refactor: comments, variable names

src/nvim/decoration.c

@@ -473,6 +473,8 @@ bool decor_redraw_line(win_T *wp, int row, DecorState *state)
   int const cur_end = state->current_end;
   int fut_beg = state->future_begin;
 
+  // Move future ranges to start right after current ranges.
+  // Otherwise future ranges will grow forward indefinitely.
   if (fut_beg == count) {
     fut_beg = count = cur_end;
   } else if (fut_beg != cur_end) {
@@ -528,6 +530,7 @@ static void decor_range_insert(DecorState *state, DecorRange *range)
   range->ordering = state->new_range_ordering++;
 
   int index;
+  // Get space for a new `DecorRange` from the freelist or allocate.
   if (state->free_slot_i >= 0) {
     index = state->free_slot_i;
     DecorRangeSlot *slot = &kv_A(state->slots, index);
@@ -635,11 +638,11 @@ void decor_init_draw_col(int win_col, bool hidden, DecorRange *item)
 
 void decor_recheck_draw_col(int win_col, bool hidden, DecorState *state)
 {
-  int const count = state->current_end;
+  int const end = state->current_end;
   int *const indices = state->ranges_i.items;
   DecorRangeSlot *const slots = state->slots.items;
 
-  for (int i = 0; i < count; i++) {
+  for (int i = 0; i < end; i++) {
     DecorRange *const r = &slots[indices[i]].range;
     if (r->draw_col == -3) {
       decor_init_draw_col(win_col, hidden, r);
@@ -683,6 +686,7 @@ next_mark:
   int cur_end = state->current_end;
   int fut_beg = state->future_begin;
 
+  // Promote future ranges before the cursor to active.
   for (; fut_beg < count; fut_beg++) {
     int const index = indices[fut_beg];
     DecorRange *const r = &slots[index].range;
@@ -711,7 +715,7 @@ next_mark:
     cur_end++;
   }
 
-  if (fut_beg != count) {
+  if (fut_beg < count) {
     DecorRange *r = &slots[indices[fut_beg]].range;
     if (r->start_row == row) {
       col_until = MIN(col_until, r->start_col - 1);

src/nvim/decoration.h

@@ -27,17 +27,19 @@ typedef enum {
   kDecorKindVirtText,
   kDecorKindVirtLines,
   kDecorKindUIWatched,
-} DecorRangeKind;
+} DecorRangeKindEnum;
+
+typedef uint8_t DecorRangeKind;
 
 typedef struct {
   int start_row;
   int start_col;
   int end_row;
   int end_col;
-  int ordering;
+  int ordering;  ///< range insertion order
   DecorPriority priority;
   bool owned;  ///< ephemeral decoration, free memory immediately
-  DecorRangeKind kind: 8;
+  DecorRangeKind kind;
   // next pointers MUST NOT be used, these are separate ranges
   // vt->next could be pointing to freelist memory at this point
   union {

src/nvim/drawline.c

@@ -256,11 +256,11 @@ static void draw_virt_text(win_T *wp, buf_T *buf, int col_off, int *end_col, int
   int right_pos = max_col;
   bool const do_eol = state->eol_col > -1;
 
-  int const count = state->current_end;
+  int const end = state->current_end;
   int *const indices = state->ranges_i.items;
   DecorRangeSlot *const slots = state->slots.items;
 
-  for (int i = 0; i < count; i++) {
+  for (int i = 0; i < end; i++) {
     DecorRange *item = &slots[indices[i]].range;
     if (!(item->start_row == state->row && decor_virt_pos(item))) {
       continue;
@@ -796,11 +796,11 @@ static void handle_inline_virtual_text(win_T *wp, winlinevars_T *wlv, ptrdiff_t
       wlv->virt_inline = VIRTTEXT_EMPTY;
       wlv->virt_inline_i = 0;
       DecorState *state = &decor_state;
-      int const count = state->current_end;
+      int const end = state->current_end;
       int *const indices = state->ranges_i.items;
       DecorRangeSlot *const slots = state->slots.items;
 
-      for (int i = 0; i < count; i++) {
+      for (int i = 0; i < end; i++) {
         DecorRange *item = &slots[indices[i]].range;
         if (item->draw_col == -3) {
           // No more inline virtual text before this non-inline virtual text item,