ATO-218 Always set slot values

This fixes a bug where slot values vanish when using the augmented
memoization policy. If in the past, the slot is set to a specific value,
and then later the slot being set to the same value, no new SlotSet
event is emitted. However, this leads to the augmented memoiziation
policy wrongly assuming this slot to be unset, as the older, original
SlotSet event was pruned already.

rasa/core/actions/action.py

@@ -1234,7 +1234,7 @@ async def run(
                     if not isinstance(slot, ListSlot):
                         value = value[-1]
 
-                    if tracker.get_slot(slot.name) != value:
+                    if value is not None or slot.value is not None:
                         slot_events.append(SlotSet(slot.name, value))
 
                 should_fill_custom_slot = mapping_type == SlotMappingType.CUSTOM

tests/core/test_actions.py

@@ -2,6 +2,7 @@
 import textwrap
 from datetime import datetime
 from typing import List, Text, Any, Dict, Optional
+from unittest.mock import Mock
 
 import pytest
 from _pytest.logging import LogCaptureFixture
@@ -159,7 +160,6 @@ async def test_remote_action_runs(
     default_tracker: DialogueStateTracker,
     domain: Domain,
 ):
-
     endpoint = EndpointConfig("https://example.com/webhooks/actions")
     remote_action = action.RemoteAction("my_action", endpoint)
 
@@ -467,7 +467,6 @@ async def test_remote_action_invalid_entities_payload(
     domain: Domain,
     event: Event,
 ):
-
     endpoint = EndpointConfig("https://example.com/webhooks/actions")
     remote_action = action.RemoteAction("my_action", endpoint)
     response = {"events": [event], "responses": []}
@@ -1216,7 +1215,7 @@ async def test_action_extract_slots_predefined_mappings(
         tracker,
         domain,
     )
-    assert not new_events
+    assert new_events == [SlotSet(slot_name, slot_value)]
 
     new_events.extend([BotUttered(), ActionExecuted("action_listen"), new_user])
     tracker.update_with_events(new_events, domain)
@@ -2665,3 +2664,51 @@ async def test_action_extract_slots_non_required_form_slot_with_from_entity_mapp
         domain,
     )
     assert events == [SlotSet("form1_info1", "info1"), SlotSet("form1_slot1", "Filled")]
+
+
+async def test_action_extract_slots_returns_slot_set_even_if_slot_value_is_unchanged():
+    event_with_slot_entity = UserUttered(
+        text="I am a text",
+        intent={"name": "intent_with_entity"},
+        entities=[{"entity": "entity", "value": "value"}],
+    )
+
+    domain = textwrap.dedent(
+        """
+          intents:
+            - intent_with_entity
+          entities:
+            - entity
+          slots:
+            entity:
+              type: text
+              mappings:
+              - type: from_entity
+                entity: entity
+        """
+    )
+
+    domain = Domain.from_yaml(domain)
+
+    tracker = DialogueStateTracker.from_events(
+        "some-sender",
+        evts=[
+            event_with_slot_entity,
+        ],
+    )
+
+    tracker._set_slot("entity", "value")
+
+    action = ActionExtractSlots(None)
+
+    events = await action.run(
+        output_channel=CollectingOutputChannel(),
+        nlg=Mock(),
+        tracker=tracker,
+        domain=domain,
+    )
+
+    assert len(events) == 1
+    assert type(events[0]) == SlotSet
+    assert events[0].key == "entity"
+    assert events[0].value == "value"