == deserialized_adapter.output_type
+        assert adapter.custom_filters == deserialized_adapter.custom_filters == custom_filters
+
+        # invoke the custom filter to check if it is deserialized correctly
+        assert deserialized_adapter.custom_filters["custom_filter"]("test") == "TEST"
+
     def test_output_adapter_in_pipeline(self):
         @component
         class DocumentProducer: