commands/move: don't flatten on move; reap empty former parent instead

Some comparisons of current Sway versus i3 behavior:

1) T[T[T[app]]] + move left
* Sway: T[app]
* i3:   T[T[app]]

2) H[V[H[V[app]]]] + move left
* Sway: H[app]
* i3:   H[V[app]]

After this commit, Sway behavior matches i3. The intermediate states
are now:

    T[T[T[app]]] -> T[T[app T[]]] -> T[T[app]]
    H[V[H[V[app]]]] -> H[V[app H[V[]]]] -> H[V[app]]

1 files changed, 8 insertions, 10 deletions

diff --git a/sway/commands/move.c b/sway/commands/move.c
index 204596c0..247c45fe 100644
--- a/sway/commands/move.c
+++ b/sway/commands/move.c
@@ -309,16 +309,6 @@ static bool container_move_in_direction(struct sway_container *container,
                 return false;
         }
 
-        // If container is in a split container by itself, move out of the split
-        if (container->parent) {
-                struct sway_container *old_parent = container->parent;
-                struct sway_container *new_parent =
-                        container_flatten(container->parent);
-                if (new_parent != old_parent) {
-                        return true;
-                }
-        }
-
         // Look for a suitable *container* sibling or parent.
         // The below loop stops once we hit the workspace because current->parent
         // is NULL for the topmost containers in a workspace.
@@ -721,12 +711,20 @@ static struct cmd_results *cmd_move_in_direction(
                 return cmd_results_new(CMD_SUCCESS, NULL);
         }
         struct sway_workspace *old_ws = container->workspace;
+        struct sway_container *old_parent = container->parent;
 
         if (!container_move_in_direction(container, direction)) {
                 // Container didn't move
                 return cmd_results_new(CMD_SUCCESS, NULL);
         }
 
+        // clean-up, destroying parents if the container was the last child
+        if (old_parent) {
+                container_reap_empty(old_parent);
+        } else if (old_ws) {
+                workspace_consider_destroy(old_ws);
+        }
+
         struct sway_workspace *new_ws = container->workspace;
 
         if (root->fullscreen_global) {