Mac a11y: Add RoleDescription and Value attributes to accessibility information.

ui/accessibility/platform/ax_platform_node_mac.mm

Index: ui/accessibility/platform/ax_platform_node_mac.mm
diff --git a/ui/accessibility/platform/ax_platform_node_mac.mm b/ui/accessibility/platform/ax_platform_node_mac.mm
index 620841889eae237edc5ee3a5a3f4f237f6de4a33..364ebee10542afd33e942bfcf2cfbd2bfda74cb8 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.mm
+++ b/ui/accessibility/platform/ax_platform_node_mac.mm
@@ -190,6 +190,11 @@ RoleMap BuildSubroleMap() {
 
 }  // namespace
 
+@interface AXPlatformNodeCocoa ()
+// Helper function for string attributes that don't require extra processing.
+- (NSString*)getStringAttribute:(ui::AXStringAttribute)attribute;
+@end
+
 @implementation AXPlatformNodeCocoa
 
 // A mapping of AX roles to native roles.
@@ -223,40 +228,10 @@ RoleMap BuildSubroleMap() {
   return gfx::ScreenRectToNSRect(node_->GetBoundsInScreen());
 }
 
-- (NSArray*)AXChildren {
-  if (!node_)
-    return nil;
-  int count = node_->GetChildCount();
-  NSMutableArray* children = [NSMutableArray arrayWithCapacity:count];
-  for (int i = 0; i < count; ++i)
-    [children addObject:node_->ChildAtIndex(i)];
-  return NSAccessibilityUnignoredChildren(children);
-}
-
-- (id)AXParent {
-  if (!node_)
-    return nil;
-  return NSAccessibilityUnignoredAncestor(node_->GetParent());
-}
-
-- (NSValue*)AXPosition {
-  return [NSValue valueWithPoint:self.boundsInScreen.origin];
-}
-
-- (NSString*)AXRole {
-  if (!node_)
-    return nil;
-  return [[self class] nativeRoleFromAXRole:node_->GetData().role];
-}
-
-- (NSValue*)AXSize {
-  return [NSValue valueWithSize:self.boundsInScreen.size];
-}
-
-- (NSString*)AXTitle {
-  std::string value;
-  if (node_->GetStringAttribute(ui::AX_ATTR_NAME, &value))
-    return base::SysUTF8ToNSString(value);
+- (NSString*)getStringAttribute:(ui::AXStringAttribute)attribute {
+  std::string attributeValue;
+  if (node_->GetStringAttribute(attribute, &attributeValue))
+    return base::SysUTF8ToNSString(attributeValue);
   return nil;
 }
 
@@ -290,6 +265,10 @@ RoleMap BuildSubroleMap() {
     // Title is required for most elements. Cocoa asks for the value even if it
     // is omitted here, but won't present it to accessibility APIs without this.
     NSAccessibilityTitleAttribute,
+
+    // Attributes which are not required, but are general to all roles.
+    NSAccessibilityRoleDescriptionAttribute,
+    NSAccessibilityValueAttribute,

[tapted, 2016/06/06 04:09:51]

So I poked around a bit - I think doing this for RoleDescriptionAttribute is
fine, but not much provides valueAttribute. we should act on that TODO below --
switch on node_->GetData().role and append extra things to the array, based on
the role.

[Patti Lor, 2016/06/10 01:36:10]

Have added switch to add Value attributes on a bunch of user input fields for
now, or do you think I should just add it for TEXT_FIELDs only and leave it?

   ];
   // TODO(tapted): Add additional attributes based on role.
 }
@@ -305,6 +284,50 @@ RoleMap BuildSubroleMap() {
   return nil;
 }
 
+// NSAccessibility attributes.
+
+- (NSArray*)AXChildren {
+  if (!node_)
+    return nil;
+  int count = node_->GetChildCount();
+  NSMutableArray* children = [NSMutableArray arrayWithCapacity:count];
+  for (int i = 0; i < count; ++i)
+    [children addObject:node_->ChildAtIndex(i)];
+  return NSAccessibilityUnignoredChildren(children);
+}
+
+- (id)AXParent {
+  if (!node_)
+    return nil;
+  return NSAccessibilityUnignoredAncestor(node_->GetParent());
+}
+
+- (NSValue*)AXPosition {
+  return [NSValue valueWithPoint:self.boundsInScreen.origin];
+}
+
+- (NSString*)AXRole {
+  if (!node_)
+    return nil;
+  return [[self class] nativeRoleFromAXRole:node_->GetData().role];
+}
+
+- (NSValue*)AXSize {
+  return [NSValue valueWithSize:self.boundsInScreen.size];
+}
+
+- (NSString*)AXTitle {
+  return [self getStringAttribute:ui::AX_ATTR_NAME];
+}
+
+- (NSString*)AXRoleDescription {
+  return [self getStringAttribute:ui::AX_ATTR_DESCRIPTION];

[tapted, 2016/06/06 04:09:51]

So if this returns nil, I think we should then try doing

NSString* role = [self AXRole];
NSString* subrole = nil;  // TODO(..): Support subroles.
return role ? NSAccessibilityRoleDescription(role, subrole) : nil;

NSAccessibilityRoleDescription gets localized descriptions for the standard
roles from AppKit.

It might be worth simply trying to pass a nil |role| as well - -maybe AppKit
provides something better than merely `nil` (or maybe it crashes - we should
check)

[Patti Lor, 2016/06/10 01:36:09]

Works with nil values! Done. Have also added the subrole attribute to this CL,
but to do this I copied some logic from browser_accessibility_cocoa.mm's subrole
method which I am not sure about.

[tapted, 2016/06/10 03:17:17]

What string does it return for nil? The API is

NSAccessibilityRoleDescription(NSString *role, NSString * __nullable subrole)

So, passing nil to subrole is unambiguously OK.

but |role| is neither __nullable nor __nonnull (nor __null_unspecified). If an
actual string is returned, then that's good, but if it returns nil, then we
can't be sure we're using the api right (and should perhaps check for that)

[Patti Lor, 2016/06/16 07:05:21]

Having a nil role returns an empty NSString, so I've left it as is.

+}
+
+- (NSString*)AXValue {
+  return [self getStringAttribute:ui::AX_ATTR_VALUE];
+}
+
 @end
 
 namespace ui {