Bug 1886371 part 1: Hook up our native UIA tree. r=nlapre,win-reviewers,rkraesig

1. Respond to WM_GETOBJECT with our IRawElementProviderSimple implementation for the root Accessible of the HWND.
2. Don't allow QueryInterface to UIA interfaces if the UIA pref is disabled. This stops WM_GETOBJECT from returning our UIA implementation in this case.
3. Specify the appropriate provider options.

Differential Revision: https://phabricator.services.mozilla.com/D205179

accessible/windows/msaa/MsaaAccessible.cpp

@@ -14,6 +14,7 @@
 #include "mozilla/a11y/AccessibleWrap.h"
 #include "mozilla/a11y/Compatibility.h"
 #include "mozilla/a11y/DocAccessibleParent.h"
+#include "mozilla/StaticPrefs_accessibility.h"
 #include "MsaaAccessible.h"
 #include "MsaaDocAccessible.h"
 #include "MsaaRootAccessible.h"
@@ -522,9 +523,11 @@ MsaaAccessible::QueryInterface(REFIID iid, void** ppv) {
     if (SUCCEEDED(hr)) {
       return hr;
     }
-    hr = uiaRawElmProvider::QueryInterface(iid, ppv);
-    if (SUCCEEDED(hr)) {
-      return hr;
+    if (StaticPrefs::accessibility_uia_enable()) {
+      hr = uiaRawElmProvider::QueryInterface(iid, ppv);
+      if (SUCCEEDED(hr)) {
+        return hr;
+      }
     }
   }
   if (*ppv) {

accessible/windows/uia/uiaRawElmProvider.cpp

@@ -113,8 +113,9 @@ uiaRawElmProvider::get_ProviderOptions(
     __RPC__out enum ProviderOptions* aOptions) {
   if (!aOptions) return E_INVALIDARG;
 
-  // This method is not used with IAccessibleEx implementations.
-  *aOptions = ProviderOptions_ServerSideProvider;
+  *aOptions = ProviderOptions_ServerSideProvider |
+              ProviderOptions_UseComThreading |
+              ProviderOptions_HasNativeIAccessible;
   return S_OK;
 }
 

toolkit/library/moz.build

@@ -59,7 +59,7 @@ def Libxul(name, output_category=None):
     ]
 
     if CONFIG["ACCESSIBILITY"]:
-        DELAYLOAD_DLLS += ["oleacc.dll"]
+        DELAYLOAD_DLLS += ["oleacc.dll", "UIAutomationCore.dll"]
 
     if CONFIG["MOZ_WEBRTC"]:
         DELAYLOAD_DLLS += ["msdmo.dll"]
@@ -381,6 +381,7 @@ if CONFIG["OS_ARCH"] == "WINNT":
     if CONFIG["ACCESSIBILITY"]:
         OS_LIBS += [
             "oleacc",
+            "uiautomationcore",
         ]
 
     # Prevent winapi-rs from statically linking

widget/windows/nsWindow.cpp

@@ -182,6 +182,7 @@
 #  endif
 #  include "mozilla/a11y/Compatibility.h"
 #  include "oleidl.h"
+#  include <uiautomation.h>
 #  include <winuser.h>
 #  include "nsAccessibilityService.h"
 #  include "mozilla/a11y/DocAccessible.h"
@@ -5886,6 +5887,19 @@ bool nsWindow::ProcessMessageInternal(UINT msg, WPARAM& wParam, LPARAM& lParam,
           a11y::LazyInstantiator::EnableBlindAggregation(mWnd);
           result = true;
         }
+      } else if (objId == UiaRootObjectId) {
+        if (a11y::LocalAccessible* acc = GetAccessible()) {
+          RefPtr<IAccessible> ia;
+          acc->GetNativeInterface(getter_AddRefs(ia));
+          MOZ_ASSERT(ia);
+          RefPtr<IRawElementProviderSimple> uia;
+          ia->QueryInterface(IID_IRawElementProviderSimple,
+                             getter_AddRefs(uia));
+          if (uia) {
+            *aRetValue = UiaReturnRawElementProvider(mWnd, wParam, lParam, uia);
+            result = true;
+          }
+        }
       }
     } break;
 #endif