fix(formatter): preserve type cast comments on rest parameters

crates/oxc_formatter/src/ast_nodes/generated/ast_nodes.rs

@@ -4274,13 +4274,7 @@ impl<'a> AstNode<'a, FormalParameters<'a>> {
 
     #[inline]
     pub fn items(&self) -> &AstNode<'a, Vec<'a, FormalParameter<'a>>> {
-        let following_span_start = self
-            .inner
-            .rest
-            .as_deref()
-            .map(|n| n.span().start)
-            .or(Some(self.following_span_start))
-            .unwrap_or(0);
+        let following_span_start = self.inner.rest.as_deref().map_or(0, |n| n.span().start);
         self.allocator.alloc(AstNode {
             inner: &self.inner.items,
             allocator: self.allocator,
@@ -4291,7 +4285,7 @@ impl<'a> AstNode<'a, FormalParameters<'a>> {
 
     #[inline]
     pub fn rest(&self) -> Option<&AstNode<'a, FormalParameterRest<'a>>> {
-        let following_span_start = self.following_span_start;
+        let following_span_start = 0;
         self.allocator
             .alloc(self.inner.rest.as_ref().map(|inner| AstNode {
                 inner: inner.as_ref(),

crates/oxc_formatter/src/ast_nodes/iterator.rs

@@ -243,7 +243,6 @@ impl_ast_node_vec!(AssignmentTargetProperty<'a>);
 impl_ast_node_vec!(VariableDeclarator<'a>);
 impl_ast_node_vec!(SwitchCase<'a>);
 impl_ast_node_vec!(BindingProperty<'a>);
-impl_ast_node_vec!(FormalParameter<'a>);
 impl_ast_node_vec!(ClassElement<'a>);
 impl_ast_node_vec!(ImportDeclarationSpecifier<'a>);
 impl_ast_node_vec!(ImportAttribute<'a>);
@@ -265,6 +264,10 @@ impl_ast_node_vec_for_option!(Option<BindingPattern<'a>>);
 // Directive needs `following_span_start` to distinguish trailing comments from leading comments
 // of the first statement. See the struct field comment for `following_span_start` for details.
 impl_ast_node_vec!(Directive<'a>, has_following_span_in_the_last_item);
+// FormalParameter needs `following_span_start` to correctly attribute comments between
+// the last parameter and the rest parameter (e.g., `param, /** @type {string[]} */ ...rest`).
+impl_ast_node_vec!(FormalParameter<'a>, has_following_span_in_the_last_item);
+
 // Custom get_span for Statement to handle decorated exports.
 // <https://github.com/oxc-project/oxc/issues/10409>
 impl_ast_node_vec!(Statement<'a>, false, get_statement_span);

crates/oxc_formatter/tests/fixtures/js/ignore/issue-18589.js

@@ -0,0 +1,2 @@
+// type cast on rest parameter should stay after comma
+(/** @type {string} */ param, /** @type {string[]} */ ...rest) => {};

crates/oxc_formatter/tests/fixtures/js/ignore/issue-18589.js.snap

@@ -0,0 +1,21 @@
+---
+source: crates/oxc_formatter/tests/fixtures/mod.rs
+---
+==================== Input ====================
+// type cast on rest parameter should stay after comma
+(/** @type {string} */ param, /** @type {string[]} */ ...rest) => {};
+
+==================== Output ====================
+------------------
+{ printWidth: 80 }
+------------------
+// type cast on rest parameter should stay after comma
+(/** @type {string} */ param, /** @type {string[]} */ ...rest) => {};
+
+-------------------
+{ printWidth: 100 }
+-------------------
+// type cast on rest parameter should stay after comma
+(/** @type {string} */ param, /** @type {string[]} */ ...rest) => {};
+
+===================== End =====================

tasks/ast_tools/src/generators/formatter/ast_nodes.rs

@@ -21,9 +21,11 @@ pub fn get_node_type(ty: &TokenStream) -> TokenStream {
     quote! { AstNode<'a, #ty> }
 }
 
-/// Based on the printing comments algorithm, the last child of these AST nodes don't need to print comments.
-/// Without following nodes could lead to only print comments that before the end of the node, which is what we want.
-const AST_NODE_WITHOUT_FOLLOWING_NODE_LIST: &[&str] = &[];
+/// AST nodes whose last child should have `following_span_start = 0`.
+///
+/// This ensures trailing comments are correctly attributed to the last child itself,
+/// rather than being treated as leading comments of a following sibling outside the parent.
+const AST_NODE_WITHOUT_FOLLOWING_NODE_LIST: &[&str] = &["FormalParameters"];
 
 const AST_NODE_WITH_FOLLOWING_NODE_LIST: &[&str] = &["Function", "Class"];