fixes #4576

reflex/components/core/foreach.py

@@ -11,6 +11,7 @@ from reflex.components.component import Component
 from reflex.components.tags import IterTag
 from reflex.constants import MemoizationMode
 from reflex.state import ComponentState
+from reflex.utils.exceptions import UntypedVarError
 from reflex.vars.base import LiteralVar, Var
 
 
@@ -72,8 +73,14 @@ class Foreach(Component):
             iterable=iterable,
             render_fn=render_fn,
         )
-        # Keep a ref to a rendered component to determine correct imports/hooks/styles.
-        component.children = [component._render().render_component()]
+        try:
+            # Keep a ref to a rendered component to determine correct imports/hooks/styles.
+            component.children = [component._render().render_component()]
+        except UntypedVarError as e:
+            raise UntypedVarError(
+                f"Could not foreach over var `{iterable!s}` without a type annotation. "
+                "See https://reflex.dev/docs/library/dynamic-rendering/foreach/"
+            ) from e
         return component
 
     def _render(self) -> IterTag:

reflex/utils/exceptions.py

@@ -75,6 +75,10 @@ class VarAttributeError(ReflexError, AttributeError):
     """Custom AttributeError for var related errors."""
 
 
+class UntypedVarError(ReflexError, TypeError):
+    """Custom TypeError for untyped var errors."""
+
+
 class UntypedComputedVarError(ReflexError, TypeError):
     """Custom TypeError for untyped computed var errors."""
 

reflex/vars/base.py

@@ -1216,7 +1216,7 @@ class Var(Generic[VAR_TYPE]):
                 raise TypeError("Cannot reverse non-list var.")
 
             if self._var_type is Any:
-                raise TypeError(
+                raise exceptions.UntypedVarError(
                     f"You must provide an annotation for the state var `{self!s}`. Annotation cannot be `{self._var_type}`."
                 )