Don't try to collect fields that the user has updated and then deleted

If the user updates a field, then deletes it, and the sync runs, we'll need to ignore those fields as the profile doesn't have them anymore.

We would send down the delete, but that isn't implemented yet.

synapse/handlers/sliding_sync/extensions.py

@@ -1267,7 +1267,9 @@ class SlidingSyncExtensionHandler:
                 user_fields = (
                     user_fields
                     if profile_user_id in joined_room_user_ids
-                    else set(updated_user_fields.get(profile_user_id, []))
+                    else set(updated_user_fields.get(profile_user_id, [])).intersection(
+                        profile_data.keys()
+                    )
                 )
                 for field_name in user_fields:
                     # Ensure we don't send the field unnecessarely to the client, if

tests/rest/client/sliding_sync/test_extension_profiles.py

@@ -236,6 +236,71 @@ class SlidingSyncProfilesTestCase(SlidingSyncBase):
                 },
             )
 
+    @override_config({"include_profile_updates_in_sync": True})
+    def test_updated_field_then_deleted_does_not_error(self) -> None:
+        """
+        Test that profile extension response does not crash if the user first
+        updates a field, then deletes it, and then the sync happens seeing both
+        the update and delete in the stream.
+        """
+        self.get_success(
+            self.profile_handler.set_field(
+                target_user=UserID.from_string(self.other_user),
+                requester=create_requester(self.other_user),
+                field_name="field",
+                new_value="value",
+            )
+        )
+        # Make an initial Sliding Sync request with the profiles extension enabled
+        sync_body = {
+            "lists": {},
+            "extensions": {
+                "org.matrix.msc4262.profiles": {
+                    "enabled": True,
+                    "fields": ["field"],
+                },
+            },
+        }
+        response_body, from_token = self.do_sync(sync_body, tok=self.tok)
+        # Starting situation
+        self.assertEqual(
+            response_body["extensions"]["org.matrix.msc4262.profiles"]["users"][
+                "@other_user:test"
+            ],
+            {
+                "updated": {
+                    "field": "value",
+                }
+            },
+        )
+
+        # Update field
+        self.get_success(
+            self.profile_handler.set_field(
+                target_user=UserID.from_string(self.other_user),
+                requester=create_requester(self.other_user),
+                field_name="field",
+                new_value="new value",
+            )
+        )
+        # Delete field
+        self.get_success(
+            self.profile_handler.delete_profile_field(
+                target_user=UserID.from_string(self.other_user),
+                requester=create_requester(self.other_user),
+                field_name="field",
+            )
+        )
+
+        # Make an incremental Sliding Sync request
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=self.tok)
+
+        # FIXME: once field deletions come down in sync this should
+        # be checking for that
+        self.assertIsNone(
+            response_body["extensions"].get("org.matrix.msc4262.profiles")
+        )
+
     @parameterized.expand(
         [
             True,