Auto merge of #11697 - mrmiywj:form-index-getter, r=Ms2ger

indexed getter of form elements

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #11405 (github issue number if applicable).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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5 files changed, 36 insertions, 6 deletions

diff --git a/components/script/dom/htmlformelement.rs b/components/script/dom/htmlformelement.rs
index fcc10e3d134..515d49c0f7c 100644
--- a/components/script/dom/htmlformelement.rs
+++ b/components/script/dom/htmlformelement.rs
@@ -6,6 +6,7 @@ use dom::bindings::codegen::Bindings::BlobBinding::BlobMethods;
 use dom::bindings::codegen::Bindings::DocumentBinding::DocumentMethods;
 use dom::bindings::codegen::Bindings::EventBinding::EventMethods;
 use dom::bindings::codegen::Bindings::HTMLButtonElementBinding::HTMLButtonElementMethods;
+use dom::bindings::codegen::Bindings::HTMLFormControlsCollectionBinding::HTMLFormControlsCollectionMethods;
 use dom::bindings::codegen::Bindings::HTMLFormElementBinding;
 use dom::bindings::codegen::Bindings::HTMLFormElementBinding::HTMLFormElementMethods;
 use dom::bindings::codegen::Bindings::HTMLInputElementBinding::HTMLInputElementMethods;
@@ -229,6 +230,12 @@ impl HTMLFormElementMethods for HTMLFormElement {
     fn Length(&self) -> u32 {
         self.Elements().Length() as u32
     }
+
+    // https://html.spec.whatwg.org/multipage/#dom-form-item
+    fn IndexedGetter(&self, index: u32, found: &mut bool) -> Option<Root<Element>> {
+        let elements = self.Elements();
+        elements.IndexedGetter(index, found)
+    }
 }
 
 #[derive(Copy, Clone, HeapSizeOf, PartialEq)]
diff --git a/components/script/dom/webidls/HTMLFormElement.webidl b/components/script/dom/webidls/HTMLFormElement.webidl
index a56b83235b6..fba10d25509 100644
--- a/components/script/dom/webidls/HTMLFormElement.webidl
+++ b/components/script/dom/webidls/HTMLFormElement.webidl
@@ -17,7 +17,7 @@ interface HTMLFormElement : HTMLElement {
 
   [SameObject] readonly attribute HTMLFormControlsCollection elements;
   readonly attribute unsigned long length;
-  //getter Element (unsigned long index);
+  getter Element? (unsigned long index);
   //getter (RadioNodeList or Element) (DOMString name);
 
   void submit();
diff --git a/tests/wpt/metadata/MANIFEST.json b/tests/wpt/metadata/MANIFEST.json
index cf86aac2955..b97ed7da68b 100644
--- a/tests/wpt/metadata/MANIFEST.json
+++ b/tests/wpt/metadata/MANIFEST.json
@@ -36064,6 +36064,12 @@
             "url": "/html/semantics/embedded-content/the-iframe-element/same_origin_parentage.html"
           }
         ],
+        "html/semantics/forms/the-form-element/form-indexed-element.html": [
+          {
+            "path": "html/semantics/forms/the-form-element/form-indexed-element.html",
+            "url": "/html/semantics/forms/the-form-element/form-indexed-element.html"
+          }
+        ],
         "url/url-domainToUnicode.html": [
           {
             "path": "url/url-domainToUnicode.html",
diff --git a/tests/wpt/metadata/old-tests/submission/Opera/script_scheduling/031.html.ini b/tests/wpt/metadata/old-tests/submission/Opera/script_scheduling/031.html.ini
deleted file mode 100644
index 3a3b16289bd..00000000000
--- a/tests/wpt/metadata/old-tests/submission/Opera/script_scheduling/031.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[031.html]
-  type: testharness
-  [ scheduler: focus and blur events]
-    expected: FAIL
-
diff --git a/tests/wpt/web-platform-tests/html/semantics/forms/the-form-element/form-indexed-element.html b/tests/wpt/web-platform-tests/html/semantics/forms/the-form-element/form-indexed-element.html
new file mode 100644
index 00000000000..44471aa8ca3
--- /dev/null
+++ b/tests/wpt/web-platform-tests/html/semantics/forms/the-form-element/form-indexed-element.html
@@ -0,0 +1,22 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>form.elements: indexed</title>
+<link rel="author" title="Ivan.Yang" href="mailto:jsyangwenjie@gmail.com">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<div id="test">
+<form id=form>
+<input type="radio" name="radio1" id="r1" value=1>
+<input type="radio" name="radio2" id="r2" value=2>
+</form>
+</div>
+<script>
+test(function() {
+  var form = document.getElementById("form");
+  assert_equals(form[0], document.getElementById("r1"));
+  assert_equals(form[1], document.getElementById("r2"));
+  assert_equals(form[2], undefined);
+  assert_equals(form[-1], undefined);
+  }, "form.elements should be accessed correctly by index")
+</script>