Bug 1895551 - Remove aria attribute from ElementInternals when set to null. r=Jamie,dom-core,edgar

Differential Revision: https://phabricator.services.mozilla.com/D209721

accessible/tests/mochitest/test_custom_element_accessibility_defaults.html

@@ -213,6 +213,13 @@ async function runTest() {
   await attributeChanged;
   testAttrs("default-sort", {"sort": "descending"}, true);
 
+  info("Changing ElementInternals ariaValueText");
+  let valueTextChanged = waitForEvent(EVENT_TEXT_VALUE_CHANGE, "default-value");
+  let valueElement = document.getElementById("default-value");
+  valueElement.internals.ariaValueText = null;
+  await valueTextChanged;
+  testValue("default-value", "5", 5, 1, 10, 0);
+
   SimpleTest.finish();
 }
 

dom/html/ElementInternals.cpp

@@ -451,9 +451,17 @@ nsresult ElementInternals::SetAttr(nsAtom* aName, const nsAString& aValue) {
   MutationObservers::NotifyARIAAttributeDefaultWillChange(mTarget, aName,
                                                           modType);
 
-  bool attrHadValue;
   nsAttrValue attrValue(aValue);
-  nsresult rs = mAttrs.SetAndSwapAttr(aName, attrValue, &attrHadValue);
+  nsresult rs = NS_OK;
+  if (DOMStringIsNull(aValue)) {
+    auto attrPos = mAttrs.IndexOfAttr(aName);
+    if (attrPos >= 0) {
+      rs = mAttrs.RemoveAttrAt(attrPos, attrValue);
+    }
+  } else {
+    bool attrHadValue = false;
+    rs = mAttrs.SetAndSwapAttr(aName, attrValue, &attrHadValue);
+  }
   nsMutationGuard::DidMutate();
 
   MutationObservers::NotifyARIAAttributeDefaultChanged(mTarget, aName, modType);