introduce workspace_squash

workspace_squash is container_flatten in the reverse
direction. Instead of eliminating redundant splits that are
parents of the target container, it eliminates pairs of
redundant H/V splits that are children of the workspace.

Splits are redundant if a con and its grandchild have the
same layout, and the immediate child has the opposite split.

For example, layouts are transformed like:

    H[V[H[app1 app2]] app3] -> H[app1 app2 app3]

i3 uses this operation to simplify the tree after moving
heavily nested containers to a higher level in the tree via
an orthogonal move.

2 files changed, 28 insertions, 0 deletions

diff --git a/include/sway/tree/container.h b/include/sway/tree/container.h
index c9290108..7e9df59f 100644
--- a/include/sway/tree/container.h
+++ b/include/sway/tree/container.h
@@ -374,4 +374,17 @@ bool container_is_sticky(struct sway_container *con);
 
 bool container_is_sticky_or_child(struct sway_container *con);
 
+/**
+ * This will destroy pairs of redundant H/V splits
+ * e.g. H[V[H[app app]] app] -> H[app app app]
+ * The middle "V[H[" are eliminated by a call to container_squash
+ * on the V[ con. It's grandchildren are added to it's parent.
+ *
+ * This function is roughly equivalent to i3's tree_flatten here:
+ * https://github.com/i3/i3/blob/1f0c628cde40cf87371481041b7197344e0417c6/src/tree.c#L651
+ *
+ * Returns the number of new containers added to the parent
+ */
+int container_squash(struct sway_container *con);
+
 #endif
diff --git a/include/sway/tree/workspace.h b/include/sway/tree/workspace.h
index 3c9f93ed..fdd92f64 100644
--- a/include/sway/tree/workspace.h
+++ b/include/sway/tree/workspace.h
@@ -116,6 +116,13 @@ struct sway_container *workspace_add_tiling(struct sway_workspace *workspace,
 void workspace_add_floating(struct sway_workspace *workspace,
 		struct sway_container *con);
 
+/**
+ * Adds a tiling container to the workspace without considering
+ * the workspace_layout, so the con will not be split.
+ */
+void workspace_insert_tiling_direct(struct sway_workspace *workspace,
+		struct sway_container *con, int index);
+
 struct sway_container *workspace_insert_tiling(struct sway_workspace *workspace,
 		struct sway_container *con, int index);
 
@@ -134,4 +141,12 @@ size_t workspace_num_tiling_views(struct sway_workspace *ws);
 
 size_t workspace_num_sticky_containers(struct sway_workspace *ws);
 
+/**
+ * workspace_squash is container_flatten in the reverse
+ * direction. Instead of eliminating redundant splits that are
+ * parents of the target container, it eliminates pairs of
+ * redundant H/V splits that are children of the workspace.
+ */
+void workspace_squash(struct sway_workspace *workspace);
+
 #endif