user32: Don't allow activating a WS_CHILD top-level window through SetFocus.

dlls/user32/focus.c

@@ -266,7 +266,11 @@ HWND WINAPI SetFocus( HWND hwnd )
             LONG style = GetWindowLongW( hwndTop, GWL_STYLE );
             if (style & (WS_MINIMIZE | WS_DISABLED)) return 0;
             parent = GetAncestor( hwndTop, GA_PARENT );
-            if (!parent || parent == GetDesktopWindow()) break;
+            if (!parent || parent == GetDesktopWindow())
+            {
+                if ((style & (WS_POPUP|WS_CHILD)) == WS_CHILD) return 0;
+                break;
+            }
             if (parent == get_hwnd_message_parent()) return 0;
             hwndTop = parent;
         }

dlls/user32/tests/win.c

@@ -2513,7 +2513,7 @@ static LRESULT WINAPI set_focus_on_activate_proc(HWND hwnd, UINT msg, WPARAM wp,
 
 static void test_SetFocus(HWND hwnd)
 {
-    HWND child, child2;
+    HWND child, child2, ret;
     WNDPROC old_wnd_proc;
 
     /* check if we can set focus to non-visible windows */
@@ -2588,9 +2588,32 @@ todo_wine
     ok( GetActiveWindow() == hwnd, "parent window %p should be active\n", hwnd);
 todo_wine
     ok( GetFocus() == child, "Focus should be on child %p, not %p\n", child, GetFocus() );
-
     SetWindowLongPtr(hwnd, GWLP_WNDPROC, (LONG_PTR)old_wnd_proc);
 
+    SetFocus( hwnd );
+    SetParent( child, GetDesktopWindow());
+    SetParent( child2, child );
+    ok( GetActiveWindow() == hwnd, "parent window %p should be active\n", hwnd);
+    ok( GetFocus() == hwnd, "Focus should be on parent %p\n", hwnd );
+    ret = SetFocus( child2 );
+    ok( ret == 0, "SetFocus %p should fail\n", child2);
+    ok( GetActiveWindow() == hwnd, "parent window %p should be active\n", hwnd);
+    ok( GetFocus() == hwnd, "Focus should be on parent %p\n", hwnd );
+    ret = SetFocus( child );
+    ok( ret == 0, "SetFocus %p should fail\n", child);
+    ok( GetActiveWindow() == hwnd, "parent window %p should be active\n", hwnd);
+    ok( GetFocus() == hwnd, "Focus should be on parent %p\n", hwnd );
+    SetWindowLongW( child, GWL_STYLE, WS_POPUP|WS_CHILD );
+    SetFocus( child2 );
+    ok( GetActiveWindow() == child, "child window %p should be active\n", child);
+    ok( GetFocus() == child2, "Focus should be on child2 %p\n", child2 );
+    SetFocus( hwnd );
+    ok( GetActiveWindow() == hwnd, "parent window %p should be active\n", hwnd);
+    ok( GetFocus() == hwnd, "Focus should be on parent %p\n", hwnd );
+    SetFocus( child );
+    ok( GetActiveWindow() == child, "child window %p should be active\n", child);
+    ok( GetFocus() == child, "Focus should be on child %p\n", child );
+
     DestroyWindow( child2 );
     DestroyWindow( child );
 }