perf(ui): reduce allocation overhead when encoding "redraw" events

Note for external UIs: Nvim can now emit multiple "redraw" event batches
before a final "flush" event is received. To retain existing behavior,
clients should make sure to update visible state at an explicit "flush"
event, not just the end of a "redraw" batch of event.

* Get rid of copy_object() blizzard in the auto-generated ui_event layer
* Special case "grid_line" by encoding screen state directly to
  msgpack events with no intermediate API events.
* Get rid of the arcane notion of referring to the screen as the "shell"
* Array and Dictionary are kvec_t:s, so define them as such.
* Allow kvec_t:s, such as Arrays and Dictionaries, to be allocated with
  a predetermined size within an arena.
* Eliminate redundant capacity checking when filling such kvec_t:s
  with values.

1 files changed, 8 insertions, 9 deletions

diff --git a/src/nvim/ui.c b/src/nvim/ui.c
index 3e715793e6..0ac7f4a55f 100644
--- a/src/nvim/ui.c
+++ b/src/nvim/ui.c
@@ -64,6 +64,8 @@ static handle_T cursor_grid_handle = DEFAULT_GRID_HANDLE;
 static bool has_mouse = false;
 static int pending_has_mouse = -1;
 
+static Array call_buf = ARRAY_DICT_INIT;
+
 #if MIN_LOG_LEVEL > LOGLVL_DBG
 # define UI_LOG(funname)
 #else
@@ -123,6 +125,12 @@ void ui_init(void)
   default_grid.handle = 1;
   msg_grid_adj.target = &default_grid;
   ui_comp_init();
+  kv_ensure_space(call_buf, 16);
+}
+
+void ui_free_all_mem(void)
+{
+  kv_destroy(call_buf);
 }
 
 void ui_builtin_start(void)
@@ -173,15 +181,6 @@ bool ui_active(void)
   return ui_count > 1;
 }
 
-void ui_event(char *name, Array args)
-{
-  bool args_consumed = false;
-  ui_call_event(name, args, &args_consumed);
-  if (!args_consumed) {
-    api_free_array(args);
-  }
-}
-
 void ui_refresh(void)
 {
   if (!ui_active()) {