Fix: add handler name to exceptions in handler validation.

Related: #

litestar/handlers/base.py

@@ -254,6 +254,16 @@ def handler_name(self) -> str:
         """
         return get_name(unwrap_partial(self.fn))
 
+    @property
+    def handler_fullname(self) -> str:
+        """Get the qualified name of the handler function.
+
+        Returns:
+            Qualified name of the handler function
+        """
+        handler_fn = unwrap_partial(self.fn)
+        return handler_fn.__module__ + "." + handler_fn.__qualname__
+
     @property
     def dependency_name_set(self) -> set[str]:
         """Set of all dependency names provided in the handler's ownership layers."""

litestar/handlers/http_handlers/base.py

@@ -574,7 +574,7 @@ def _validate_handler_function(self) -> None:
 
         if return_type.annotation is Empty:
             raise ImproperlyConfiguredException(
-                "A return value of a route handler function should be type annotated. "
+                f"A return value of a route handler function {self.handler_fullname} should be type annotated. "
                 "If your function doesn't return a value, annotate it as returning 'None'."
             )
 

litestar/handlers/http_handlers/decorators.py

@@ -588,7 +588,9 @@ def _validate_handler_function(self) -> None:
             or is_class_and_subclass(return_annotation, File)
             or is_class_and_subclass(return_annotation, ASGIFileResponse)
         ):
-            raise ImproperlyConfiguredException("A response to a head request should not have a body")
+            raise ImproperlyConfiguredException(
+                f"A route handler function '{self.handler_fullname}' that handles HEAD request should not have a body"
+            )
 
 
 class patch(HTTPRouteHandler, _SubclassWarningMixin):

litestar/handlers/websocket_handlers/route_handler.py

@@ -85,17 +85,25 @@ def _validate_handler_function(self) -> None:
         super()._validate_handler_function()
 
         if not self.parsed_fn_signature.return_type.is_subclass_of(NoneType):
-            raise ImproperlyConfiguredException("Websocket handler functions should return 'None'")
+            raise ImproperlyConfiguredException(
+                f"Websocket handler function '{self.handler_fullname}' should return 'None'"
+            )
 
         if "socket" not in self.parsed_fn_signature.parameters:
-            raise ImproperlyConfiguredException("Websocket handlers must set a 'socket' kwarg")
+            raise ImproperlyConfiguredException(
+                f"Websocket handler '{self.handler_fullname}' must set a 'socket' kwarg"
+            )
 
         for param in ("request", "body", "data"):
             if param in self.parsed_fn_signature.parameters:
-                raise ImproperlyConfiguredException(f"The {param} kwarg is not supported with websocket handlers")
+                raise ImproperlyConfiguredException(
+                    f"{self.handler_fullname}: the {param} kwarg is not supported with websocket handlers"
+                )
 
         if not is_async_callable(self.fn):
-            raise ImproperlyConfiguredException("Functions decorated with 'websocket' must be async functions")
+            raise ImproperlyConfiguredException(
+                f"Function '{self.handler_fullname}' decorated with 'websocket' must be async functions"
+            )
 
 
 websocket = WebsocketRouteHandler