fix: Initials of scxml is respected; Added validate_disconnected_states parameter since scxml don't expect that the graph should have a single component

Author: fgmacedo

docs/releases/3.0.0.md

@@ -100,6 +100,13 @@ TODO: Example of delayed events
 Also, delayed events can be revoked by it's `send_id`.
 
 
+### Disable single graph component validation.
+
+Since SCXML don't require that all states should be reachable by transitions, we added a class-level
+flag `validate_disconnected_states: bool = True` that can be used to disable this validation.
+
+It's already disabled when parsing SCXML files.
+
 
 ## Bugfixes in 3.0.0
 

statemachine/factory.py

@@ -11,9 +11,10 @@
 from .callbacks import CallbackSpecList
 from .event import Event
 from .exceptions import InvalidDefinition
+from .graph import disconnected_states
 from .graph import iterate_states
 from .graph import iterate_states_and_transitions
-from .graph import visit_connected_states
+from .graph import states_without_path_to_final_states
 from .i18n import _
 from .state import State
 from .states import States
@@ -24,6 +25,9 @@
 class StateMachineMetaclass(type):
     "Metaclass for constructing StateMachine classes"
 
+    validate_disconnected_states: bool = True
+    """If `True`, the state machine will validate that there are no unreachable states."""
+
     def __init__(
         cls,
         name: str,
@@ -179,7 +183,7 @@ def _check_trap_states(cls):
     def _check_reachable_final_states(cls):
         if not any(s.final for s in cls.states):
             return  # No need to check final reachability
-        disconnected_states = cls._states_without_path_to_final_states()
+        disconnected_states = list(states_without_path_to_final_states(cls.states))
         if disconnected_states:
             message = _(
                 "All non-final states should have at least one path to a final state. "
@@ -190,26 +194,18 @@ def _check_reachable_final_states(cls):
             else:
                 warnings.warn(message, UserWarning, stacklevel=1)
 
-    def _states_without_path_to_final_states(cls):
-        return [
-            state
-            for state in cls.states
-            if not state.final and not any(s.final for s in visit_connected_states(state))
-        ]
-
-    def _disconnected_states(cls, starting_state):
-        visitable_states = set(visit_connected_states(starting_state))
-        return set(cls.states) - visitable_states
-
     def _check_disconnected_state(cls):
-        disconnected_states = cls._disconnected_states(cls.initial_state)
-        if disconnected_states:
+        if not cls.validate_disconnected_states:
+            return
+        assert cls.initial_state
+        states = disconnected_states(cls.initial_state, set(cls.states_map.values()))
+        if states:
             raise InvalidDefinition(
                 _(
                     "There are unreachable states. "
                     "The statemachine graph should have a single component. "
                     "Disconnected states: {}"
-                ).format([s.id for s in disconnected_states])
+                ).format([s.id for s in states])
             )
 
     def _setup(cls):

statemachine/graph.py

@@ -1,8 +1,14 @@
 from collections import deque
+from typing import TYPE_CHECKING
+from typing import Iterable
+from typing import MutableSet
 
+if TYPE_CHECKING:
+    from .state import State
 
-def visit_connected_states(state):
-    visit = deque()
+
+def visit_connected_states(state: "State"):
+    visit = deque["State"]()
     already_visited = set()
     visit.append(state)
     while visit:
@@ -14,16 +20,29 @@ def visit_connected_states(state):
         visit.extend(t.target for t in state.transitions if t.target)
 
 
-def iterate_states_and_transitions(states):
+def disconnected_states(starting_state: "State", all_states: MutableSet["State"]):
+    visitable_states = set(visit_connected_states(starting_state))
+    return all_states - visitable_states
+
+
+def iterate_states_and_transitions(states: Iterable["State"]):
     for state in states:
         yield state
         yield from state.transitions
         if state.states:
             yield from iterate_states_and_transitions(state.states)
 
 
-def iterate_states(states):
+def iterate_states(states: Iterable["State"]):
     for state in states:
         yield state
         if state.states:
             yield from iterate_states(state.states)
+
+
+def states_without_path_to_final_states(states: Iterable["State"]):
+    return (
+        state
+        for state in states
+        if not state.final and not any(s.final for s in visit_connected_states(state))
+    )

statemachine/io/scxml/parser.py

@@ -92,10 +92,9 @@ def parse_scxml(scxml_content: str) -> StateMachineDefinition:  # noqa: C901
         for state, parents in visit_states(definition.states.values(), []):
             if state.id in definition.initial_states:
                 not_found.remove(state.id)
-                if parents:
-                    topmost_state = parents[0]
-                    topmost_state.initial = True
-                    definition.initial_states.add(topmost_state.id)
+                for parent in parents:
+                    parent.initial = True
+                    definition.initial_states.add(parent.id)
             if not not_found:
                 break
 

statemachine/io/scxml/processor.py

@@ -88,7 +88,14 @@ def process_definition(self, definition, location: str):
                     initial_state["enter"] = []
                 if isinstance(initial_state["enter"], list):
                     initial_state["enter"].insert(0, datamodel)
-        self._add(location, {"states": states_dict, "prepare_event": self._prepare_event})
+        self._add(
+            location,
+            {
+                "states": states_dict,
+                "prepare_event": self._prepare_event,
+                "validate_disconnected_states": False,
+            },
+        )
 
     def _prepare_event(self, *args, **kwargs):
         machine = kwargs["machine"]

tests/scxml/w3c/mandatory/test355.scxml

@@ -6,7 +6,6 @@ we enter s0 first we succeed, if s1, failure. -->
 
   <state id="s0">
     <transition target="pass" />
-    <transition target="s1" cond="1 &lt; 0" /><!-- fgm: added to have a single component in graph -->
   </state>
 
   <state id="s1">

tests/scxml/w3c/mandatory/test413.scxml

@@ -16,7 +16,6 @@ states we should not enter all have immediate transitions to failure in them -->
       we're in
   either s2p112 or s2p122, but not both of them -->
       <transition target="fail" />
-      <transition target="s1" cond="1 &lt; 0" /><!-- fgm: added to have a single component in graph -->
 
       <state id="s2p11" initial="s2p111">
         <state id="s2p111">