docs: Window::try_new_with_schema with a descriptive error message

datafusion/expr/src/logical_plan/plan.rs

@@ -2543,16 +2543,22 @@ impl Window {
         )
     }
 
+    /// Create a new window function using the provided schema to avoid the overhead of
+    /// building the schema again when the schema is already known.
+    ///
+    /// This method should only be called when you are absolutely sure that the schema being
+    /// provided is correct for the window function. If in doubt, call [try_new](Self::try_new) instead.
     pub fn try_new_with_schema(
         window_expr: Vec<Expr>,
         input: Arc<LogicalPlan>,
         schema: DFSchemaRef,
     ) -> Result<Self> {
-        if window_expr.len() != schema.fields().len() - input.schema().fields().len() {
+        let input_fields_count = input.schema().fields().len();
+        if schema.fields().len() != input_fields_count + window_expr.len() {
             return plan_err!(
-                "Window has mismatch between number of expressions ({}) and number of fields in schema ({})",
-                window_expr.len(),
-                schema.fields().len() - input.schema().fields().len()
+                "Window schema has wrong number of fields. Expected {} got {}",
+                input_fields_count + window_expr.len(),
+                schema.fields().len()
             );
         }