add type validation to computed vars

reflex/vars/base.py

@@ -63,7 +63,14 @@ from reflex.utils.imports import (
     ParsedImportDict,
     parse_imports,
 )
-from reflex.utils.types import GenericType, Self, get_origin, has_args, unionize
+from reflex.utils.types import (
+    GenericType,
+    Self,
+    _isinstance,
+    get_origin,
+    has_args,
+    unionize,
+)
 
 if TYPE_CHECKING:
     from reflex.state import BaseState
@@ -1833,6 +1840,14 @@ class ComputedVar(Var[RETURN_TYPE]):
             "return", Any
         )
 
+        if hint is Any:
+            console.deprecate(
+                "untyped-computed-var",
+                "ComputedVar should have a return type annotation.",
+                "0.6.5",
+                "0.7.0",
+            )
+
         kwargs.setdefault("_js_expr", fget.__name__)
         kwargs.setdefault("_var_type", hint)
 
@@ -2026,8 +2041,8 @@ class ComputedVar(Var[RETURN_TYPE]):
             )
 
         if not self._cache:
-            return self.fget(instance)
-
+            value = self.fget(instance)
+        else:
             # handle caching
             if not hasattr(instance, self._cache_attr) or self.needs_update(instance):
                 # Set cache attr on state instance.
@@ -2036,7 +2051,18 @@ class ComputedVar(Var[RETURN_TYPE]):
                 instance._was_touched = True
                 # Set the last updated timestamp on the state instance.
                 setattr(instance, self._last_updated_attr, datetime.datetime.now())
-        return getattr(instance, self._cache_attr)
+            value = getattr(instance, self._cache_attr)
+
+        if not _isinstance(value, self._var_type):
+            console.deprecate(
+                "mismatched-computed-var-return",
+                f"Computed var {type(instance).__name__}.{self._js_expr} returned value of type {type(value)}, "
+                f"expected {self._var_type}. This might cause unexpected behavior.",
+                "0.6.5",
+                "0.7.0",
+            )
+
+        return value
 
     def _deps(
         self,