Auto merge of #15520 - frewsxcv:html-options-collection-selected-index, r=nox

Implement `selectedIndex` IDL attribute on `HTMLOptionsCollection`.

<!-- Reviewable:start -->
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15520)
<!-- Reviewable:end -->

1 files changed, 19 insertions, 0 deletions

diff --git a/components/script/dom/htmloptionscollection.rs b/components/script/dom/htmloptionscollection.rs
index 95478fc30f3..be7031ab8d0 100644
--- a/components/script/dom/htmloptionscollection.rs
+++ b/components/script/dom/htmloptionscollection.rs
@@ -6,6 +6,7 @@ use dom::bindings::codegen::Bindings::ElementBinding::ElementMethods;
 use dom::bindings::codegen::Bindings::HTMLCollectionBinding::HTMLCollectionMethods;
 use dom::bindings::codegen::Bindings::HTMLOptionsCollectionBinding;
 use dom::bindings::codegen::Bindings::HTMLOptionsCollectionBinding::HTMLOptionsCollectionMethods;
+use dom::bindings::codegen::Bindings::HTMLSelectElementBinding::HTMLSelectElementMethods;
 use dom::bindings::codegen::Bindings::NodeBinding::NodeBinding::NodeMethods;
 use dom::bindings::codegen::UnionTypes::{HTMLOptionElementOrHTMLOptGroupElement, HTMLElementOrLong};
 use dom::bindings::error::{Error, ErrorResult};
@@ -183,4 +184,22 @@ impl HTMLOptionsCollectionMethods for HTMLOptionsCollection {
             element.Remove();
         }
     }
+
+    // https://html.spec.whatwg.org/multipage/#dom-htmloptionscollection-selectedindex
+    fn SelectedIndex(&self) -> i32 {
+        self.upcast()
+            .root_node()
+            .downcast::<HTMLSelectElement>()
+            .expect("HTMLOptionsCollection not rooted on a HTMLSelectElement")
+            .SelectedIndex()
+    }
+
+    // https://html.spec.whatwg.org/multipage/#dom-htmloptionscollection-selectedindex
+    fn SetSelectedIndex(&self, index: i32) {
+        self.upcast()
+            .root_node()
+            .downcast::<HTMLSelectElement>()
+            .expect("HTMLOptionsCollection not rooted on a HTMLSelectElement")
+            .SetSelectedIndex(index)
+    }
 }