perf(extmarks): add metadata for efficient filtering of special decorations

This expands on the global "don't pay for what you don't use" rules for
these special extmark decorations:

- inline virtual text, which needs to be processed in plines.c when we
  calculate the size of text on screen
- virtual lines, which are needed when calculating "filler" lines
- signs, with text and/or highlights, both of which needs to be
  processed for the entire line already at the beginning of a line.

This adds a count to each node of the marktree, for how many special
marks of each kind can be found in the subtree for this node. This makes
it possible to quickly skip over these extra checks, when working in
regions of the buffer not containing these kind of marks, instead of
before where this could just be skipped if the entire _buffer_
didn't contain such marks.

src/nvim/sign.c

@@ -250,13 +250,18 @@ static int buf_delete_signs(buf_T *buf, char *group, int id, linenr_T atlnum)
 
   // When deleting the last sign need to redraw the windows to remove the
   // sign column. Not when curwin is NULL (this means we're exiting).
-  if (!buf->b_signs_with_text && curwin != NULL) {
+  if (!buf_meta_total(buf, kMTMetaSignText) && curwin != NULL) {
     changed_line_abv_curs();
   }
 
   return OK;
 }
 
+bool buf_has_signs(const buf_T *buf)
+{
+  return (buf_meta_total(buf, kMTMetaSignHL) + buf_meta_total(buf, kMTMetaSignText));
+}
+
 /// List placed signs for "rbuf".  If "rbuf" is NULL do it for all buffers.
 static void sign_list_placed(buf_T *rbuf, char *group)
 {
@@ -270,7 +275,7 @@ static void sign_list_placed(buf_T *rbuf, char *group)
   msg_putchar('\n');
 
   while (buf != NULL && !got_int) {
-    if (buf->b_signs) {
+    if (buf_has_signs(buf)) {
       vim_snprintf(lbuf, MSG_BUF_LEN, _("Signs for %s:"), buf->b_fname);
       msg_puts_attr(lbuf, HL_ATTR(HLF_D));
       msg_putchar('\n');
@@ -415,7 +420,7 @@ static int sign_define_by_name(char *name, char *icon, char *text, char *linehl,
   } else {
     // Signs may already exist, a redraw is needed in windows with a non-empty sign list.
     FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-      if (wp->w_buffer->b_signs) {
+      if (buf_has_signs(wp->w_buffer)) {
         redraw_buf_later(wp->w_buffer, UPD_NOT_VALID);
       }
     }
@@ -542,7 +547,7 @@ static int sign_place(uint32_t *id, char *group, char *name, buf_T *buf, linenr_
 
 static int sign_unplace_inner(buf_T *buf, int id, char *group, linenr_T atlnum)
 {
-  if (!buf->b_signs) {  // No signs in the buffer
+  if (!buf_has_signs(buf)) {  // No signs in the buffer
     return FAIL;
   }
 
@@ -562,7 +567,7 @@ static int sign_unplace_inner(buf_T *buf, int id, char *group, linenr_T atlnum)
   // When all the signs in a buffer are removed, force recomputing the
   // number column width (if enabled) in all the windows displaying the
   // buffer if 'signcolumn' is set to 'number' in that window.
-  if (!buf->b_signs_with_text) {
+  if (!buf_meta_total(buf, kMTMetaSignText)) {
     may_force_numberwidth_recompute(buf, true);
   }
 
@@ -962,7 +967,7 @@ static void sign_get_placed_in_buf(buf_T *buf, linenr_T lnum, int sign_id, const
   tv_dict_add_list(d, S_LEN("signs"), l);
 
   int64_t ns = group_get_ns(group);
-  if (!buf->b_signs || ns < 0) {
+  if (!buf_has_signs(buf) || ns < 0) {
     return;
   }
 
@@ -1006,7 +1011,7 @@ static void sign_get_placed(buf_T *buf, linenr_T lnum, int id, const char *group
     sign_get_placed_in_buf(buf, lnum, id, group, retlist);
   } else {
     FOR_ALL_BUFFERS(cbuf) {
-      if (cbuf->b_signs) {
+      if (buf_has_signs(cbuf)) {
         sign_get_placed_in_buf(cbuf, 0, id, group, retlist);
       }
     }