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, 14 insertions, 0 deletions

diff --git a/src/nvim/api/private/helpers.h b/src/nvim/api/private/helpers.h
index 8423db4970..a4348d8b44 100644
--- a/src/nvim/api/private/helpers.h
+++ b/src/nvim/api/private/helpers.h
@@ -63,17 +63,31 @@
 #define PUT(dict, k, v) \
   kv_push(dict, ((KeyValuePair) { .key = cstr_to_string(k), .value = v }))
 
+#define PUT_C(dict, k, v) \
+  kv_push_c(dict, ((KeyValuePair) { .key = cstr_as_string(k), .value = v }))
+
 #define PUT_BOOL(dict, name, condition) PUT(dict, name, BOOLEAN_OBJ(condition));
 
 #define ADD(array, item) \
   kv_push(array, item)
 
+#define ADD_C(array, item) \
+  kv_push_c(array, item)
+
 #define FIXED_TEMP_ARRAY(name, fixsize) \
   Array name = ARRAY_DICT_INIT; \
   Object name##__items[fixsize]; \
   name.size = fixsize; \
   name.items = name##__items; \
 
+#define MAXSIZE_TEMP_ARRAY(name, maxsize) \
+  Array name = ARRAY_DICT_INIT; \
+  Object name##__items[maxsize]; \
+  name.capacity = maxsize; \
+  name.items = name##__items; \
+
+#define cbuf_as_string(d, s) ((String) { .data = d, .size = s })
+
 #define STATIC_CSTR_AS_STRING(s) ((String) { .data = s, .size = sizeof(s) - 1 })
 
 /// Create a new String instance, putting data in allocated memory