Simplify transactions by utilising a dirty flag on containers

This PR changes the way we handle transactions to a more simple method.
The new method is to mark containers as dirty from low level code
(eg. arranging, or container_destroy, and eventually seat_set_focus),
then call transaction_commit_dirty which picks up those containers and
runs them through a transaction. The old methods of using transactions
(arrange_and_commit, or creating one manually) are now no longer
possible.

The highest-level code (execute_command and view implementation
handlers) will call transaction_commit_dirty, so most other code just
needs to set containers as dirty. This is done by arranging, but can
also be done by calling container_set_dirty.

include/sway/desktop/transaction.h

@@ -6,34 +6,25 @@
 /**
  * Transactions enable us to perform atomic layout updates.
  *
- * When we want to make adjustments to the layout, we create a transaction.
- * A transaction contains a list of affected containers and their new state.
+ * A transaction contains a list of containers and their new state.
  * A state might contain a new size, or new border settings, or new parent/child
  * relationships.
  *
- * Calling transaction_commit() makes sway notify of all the affected clients
- * with their new sizes. We then wait for all the views to respond with their
- * new surface sizes. When all are ready, or when a timeout has passed, we apply
- * the updates all at the same time.
+ * Committing a transaction makes sway notify of all the affected clients with
+ * their new sizes. We then wait for all the views to respond with their new
+ * surface sizes. When all are ready, or when a timeout has passed, we apply the
+ * updates all at the same time.
+ *
+ * When we want to make adjustments to the layout, we change the pending state
+ * in containers, mark them as dirty and call transaction_commit_dirty(). This
+ * create and commits a transaction from the dirty containers.
  */
 
-struct sway_transaction;
-
 /**
- * Create a new transaction.
+ * Find all dirty containers, create and commit a transaction containing them,
+ * and unmark them as dirty.
  */
-struct sway_transaction *transaction_create(void);
-
-/**
- * Add a container's pending state to the transaction.
- */
-void transaction_add_container(struct sway_transaction *transaction,
-		struct sway_container *container);
-
-/**
- * Submit a transaction to the client views for configuration.
- */
-void transaction_commit(struct sway_transaction *transaction);
+void transaction_commit_dirty(void);
 
 /**
  * Notify the transaction system that a view is ready for the new layout.

include/sway/server.h

@@ -47,10 +47,7 @@ struct sway_server {
 	bool debug_txn_timings;
 
 	list_t *transactions;
-
-	// When a view is being destroyed and is waiting for a transaction to
-	// complete it will be stored here.
-	list_t *destroying_containers;
+	list_t *dirty_containers;
 };
 
 struct sway_server server;

include/sway/tree/arrange.h

@@ -11,26 +11,8 @@ void remove_gaps(struct sway_container *c);
 void add_gaps(struct sway_container *c);
 
 /**
- * Arrange layout for all the children of the given container, and add them to
- * the given transaction.
- *
- * Use this function if you need to arrange multiple sections of the tree in one
- * transaction.
- *
- * You must set the desired state of the container before calling
- * arrange_windows, then don't change any state-tracked properties in the
- * container until you've called transaction_commit.
+ * Arrange layout for all the children of the given container.
  */
-void arrange_windows(struct sway_container *container,
-		struct sway_transaction *transaction);
-
-/**
- * Arrange layout for the given container and commit the transaction.
- *
- * This function is a wrapper around arrange_windows, and handles creating and
- * committing the transaction for you. Use this function if you're only doing
- * one arrange operation.
- */
-void arrange_and_commit(struct sway_container *container);
+void arrange_windows(struct sway_container *container);
 
 #endif

include/sway/tree/container.h

@@ -144,6 +144,10 @@ struct sway_container {
 
 	bool destroying;
 
+	// If true, indicates that the container has pending state that differs from
+	// the current.
+	bool dirty;
+
 	struct {
 		struct wl_signal destroy;
 		// Raised after the tree updates, but before arrange_windows
@@ -303,4 +307,10 @@ void container_get_box(struct sway_container *container, struct wlr_box *box);
 void container_floating_move_to(struct sway_container *con,
 		double lx, double ly);
 
+/**
+ * Mark a container as dirty if it isn't already. Dirty containers will be
+ * included in the next transaction then unmarked as dirty.
+ */
+void container_set_dirty(struct sway_container *container);
+
 #endif