Visit function clauses in source order

src/ast/mod.rs

@@ -8218,6 +8218,14 @@ pub struct Function {
     /// The arguments to the function, including any options specified within the
     /// delimiting parentheses.
     pub args: FunctionArguments,
+    /// A clause used with certain aggregate functions to control the ordering
+    /// within grouped sets before the function is applied.
+    ///
+    /// Syntax:
+    /// ```plaintext
+    /// <aggregate_function>(expression) WITHIN GROUP (ORDER BY key [ASC | DESC], ...)
+    /// ```
+    pub within_group: Vec<OrderByExpr>,
     /// e.g. `x > 5` in `COUNT(x) FILTER (WHERE x > 5)`
     pub filter: Option<Box<Expr>>,
     /// Indicates how `NULL`s should be handled in the calculation.
@@ -8231,14 +8239,6 @@ pub struct Function {
     pub null_treatment: Option<NullTreatment>,
     /// The `OVER` clause, indicating a window function call.
     pub over: Option<WindowType>,
-    /// A clause used with certain aggregate functions to control the ordering
-    /// within grouped sets before the function is applied.
-    ///
-    /// Syntax:
-    /// ```plaintext
-    /// <aggregate_function>(expression) WITHIN GROUP (ORDER BY key [ASC | DESC], ...)
-    /// ```
-    pub within_group: Vec<OrderByExpr>,
 }
 
 impl fmt::Display for Function {

src/ast/visitor.rs

@@ -1242,6 +1242,32 @@ mod tests {
         do_visit("SELECT a, b FROM t", &mut visitor);
         assert_eq!(visitor.idents, vec!["a", "b", "t"]);
     }
+
+    #[test]
+    fn visits_function_clauses_in_source_order() {
+        #[derive(Default)]
+        struct ExprVisitor {
+            idents: Vec<String>,
+        }
+
+        impl Visitor for ExprVisitor {
+            type Break = ();
+
+            fn pre_visit_expr(&mut self, expr: &Expr) -> ControlFlow<Self::Break> {
+                if let Expr::Identifier(ident) = expr {
+                    self.idents.push(ident.value.clone());
+                }
+                ControlFlow::Continue(())
+            }
+        }
+
+        let mut visitor = ExprVisitor::default();
+        do_visit(
+            "SELECT LISTAGG(value) WITHIN GROUP (ORDER BY order_key) FILTER (WHERE filter_key)",
+            &mut visitor,
+        );
+        assert_eq!(visitor.idents, ["value", "order_key", "filter_key"]);
+    }
 }
 
 #[cfg(test)]