Fix the priority order of slot mappings in which slots are filled

changelog/11390.bugfix.md

@@ -0,0 +1,2 @@
+Fixes regression in which slot mappings were prioritized according to reverse order as they were listed in the domain, instead of in order from first to last, as was implicitly expected in `2.x`.
+Clarifies this implicit priority order in the docs.

docs/docs/domain.mdx

@@ -531,6 +531,9 @@ based on the latest user message.
 In addition to the predefined mappings, you can define [custom slot mappings](./domain.mdx#custom-slot-mappings).
 All custom slot mappings should contain a mapping of type `custom`.
 
+Slot mappings are specified as a YAML list of dictionaries under the key `mappings` in the domain file.
+Slot mappings are prioritized in the order they are listed in the domain. The first slot mapping found to apply will be used to fill the slot.
+
 The default behavior is for slot mappings to apply after every user message, regardless of the dialogue context.
 To make a slot mapping apply only within the context of a form see [Mapping Conditions](./domain.mdx#mapping-conditions).
 There is one additional default limitation on applying `from_entity` slot mappings in the context of a form;

rasa/core/actions/action.py

@@ -1236,6 +1236,7 @@ async def run(
 
                     if value is not None or tracker.get_slot(slot.name) is not None:
                         slot_events.append(SlotSet(slot.name, value))
+                        break
 
                 should_fill_custom_slot = mapping_type == SlotMappingType.CUSTOM
 

tests/core/test_actions.py

@@ -2732,3 +2732,56 @@ async def test_action_extract_slots_emits_necessary_slot_set_events(
         assert events[0].value == value_to_set
     else:
         assert len(events) == 0
+
+
+async def test_action_extract_slots_priority_of_slot_mappings():
+    slot_name = "location_slot"
+    entity_name = "location"
+    entity_value = "Berlin"
+
+    domain_yaml = textwrap.dedent(
+        f"""
+        version: "{LATEST_TRAINING_DATA_FORMAT_VERSION}"
+
+        intents:
+        - inform
+
+        entities:
+        - {entity_name}
+
+        slots:
+          {slot_name}:
+            type: text
+            influence_conversation: false
+            mappings:
+            - type: from_entity
+              entity: {entity_name}
+            - type: from_intent
+              value: 42
+              intent: inform
+
+        responses:
+            utter_ask_location:
+                - text: "where are you located?"
+        """
+    )
+    domain = Domain.from_yaml(domain_yaml)
+    initial_events = [
+        UserUttered(
+            "I am located in Berlin",
+            intent={"name": "inform"},
+            entities=[{"entity": entity_name, "value": entity_value}],
+        ),
+    ]
+    tracker = DialogueStateTracker.from_events(sender_id="test_id", evts=initial_events)
+
+    action_extract_slots = ActionExtractSlots(None)
+
+    events = await action_extract_slots.run(
+        CollectingOutputChannel(),
+        TemplatedNaturalLanguageGenerator(domain.responses),
+        tracker,
+        domain,
+    )
+    tracker.update_with_events(events, domain=domain)
+    assert tracker.get_slot("location_slot") == entity_value