Bug 1556373 - Implement labels attribute of ElementInternals; r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D126130

dom/html/ElementInternals.cpp

@@ -56,6 +56,17 @@ HTMLFormElement* ElementInternals::GetForm(ErrorResult& aRv) const {
   return GetForm();
 }
 
+// https://html.spec.whatwg.org/#dom-elementinternals-labels
+already_AddRefed<nsINodeList> ElementInternals::GetLabels(
+    ErrorResult& aRv) const {
+  if (!mTarget || !mTarget->IsFormAssociatedElement()) {
+    aRv.ThrowNotSupportedError(
+        "Target element is not a form-associated custom element");
+    return nullptr;
+  }
+  return mTarget->Labels();
+}
+
 void ElementInternals::SetForm(HTMLFormElement* aForm) { mForm = aForm; }
 
 void ElementInternals::ClearForm(bool aRemoveFromForm, bool aUnbindOrDelete) {

dom/html/ElementInternals.h

@@ -12,6 +12,8 @@
 #include "nsIFormControl.h"
 #include "nsWrapperCache.h"
 
+class nsINodeList;
+
 namespace mozilla {
 
 class ErrorResult;
@@ -38,6 +40,7 @@ class ElementInternals final : public nsIFormControl, public nsWrapperCache {
   // WebIDL
   ShadowRoot* GetShadowRoot() const;
   mozilla::dom::HTMLFormElement* GetForm(ErrorResult& aRv) const;
+  already_AddRefed<nsINodeList> GetLabels(ErrorResult& aRv) const;
 
   // nsIFormControl
   mozilla::dom::HTMLFieldSetElement* GetFieldSet() override {

dom/html/HTMLElement.h

@@ -26,6 +26,7 @@ class HTMLElement final : public nsGenericHTMLFormElement {
   // Element
   void SetCustomElementDefinition(
       CustomElementDefinition* aDefinition) override;
+  bool IsLabelable() const override { return IsFormAssociatedElement(); }
 
   // nsGenericHTMLElement
   // https://html.spec.whatwg.org/multipage/custom-elements.html#dom-attachinternals

dom/webidl/ElementInternals.webidl

@@ -15,4 +15,7 @@ interface ElementInternals {
   // Form-associated custom elements
   [Pref="dom.webcomponents.formAssociatedCustomElement.enabled", Throws]
   readonly attribute HTMLFormElement? form;
+
+  [Pref="dom.webcomponents.formAssociatedCustomElement.enabled", Throws]
+  readonly attribute NodeList labels;
 };

testing/web-platform/meta/custom-elements/form-associated/ElementInternals-labels.html.ini

@@ -1,7 +0,0 @@
-[ElementInternals-labels.html]
-  [LABEL click]
-    expected: FAIL
-
-  [LABEL association]
-    expected: FAIL
-

testing/web-platform/meta/html/dom/idlharness.https.html.ini

@@ -295,7 +295,8 @@ prefs: [dom.security.featurePolicy.experimental.enabled:true, dom.security.featu
     expected: FAIL
 
   [ElementInternals interface: attribute labels]
-    expected: FAIL
+    expected:
+      if release_or_beta: FAIL
 
   [AudioTrack interface: attribute id]
     expected: FAIL

testing/web-platform/tests/custom-elements/form-associated/ElementInternals-labels.html

@@ -36,6 +36,10 @@ test(() => {
   const labels = container.querySelectorAll('label');
   control = container.querySelector('my-control');
   assert_array_equals(control.i.labels, labels);
+
+  container.innerHTML = '<my-control></my-control>';
+  control = container.querySelector('my-control');
+  assert_array_equals(control.i.labels, []);
 }, 'LABEL association');
 
 test(() => {
@@ -46,5 +50,14 @@ test(() => {
   container.querySelector('label').click();
   assert_equals(clickCount, 1);
 }, 'LABEL click');
+
+test(() => {
+  class NotFormAssociatedElement extends HTMLElement {}
+  customElements.define('not-form-associated-element', NotFormAssociatedElement);
+  const element = new NotFormAssociatedElement();
+  const i = element.attachInternals();
+  assert_throws_dom('NotSupportedError', () => i.labels);
+}, "ElementInternals.labels should throw NotSupportedError if the target element is not a form-associated custom element");
+
 </script>
 </body>