Windows: Comboboxes (Qml and QtWidgets) don't have the UIAutomation (UIA) ExpandCollapse pattern

Context

I'm using http://accessibilityinsights.io/ to make sure my QML application passes Microsoft requirements for accessibility.

There's only one error that I couldn't resolve : Qml ComboBoxes don't have the ExpandCollapse pattern.

Code to reproduce:

ComboBox {
 model: ["First", "Second", "Third"]
}

Error

Accessibility Insights says "An element of the given ControlType must support the ExpandCollapse pattern. Section 508 502.3.10" and "How to fix:"

1. Make sure the element has the appropriate ControlType property for its function.
2. If the current ControlType is correct, modify the element to support the ExpandCollapse pattern.

I did not find any related issues in the Qt bug list.

Digging deeper

I went on to examine Qt's source code and found the following file: 

qtbase\src\plugins\platforms\windows\uiautomation\qwindowsuiamainprovider.cpp

 Here's the part that was most relevant:

case UIA_ExpandCollapsePatternId:
// Menu items with submenus.
if (accessible->role() == QAccessible::MenuItem
 && accessible->childCount() > 0
 && accessible->child(0)->role() == QAccessible::PopupMenu) {
 *pRetVal = new QWindowsUiaExpandCollapseProvider(id());
}

Which means that for the ExpandCollapse pattern to work, there must be a MenuItem object (the qml combobox doesn't have that), nor a child that's a PopupMenu.

After further testing, the ExpandCollapse pattern works fine in a menu (from QWidgets), but not in qml.

I couldn't change the combobox's role (Accessible.MenuItem), as it doesn't register for some reason (perhaps because of the C++ backend)

I tried "hacking" this in qml, to see if it could work, by testing the following code:

MenuItem
{
 text: "test"
 Rectangle {
 Accessible.role: Accessible.PopupMenu
 visible:false // to make the state "collapsed" by default.
 }
}

With this fake popup menu, I have the ExpandCollapse pattern. But obviously this isn't a ComboBox.

Solution

I think the only way to resolve this issue is to change qwindowsuiamainprovider.cpp to add the ExpandCollapse pattern to ComboBoxes, and it should work for both QtWidgets and Qml.

Accessibility concerns

I don't know much about accessibility, but if someone uses the narrator and sees that it's a combobox item type (it is), then they can probably manage.

But, Microsoft is becoming super strict and not allowing any Accessibility issues.

So I think this request will come in really soon from others (I'm working directly with OEMs that need Microsoft requirements before everyone else)

Resources

While looking for bugs, I found out that anrocha could be the person to help with this!