keybindings: Do a breadth first search in our keysym to keycode code

Commit 1af0033368 made a subtle change
regarding how XKeysymToKeycode behaves. It does a depth first search
while XKeysymToKeycode is documented to do a breadth first search:

"this function looks in each column of the core keyboard mapping in
turn and returns the lowest numbered key that matches in the lowest
numbered group" - from the XKB library documentation

Looping over all keycodes for each layout and level index makes us go
back to the previous behavior.

https://bugzilla.gnome.org/show_bug.cgi?id=737134

src/core/keybindings-private.h

@@ -101,6 +101,8 @@ typedef struct
   MetaKeyCombo *iso_next_group_combos;
   int n_iso_next_group_combos;
 
+  xkb_level_index_t keymap_num_levels;
+
   /* Alt+click button grabs */
   ClutterModifierType window_grab_modifiers;
 } MetaKeyBindingManager;

src/core/keybindings.c

@@ -240,29 +240,19 @@ reload_modmap (MetaKeyBindingManager *keys)
 
 static gboolean
 is_keycode_for_keysym (struct xkb_keymap *keymap,
+                       xkb_layout_index_t layout,
+                       xkb_level_index_t  level,
                        xkb_keycode_t      keycode,
                        xkb_keysym_t       keysym)
 {
-  xkb_layout_index_t num_layouts, i;
+  const xkb_keysym_t *syms;
+  int num_syms, k;
 
-  num_layouts = xkb_keymap_num_layouts_for_key (keymap, keycode);
+  num_syms = xkb_keymap_key_get_syms_by_level (keymap, keycode, layout, level, &syms);
-  for (i = 0; i < num_layouts; i++)
+  for (k = 0; k < num_syms; k++)
     {
-      xkb_level_index_t num_levels, j;
+      if (syms[k] == keysym)
-
+        return TRUE;
-      num_levels = xkb_keymap_num_levels_for_key (keymap, keycode, i);
-      for (j = 0; j < num_levels; j++)
-        {
-          const xkb_keysym_t *syms;
-          int num_syms, k;
-
-          num_syms = xkb_keymap_key_get_syms_by_level (keymap, keycode, i, j, &syms);
-          for (k = 0; k < num_syms; k++)
-            {
-              if (syms[k] == keysym)
-                return TRUE;
-            }
-        }
     }
 
   return FALSE;
@@ -272,6 +262,8 @@ typedef struct
 {
   GArray *keycodes;
   xkb_keysym_t keysym;
+  xkb_layout_index_t layout;
+  xkb_level_index_t level;
 } FindKeysymData;
 
 static void
@@ -282,8 +274,10 @@ get_keycodes_for_keysym_iter (struct xkb_keymap *keymap,
   FindKeysymData *search_data = data;
   GArray *keycodes = search_data->keycodes;
   xkb_keysym_t keysym = search_data->keysym;
+  xkb_layout_index_t layout = search_data->layout;
+  xkb_level_index_t level = search_data->level;
 
-  if (is_keycode_for_keysym (keymap, keycode, keysym))
+  if (is_keycode_for_keysym (keymap, layout, level, keycode, keysym))
     g_array_append_val (keycodes, keycode);
 }
 
@@ -311,8 +305,15 @@ get_keycodes_for_keysym (MetaKeyBindingManager  *keys,
   {
     MetaBackend *backend = meta_get_backend ();
     struct xkb_keymap *keymap = meta_backend_get_keymap (backend);
-    FindKeysymData search_data = { retval, keysym };
+    xkb_layout_index_t i;
-    xkb_keymap_key_for_each (keymap, get_keycodes_for_keysym_iter, &search_data);
+    xkb_level_index_t j;
+
+    for (i = 0; i < xkb_keymap_num_layouts (keymap); i++)
+      for (j = 0; j < keys->keymap_num_levels; j++)
+        {
+          FindKeysymData search_data = { retval, keysym, i, j };
+          xkb_keymap_key_for_each (keymap, get_keycodes_for_keysym_iter, &search_data);
+        }
   }
 
  out:
@@ -340,6 +341,32 @@ get_first_keycode_for_keysym (MetaKeyBindingManager *keys,
   return keycode;
 }
 
+static void
+determine_keymap_num_levels_iter (struct xkb_keymap *keymap,
+                                  xkb_keycode_t      keycode,
+                                  void              *data)
+{
+  xkb_level_index_t *num_levels = data;
+  xkb_layout_index_t i;
+
+  for (i = 0; i < xkb_keymap_num_layouts_for_key (keymap, keycode); i++)
+    {
+      xkb_level_index_t level = xkb_keymap_num_levels_for_key (keymap, keycode, i);
+      if (level > *num_levels)
+        *num_levels = level;
+    }
+}
+
+static void
+determine_keymap_num_levels (MetaKeyBindingManager *keys)
+{
+  MetaBackend *backend = meta_get_backend ();
+  struct xkb_keymap *keymap = meta_backend_get_keymap (backend);
+
+  keys->keymap_num_levels = 0;
+  xkb_keymap_key_for_each (keymap, determine_keymap_num_levels_iter, &keys->keymap_num_levels);
+}
+
 static void
 reload_iso_next_group_combos (MetaKeyBindingManager *keys)
 {
@@ -488,6 +515,8 @@ reload_keycodes (MetaKeyBindingManager *keys)
   meta_topic (META_DEBUG_KEYBINDINGS,
               "Reloading keycodes for binding tables\n");
 
+  determine_keymap_num_levels (keys);
+
   if (keys->overlay_key_combo.keysym != 0)
     {
       keys->overlay_key_combo.keycode =