make sure Domain.fromDict(domain) doesn't change its input domain

changelog/5794.improvement.rst

@@ -0,0 +1,3 @@
+Creating a ``Domain`` using ``Domain.fromDict`` can no longer alter the input dictionary.
+Previously, there could be problems when the input dictionary was re-used for other
+things after creating the ``Domain`` from it.

rasa/core/domain.py

@@ -134,6 +134,7 @@ def from_yaml(cls, yaml: Text) -> "Domain":
 
     @classmethod
     def from_dict(cls, data: Dict) -> "Domain":
+        data = copy.deepcopy(data)
         utter_templates = cls.collect_templates(data.get("responses", {}))
         if "templates" in data:
             raise_warning(
@@ -259,6 +260,8 @@ def collect_slots(slot_dict: Dict[Text, Any]) -> List[Slot]:
         # it is super important to sort the slots here!!!
         # otherwise state ordering is not consistent
         slots = []
+        # make a copy to not alter the input dictionary
+        slot_dict = copy.deepcopy(slot_dict)
         for slot_name in sorted(slot_dict):
             slot_class = Slot.resolve_by_type(slot_dict[slot_name].get("type"))
             if "type" in slot_dict[slot_name]:
@@ -332,6 +335,8 @@ def collect_intent_properties(
         Returns:
             The intent properties to be stored in the domain.
         """
+        # make a copy to not alter the input argument
+        intents = copy.deepcopy(intents)
         intent_properties = {}
         duplicates = set()
         for intent in intents:

tests/core/test_domain.py

@@ -1,3 +1,4 @@
+import copy
 import json
 from pathlib import Path
 
@@ -802,3 +803,12 @@ def test_domain_utterance_actions_deprecated_templates():
     old_domain = Domain.from_yaml(old_yaml)
     new_domain = Domain.from_yaml(new_yaml)
     assert hash(old_domain) == hash(new_domain)
+
+
+def test_domain_from_dict_does_not_change_input():
+    path = DEFAULT_DOMAIN_PATH_WITH_SLOTS
+    input_before = io_utils.read_yaml(io_utils.read_file(path))
+    input_after = copy.deepcopy(input_before)
+
+    Domain.from_dict(input_after)
+    assert input_after == input_before