mac: make disabled elements visible to VoiceOver

Before this change, an element with the "disabled" restriction would
disallow every accessibility selector - crucially including selectors
like "isAccessibilityElement" or "accessibilityParent", which are
required for conforming accessibility elements. This caused disabled
elements to be completely skipped by VoiceOver, which hampers uses of
them as markers of functionality that exists but is disabled and
as menu headings.

Bug: 1067760
Change-Id: If64a02223930f3e5c404415798a56738a7faed88
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536088
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828226}

ui/accessibility/platform/ax_platform_node_mac.mm

@@ -351,6 +351,12 @@ bool AlsoUseShowMenuActionForDefaultAction(const ui::AXNodeData& data) {
          data.role == ax::mojom::Role::kPopUpButton;
 }
 
+// Check whether |selector| is an accessibility setter. This is a heuristic but
+// seems to be a pretty good one.
+bool IsAXSetter(SEL selector) {
+  return [NSStringFromSelector(selector) hasPrefix:@"setAccessibility"];
+}
+
 }  // namespace
 
 @interface AXPlatformNodeCocoa (Private)
@@ -995,33 +1001,26 @@ bool AlsoUseShowMenuActionForDefaultAction(const ui::AXNodeData& data) {
   if (!_node)
     return NO;
 
-  const ax::mojom::Restriction restriction = _node->GetData().GetRestriction();
-  if (restriction == ax::mojom::Restriction::kDisabled)
-    return NO;
+  if (selector == @selector(setAccessibilityFocused:))
+    return _node->GetData().HasState(ax::mojom::State::kFocusable);
 
-  if (selector == @selector(setAccessibilityValue:)) {
+  if (selector == @selector(setAccessibilityValue:) &&
+      _node->GetData().role == ax::mojom::Role::kTab) {
     // Tabs use the radio button role on Mac, so they are selected by calling
     // setSelected on an individual tab, rather than by setting the selected
     // element on the tabstrip as a whole.
-    if (_node->GetData().role == ax::mojom::Role::kTab) {
-      return !_node->GetData().GetBoolAttribute(
-          ax::mojom::BoolAttribute::kSelected);
-    }
-    return restriction != ax::mojom::Restriction::kReadOnly;
+    return !_node->GetData().GetBoolAttribute(
+        ax::mojom::BoolAttribute::kSelected);
   }
 
+  // Don't allow calling AX setters on disabled elements.
   // TODO(https://crbug.com/692362): Once the underlying bug in
   // views::Textfield::SetSelectionRange() described in that bug is fixed,
-  // remove the check here; right now, this check serves to prevent
-  // accessibility clients from trying to set the selection range, which won't
-  // work because of 692362.
-  if (selector == @selector(setAccessibilitySelectedText:) ||
-      selector == @selector(setAccessibilitySelectedTextRange:)) {
-    return restriction != ax::mojom::Restriction::kReadOnly;
-  }
-
-  if (selector == @selector(setAccessibilityFocused:))
-    return _node->GetData().HasState(ax::mojom::State::kFocusable);
+  // remove the check here when the selector is setAccessibilitySelectedText*;
+  // right now, this check serves to prevent accessibility clients from trying
+  // to set the selection range, which won't work because of 692362.
+  if (_node->GetData().IsReadOnlyOrDisabled() && IsAXSetter(selector))
+    return NO;
 
   // TODO(https://crbug.com/386671): What about role-specific selectors?
   return [super isAccessibilitySelectorAllowed:selector];