Bug 1838502 - Don't expose a title for labels. r=morgan

THis is what VO expects, we apparently knew that but decided it wasn't worth fixing in the past

Differential Revision: https://phabricator.services.mozilla.com/D244050

accessible/mac/AccessibleWrap.mm

@@ -307,6 +307,9 @@ Class a11y::GetTypeFromRole(roles::Role aRole) {
     case roles::OUTLINEITEM:
       return [mozOutlineRowAccessible class];
 
+    case roles::LABEL:
+      return [MOXLabelAccessible class];
+
     default:
       return [mozAccessible class];
   }

accessible/mac/mozAccessible.mm

@@ -887,22 +887,19 @@ struct RoleDescrComparator {
                                  : nullptr;
   if (maybeRoot && maybeRoot->IsRoot() &&
       [[self moxDOMIdentifier] isEqualToString:@"a11y-announcement"]) {
-    // Our actual announcement should be stored as a child of the alert,
-    // so we verify a child exists, and then query that child below.
-    NSArray* children = [self moxChildren];
-    MOZ_ASSERT([children count] == 1 && children[0],
-               "A11yUtil event received, but no announcement found?");
-
-    mozAccessible* announcement = children[0];
-    NSString* key;
-    if ([announcement providesLabelNotTitle]) {
-      key = [announcement moxLabel];
+    nsAutoString name;
+    // Our actual announcement should be stored as a child of the alert.
+    if (Accessible* announcement = mGeckoAccessible->FirstChild()) {
+      announcement->Name(name);
     } else {
-      key = [announcement moxTitle];
+      MOZ_ASSERT_UNREACHABLE(
+          "A11yUtil event received, but no announcement found?");
     }
 
     NSDictionary* info = @{
-      NSAccessibilityAnnouncementKey : key ? key : @(""),
+      NSAccessibilityAnnouncementKey : name.IsEmpty()
+          ? @("")
+          : nsCocoaUtils::ToNSString(name),
       // High priority means VO will stop what it is currently speaking
       // to speak our announcement.
       NSAccessibilityPriorityKey : @(NSAccessibilityPriorityHigh)

accessible/mac/mozHTMLAccessible.h

@@ -42,3 +42,10 @@
 - (NSString*)moxTitle;
 
 @end
+
+@interface MOXLabelAccessible : mozAccessible
+
+// override
+- (NSString*)moxTitle;
+
+@end

accessible/mac/mozHTMLAccessible.mm

@@ -81,3 +81,11 @@ using namespace mozilla::a11y;
 }
 
 @end
+
+@implementation MOXLabelAccessible
+
+- (NSString*)moxTitle {
+  return @"";
+}
+
+@end

accessible/tests/browser/mac/browser_label_title.js

@@ -22,8 +22,8 @@ addAccessibleTask(
     let n1 = getNativeInterface(accDoc, "n1");
     let n1Label = n1.getAttributeValue("AXTitleUIElement");
     // XXX: In Safari the label is an AXText with an AXValue,
-    // here it is an AXGroup witth an AXTitle
-    is(n1Label.getAttributeValue("AXTitle"), "Label");
+    // we emulate that so VoiceOver does not speak the label twice.
+    is(n1Label.getAttributeValue("AXTitle"), "");
 
     let n2 = getNativeInterface(accDoc, "n2");
     is(n2.getAttributeValue("AXDescription"), "Two Labels");