[ENG-3476]Setting State Vars that are not defined should raise an error

reflex/state.py

@@ -74,6 +74,7 @@
  EventHandlerShadowsBuiltInStateMethod,
  ImmutableStateError,
  LockExpiredError,
+ SetUndefinedStateVarError,
 )
 from reflex.utils.exec import is_testing_env
 from reflex.utils.serializers import serializer
@@ -1260,6 +1261,9 @@ def __setattr__(self, name: str, value: Any):
  Args:
  name: The name of the attribute.
  value: The value of the attribute.
+
+ Raises:
+ SetUndefinedStateVarError: If a value of a var is set without first defining it.
  """
  if isinstance(value, MutableProxy):
  # unwrap proxy objects when assigning back to the state
@@ -1277,6 +1281,17 @@ def __setattr__(self, name: str, value: Any):
  self._mark_dirty()
  return
 
+ if (
+ not name.startswith("__")
+ and not name.startswith(f"_{type(self).__name__}__")
+ and name not in self.vars
+ and name not in self.get_skip_vars()
+ ):
+ raise SetUndefinedStateVarError(
+ f"The state variable '{name}' has not been defined in '{type(self).__name__}'. "
+ f"All state variables must be declared before they can be set."
+ )
+
  # Set the attribute.
  super().__setattr__(name, value)
 

reflex/utils/exceptions.py

@@ -115,3 +115,7 @@ class PrimitiveUnserializableToJSON(ReflexError, ValueError):
 
 class InvalidLifespanTaskType(ReflexError, TypeError):
  """Raised when an invalid task type is registered as a lifespan task."""
+
+
+class SetUndefinedStateVarError(ReflexError, AttributeError):
+ """Raised when setting the value of a var without first declaring it."""

tests/units/test_state.py

@@ -41,6 +41,7 @@
 )
 from reflex.testing import chdir
 from reflex.utils import format, prerequisites, types
+from reflex.utils.exceptions import SetUndefinedStateVarError
 from reflex.utils.format import json_dumps
 from reflex.vars.base import ComputedVar, Var
 from tests.units.states.mutation import MutableSQLAModel, MutableTestState
@@ -3262,3 +3263,45 @@ def test_child_mixin_state() -> None:
 
  assert "computed" in ChildUsesMixinState.inherited_vars
  assert "computed" not in ChildUsesMixinState.computed_vars
+
+
+def test_assignment_to_undeclared_vars():
+ """Test that an attribute error is thrown when undeclared vars are set."""
+
+ class State(BaseState):
+ val: str
+ _val: str
+ __val: str # type: ignore
+
+ def handle_supported_regular_vars(self):
+ self.val = "no underscore"
+ self._val = "single leading underscore"
+ self.__val = "double leading undercore"
+
+ def handle_regular_var(self):
+ self.num = 5
+
+ def handle_backend_var(self):
+ self._num = 5
+
+ def handle_non_var(self):
+ self.__num = 5
+
+ class Substate(State):
+ def handle_var(self):
+ self.value = 20
+
+ state = State() # type: ignore
+ sub_state = Substate() # type: ignore
+
+ with pytest.raises(SetUndefinedStateVarError):
+ state.handle_regular_var()
+
+ with pytest.raises(SetUndefinedStateVarError):
+ sub_state.handle_var()
+
+ with pytest.raises(SetUndefinedStateVarError):
+ state.handle_backend_var()
+
+ state.handle_supported_regular_vars()
+ state.handle_non_var()