Merge pull request #7611 from electron/only-enable-msaa-if-needed

Check harder before enabling Accessibility support on Win32

atom/browser/native_window_views.cc

@@ -138,7 +138,7 @@ NativeWindowViews::NativeWindowViews(
       menu_bar_visible_(false),
       menu_bar_alt_pressed_(false),
 #if defined(OS_WIN)
-      enabled_a11y_support_(false),
+      checked_for_a11y_support_(false),
       thick_frame_(true),
 #endif
       keyboard_event_handler_(new views::UnhandledKeyboardEventHandler),

atom/browser/native_window_views.h

@@ -18,6 +18,8 @@
 #include "atom/browser/ui/win/message_handler_delegate.h"
 #include "atom/browser/ui/win/taskbar_host.h"
 #include "base/win/scoped_gdi_object.h"
+#include "ui/base/win/accessibility_misc_utils.h"
+#include <UIAutomationCoreApi.h>
 #endif
 
 namespace views {
@@ -228,8 +230,8 @@ class NativeWindowViews : public NativeWindow,
   // In charge of running taskbar related APIs.
   TaskbarHost taskbar_host_;
 
-  // If true we have enabled a11y
-  bool enabled_a11y_support_;
+  // Memoized version of a11y check
+  bool checked_for_a11y_support_;
 
   // Whether to show the WS_THICKFRAME style.
   bool thick_frame_;

atom/browser/native_window_views_win.cc

@@ -92,15 +92,24 @@ bool NativeWindowViews::PreHandleMSG(
     // accessibility object.
     case WM_GETOBJECT: {
       const DWORD obj_id = static_cast<DWORD>(l_param);
-      if (enabled_a11y_support_) return false;
 
-      if (obj_id == OBJID_CLIENT) {
-        const auto axState = content::BrowserAccessibilityState::GetInstance();
-        if (axState && !axState->IsAccessibleBrowser()) {
-          axState->OnScreenReaderDetected();
-          enabled_a11y_support_ = true;
-          Browser::Get()->OnAccessibilitySupportChanged();
-        }
+      if (obj_id != OBJID_CLIENT) {
+        return false;
+      }
+
+      if (checked_for_a11y_support_) return false;
+      checked_for_a11y_support_ = true;
+
+      UINT screenReader = 0;
+      SystemParametersInfo(SPI_GETSCREENREADER, 0, &screenReader, 0);
+      if (!screenReader || !UiaClientsAreListening()) {
+        return false;
+      }
+
+      const auto axState = content::BrowserAccessibilityState::GetInstance();
+      if (axState && !axState->IsAccessibleBrowser()) {
+        axState->OnScreenReaderDetected();
+        Browser::Get()->OnAccessibilitySupportChanged();
       }
 
       return false;

electron.gyp

@@ -281,6 +281,7 @@
               '-lwininet.lib',
               '-lwinmm.lib',
               '-lcrypt32.lib',
+              '-luiautomationcore.lib',
             ],
           },
           'dependencies': [