type check for event handler if spec arg are typed

reflex/components/radix/themes/components/slider.py

@@ -13,6 +13,10 @@ from ..base import (
 )
 
 
+def _on_change_spec(value: List[Union[float, int]]):
+    return [value]
+
+
 class Slider(RadixThemesComponent):
     """Provides user selection from a range of values."""
 
@@ -64,7 +68,7 @@ class Slider(RadixThemesComponent):
     _rename_props = {"onChange": "onValueChange"}
 
     # Fired when the value of the slider changes.
-    on_change: EventHandler[lambda e0: [e0]]
+    on_change: EventHandler[_on_change_spec]
 
     # Fired when a thumb is released after being dragged.
     on_value_commit: EventHandler[lambda e0: [e0]]

reflex/event.py

@@ -22,7 +22,11 @@ from typing_extensions import get_args, get_origin
 
 from reflex import constants
 from reflex.utils import format
-from reflex.utils.exceptions import EventFnArgMismatch, EventHandlerArgMismatch
+from reflex.utils.exceptions import (
+    EventFnArgMismatch,
+    EventHandlerArgMismatch,
+    EventHandlerArgTypeMismatch,
+)
 from reflex.utils.types import ArgsSpec, GenericType
 from reflex.vars import VarData
 from reflex.vars.base import LiteralVar, Var
@@ -888,6 +892,7 @@ def call_event_handler(
 
     Raises:
         EventHandlerArgMismatch: if number of arguments expected by event_handler doesn't match the spec.
+        EventHandlerArgTypeMismatch: if the annotations of args accepted by event_handler differs from the spec of the event trigger.
 
     Returns:
         The event spec from calling the event handler.
@@ -898,11 +903,12 @@ def call_event_handler(
         # Handle partial application of EventSpec args
         return event_handler.add_args(*parsed_args)
 
-    args = inspect.getfullargspec(event_handler.fn).args
+    fullspec = inspect.getfullargspec(event_handler.fn)
+
+    args = fullspec.args
     n_args = len(args) - 1  # subtract 1 for bound self arg
-    if n_args == len(parsed_args):
-        return event_handler(*parsed_args)  # type: ignore
-    else:
+
+    if n_args != len(parsed_args):
         raise EventHandlerArgMismatch(
             "The number of arguments accepted by "
             f"{event_handler.fn.__qualname__} ({n_args}) "
@@ -911,6 +917,20 @@ def call_event_handler(
             "See https://reflex.dev/docs/events/event-arguments/"
         )
 
+    # check that args of event handler are matching the spec if type hints are provided
+    for arg, arg_type in inspect.getfullargspec(arg_spec).annotations.items():
+        if arg not in fullspec.annotations:
+            continue
+        if arg_type == fullspec.annotations[arg]:
+            print(f"continue for {arg}: {arg_type} == {fullspec.annotations[arg]}")
+            continue
+        else:
+            raise EventHandlerArgTypeMismatch(
+                f"Type mismatch for argument {arg} in {event_handler.fn.__qualname__}. Expected {arg_type} but got {fullspec.annotations[arg]}"
+            )
+
+    return event_handler(*parsed_args)  # type: ignore
+
 
 def unwrap_var_annotation(annotation: GenericType):
     """Unwrap a Var annotation or return it as is if it's not Var[X].

reflex/utils/exceptions.py

@@ -82,7 +82,11 @@ class MatchTypeError(ReflexError, TypeError):
 
 
 class EventHandlerArgMismatch(ReflexError, TypeError):
-    """Raised when the number of args accepted by an EventHandler is differs from that provided by the event trigger."""
+    """Raised when the number of args accepted by an EventHandler differs from that provided by the event trigger."""
+
+
+class EventHandlerArgTypeMismatch(ReflexError, TypeError):
+    """Raised when the annotations of args accepted by an EventHandler differs from the spec of the event trigger."""
 
 
 class EventFnArgMismatch(ReflexError, TypeError):