Allow focus child/parent when in fullscreen.

This is now restricted according to the already defined fullscreen
focus constraints. Test case 157 was removed, as we don't prevent
level up/down in fullscreen anymore. Those commands are properly
tested in fullscreen by test case 156.

Fixes: #612

src/commands.c

@@ -1213,23 +1213,26 @@ void cmd_focus_window_mode(I3_CMD, char *window_mode) {
  *
  */
 void cmd_focus_level(I3_CMD, char *level) {
-    if (focused &&
-        focused->type != CT_WORKSPACE &&
-        focused->fullscreen_mode != CF_NONE) {
-        LOG("Cannot change focus while in fullscreen mode.\n");
-        ysuccess(false);
-        return;
+    DLOG("level = %s\n", level);
+    bool success = false;
+
+    /* Focusing the parent can only be allowed if the newly
+     * focused container won't escape the fullscreen container. */
+    if (strcmp(level, "parent") == 0) {
+        if (focused && focused->parent) {
+            if (con_fullscreen_permits_focusing(focused->parent))
+                success = level_up();
+            else
+                LOG("Currently in fullscreen, not going up\n");
+        }
     }
 
-    DLOG("level = %s\n", level);
+    /* Focusing a child should always be allowed. */
+    else success = level_down();
 
-    if (strcmp(level, "parent") == 0)
-        level_up();
-    else level_down();
-
-    cmd_output->needs_tree_render = true;
+    cmd_output->needs_tree_render = success;
     // XXX: default reply for now, make this a better reply
-    ysuccess(true);
+    ysuccess(success);
 }
 
 /*

src/con.c

@@ -1170,6 +1170,10 @@ bool con_fullscreen_permits_focusing(Con *con) {
     if (fs->type == CT_WORKSPACE)
         return true;
 
+    /* Allow it if the container itself is the fullscreen container. */
+    if (con == fs)
+        return true;
+
     /* If fullscreen is per-output, the focus being in a different workspace is
      * sufficient to guarantee that change won't leave fullscreen in bad shape. */
     if (fs->fullscreen_mode == CF_OUTPUT &&

src/tree.c

@@ -375,38 +375,34 @@ void tree_split(Con *con, orientation_t orientation) {
 }
 
 /*
- * Moves focus one level up.
+ * Moves focus one level up. Returns true if focus changed.
  *
  */
-void level_up(void) {
-    /* We cannot go up when we are in fullscreen mode at the moment, that would
-     * be totally not intuitive */
-    if (focused->fullscreen_mode != CF_NONE) {
-        LOG("Currently in fullscreen, not going up\n");
-        return;
-    }
+bool level_up(void) {
     /* We can focus up to the workspace, but not any higher in the tree */
     if ((focused->parent->type != CT_CON &&
         focused->parent->type != CT_WORKSPACE) ||
         focused->type == CT_WORKSPACE) {
         LOG("Cannot go up any further\n");
-        return;
+        return false;
     }
     con_focus(focused->parent);
+    return true;
 }
 
 /*
- * Moves focus one level down.
+ * Moves focus one level down. Returns true if focus changed.
  *
  */
-void level_down(void) {
+bool level_down(void) {
     /* Go down the focus stack of the current node */
     Con *next = TAILQ_FIRST(&(focused->focus_head));
     if (next == TAILQ_END(&(focused->focus_head))) {
         printf("cannot go down\n");
-        return;
+        return false;
     }
     con_focus(next);
+    return true;
 }
 
 static void mark_unmapped(Con *con) {