Fix bad query_x11_windows early returns (#1864)

* Fix bad early returns
* Prevent fallback tree traversal from propagation code

Signed-off-by: Tin Švagelj <tin.svagelj@live.com>

src/x11.cc

@@ -1429,39 +1429,47 @@ std::vector<Window> x11_atom_window_list(Display *display, Window window,
   return std::vector<Window>{};
 }
 
-std::vector<Window> query_x11_windows(Display *display) {
+std::vector<Window> query_x11_windows(Display *display, bool eager) {
   Window root = DefaultRootWindow(display);
 
-  Atom clients_atom = ATOM(_NET_CLIENT_LIST_STACKING);
-  std::vector<Window> result =
-      x11_atom_window_list(display, root, clients_atom);
-  if (result.empty()) { return result; }
+  std::vector<Window> result;
+
+  Atom clients_atom = XInternAtom(display, "_NET_CLIENT_LIST_STACKING", True);
+  if (clients_atom != 0) {
+    result = x11_atom_window_list(display, root, clients_atom);
+    if (!result.empty()) { return result; }
+  }
 
-  clients_atom = ATOM(_NET_CLIENT_LIST);
-  result = x11_atom_window_list(display, root, clients_atom);
-  if (result.empty()) { return result; }
+  clients_atom = XInternAtom(display, "_NET_CLIENT_LIST", True);
+  if (clients_atom != 0) {
+    result = x11_atom_window_list(display, root, clients_atom);
+    if (!result.empty()) { return result; }
+  }
 
   // slowest method
 
-  std::vector<Window> queue = {DefaultVRootWindow(display)};
-
-  Window _ignored, *children;
-  std::uint32_t count;
-
-  const auto has_wm_hints = [&](Window window) {
-    auto hints = XGetWMHints(display, window);
-    bool result = hints != NULL;
-    if (result) XFree(hints);
-    return result;
-  };
-
-  while (!queue.empty()) {
-    Window current = queue.back();
-    queue.pop_back();
-    if (XQueryTree(display, current, &_ignored, &_ignored, &children, &count)) {
-      for (size_t i = 0; i < count; i++) queue.push_back(children[i]);
-      if (has_wm_hints(current)) result.push_back(current);
-      if (count > 0) XFree(children);
+  if (eager) {
+    std::vector<Window> queue = {DefaultVRootWindow(display)};
+
+    Window _ignored, *children;
+    std::uint32_t count;
+
+    const auto has_wm_hints = [&](Window window) {
+      auto hints = XGetWMHints(display, window);
+      bool result = hints != NULL;
+      if (result) XFree(hints);
+      return result;
+    };
+
+    while (!queue.empty()) {
+      Window current = queue.back();
+      queue.pop_back();
+      if (XQueryTree(display, current, &_ignored, &_ignored, &children,
+                     &count)) {
+        for (size_t i = 0; i < count; i++) queue.push_back(children[i]);
+        if (has_wm_hints(current)) result.push_back(current);
+        if (count > 0) XFree(children);
+      }
     }
   }
 
@@ -1486,13 +1494,13 @@ Window query_x11_window_at_pos(Display *display, int x, int y) {
 
 std::vector<Window> query_x11_windows_at_pos(
     Display *display, int x, int y,
-    std::function<bool(XWindowAttributes &)> predicate) {
+    std::function<bool(XWindowAttributes &)> predicate, bool eager) {
   std::vector<Window> result;
 
   Window root = DefaultVRootWindow(display);
   XWindowAttributes attr;
 
-  for (Window current : query_x11_windows(display)) {
+  for (Window current : query_x11_windows(display, eager)) {
     int pos_x, pos_y;
     Window _ignore;
     // Doesn't account for decorations. There's no sane way to do that.

src/x11.h

@@ -132,12 +132,13 @@ std::vector<Window> x11_atom_window_list(Display *display, Window window,
 ///
 /// If neither of the atoms are provided, this function tries traversing the
 /// window graph in order to collect windows. In this case, map state of windows
-/// is ignored. This also produces a lot of noise for some WM/DEs due to
-/// inserted window decorations.
+/// is ignored.
 ///
-/// @param display which display to query for windows @return a (likely) ordered
-/// list of windows
-std::vector<Window> query_x11_windows(Display *display);
+/// @param display which display to query for windows
+/// @param eager fallback to very slow tree traversal to ensure a list of
+/// windows is returned even if window list atoms aren't defined
+/// @return a (likely) ordered list of windows
+std::vector<Window> query_x11_windows(Display *display, bool eager = false);
 
 /// @brief Finds the last ascendant of a window (trunk) before root.
 ///
@@ -171,7 +172,8 @@ Window query_x11_window_at_pos(Display *display, int x, int y);
 std::vector<Window> query_x11_windows_at_pos(
     Display *display, int x, int y,
     std::function<bool(XWindowAttributes &)> predicate =
-        [](XWindowAttributes &a) { return true; });
+        [](XWindowAttributes &a) { return true; },
+    bool eager = false);
 
 #ifdef BUILD_XDBE
 void xdbe_swap_buffers(void);