change default session timeout from 0 to 60 minutes

This enables sessions by default.

changelog/6934.removal.md

@@ -0,0 +1,12 @@
+[Conversation sessions](domain.mdx#session-configuration) are now enabled by default
+if your [Domain](domain.mdx) does not contain a session configuration.
+Previously a missing session configuration was treated as if conversation sessions
+were disabled. You can explicitly disable conversation sessions using the following 
+snippet:
+
+```yaml-rasa title="domain.yml"
+session_config:
+  # A session expiration time of `0`
+  # disables conversation sessions
+  session_expiration_time: 0
+```

docs/docs/migration-guide.mdx

@@ -29,6 +29,18 @@ how you can migrate from one version to another.
   component in your `policies` configuration (`config.yml`) you can replace it
   with `TEDPolicy`. It accepts the same configuration parameters.
 
+* [Conversation sessions](domain.mdx#session-configuration) are now enabled by default
+  if your [Domain](domain.mdx) does not contain a session configuration. Previously a
+  missing session configuration was treated as if conversation sessions were disabled.
+  You can explicitly disable conversation sessions using the following snippet:
+
+  ```yaml-rasa title="domain.yml"
+  session_config:
+    # A session expiration time of `0`
+    # disables conversation sessions
+    session_expiration_time: 0
+  ```
+
 ### Training data files
 
 You can convert existing NLU, Stories, and NLG (i.e. `responses.md`) training data

rasa/shared/constants.py

@@ -32,7 +32,7 @@
 
 DOMAIN_SCHEMA_FILE = "utils/schemas/domain.yml"
 
-DEFAULT_SESSION_EXPIRATION_TIME_IN_MINUTES = 0
+DEFAULT_SESSION_EXPIRATION_TIME_IN_MINUTES = 60
 DEFAULT_CARRY_OVER_SLOTS_TO_NEW_SESSION = True
 
 DEFAULT_NLU_FALLBACK_INTENT_NAME = "nlu_fallback"

rasa/shared/core/domain.py

@@ -86,7 +86,6 @@ class SessionConfig(NamedTuple):
 
     @staticmethod
     def default() -> "SessionConfig":
-        # TODO: 2.0, reconsider how to apply sessions to old projects
         return SessionConfig(
             rasa.shared.constants.DEFAULT_SESSION_EXPIRATION_TIME_IN_MINUTES,
             rasa.shared.constants.DEFAULT_CARRY_OVER_SLOTS_TO_NEW_SESSION,
@@ -185,7 +184,6 @@ def from_dict(cls, data: Dict) -> "Domain":
     def _get_session_config(session_config: Dict) -> SessionConfig:
         session_expiration_time_min = session_config.get(SESSION_EXPIRATION_TIME_KEY)
 
-        # TODO: 2.0 reconsider how to apply sessions to old projects and legacy trackers
         if session_expiration_time_min is None:
             session_expiration_time_min = (
                 rasa.shared.constants.DEFAULT_SESSION_EXPIRATION_TIME_IN_MINUTES