perf(column): only build fold/sign column when present in 'statuscolumn'

Problem:    The fold and sign column is built and stored regardless of
            whether the corresponding item is present in 'statuscolumn'.
Solution:   Since the 'statuscolumn' parses itself, we can defer
            building the columns until the corresponding item is
            actually encountered.

src/nvim/buffer_defs.h

@@ -18,6 +18,7 @@ typedef struct {
 #include "klib/kvec.h"
 #include "nvim/api/private/defs.h"
 #include "nvim/eval/typval.h"
+#include "nvim/fold_defs.h"
 #include "nvim/garray.h"
 #include "nvim/grid_defs.h"
 #include "nvim/hashtab.h"
@@ -1423,17 +1424,17 @@ struct statuscol {
   int width;                           ///< width of the status column
   int cur_attr;                        ///< current attributes in text
   int num_attr;                        ///< attributes used for line number
-  int fold_attr;                       ///< attributes used for fold column
-  int sign_attr[SIGN_SHOW_MAX + 1];    ///< attributes used for signs
+  int sign_cul_attr;                   ///< cursorline sign attr
   int truncate;                        ///< truncated width
-  bool draw;                           ///< draw statuscolumn or not
-  char fold_text[9 * 4 + 1];           ///< text in fold column (%C)
-  char *sign_text[SIGN_SHOW_MAX + 1];  ///< text in sign column (%s)
+  bool draw;                           ///< whether to draw the statuscolumn
+  bool use_cul;                        ///< whether to use cursorline attrs
   char text[MAXPATHL];                 ///< text in status column
   char *textp;                         ///< current position in text
   char *text_end;                      ///< end of text (the NUL byte)
   stl_hlrec_t *hlrec;                  ///< highlight groups
   stl_hlrec_t *hlrecp;                 ///< current highlight group
+  foldinfo_T foldinfo;                 ///< fold information
+  SignTextAttrs *sattrs;               ///< sign attributes
 };
 
 /// Macros defined in Vim, but not in Neovim

src/nvim/drawline.c

@@ -404,37 +404,10 @@ static int get_sign_attrs(buf_T *buf, linenr_T lnum, SignTextAttrs *sattrs, int
 /// the start of the buffer line "lnum" and once for the wrapped lines.
 ///
 /// @param[out] stcp  Status column attributes
-static void get_statuscol_str(win_T *wp, linenr_T lnum, int row, int startrow, int filler_lines,
-                              int cul_attr, int sign_num_attr, int sign_cul_attr, statuscol_T *stcp,
-                              foldinfo_T foldinfo, SignTextAttrs *sattrs)
+static void get_statuscol_str(win_T *wp, linenr_T lnum, int virtnum, statuscol_T *stcp)
 {
-  long relnum = -1;
-  bool use_cul = use_cursor_line_sign(wp, lnum);
-  int virtnum = row - startrow - filler_lines;
-
-  // When called the first time for line "lnum" set num_attr
-  if (stcp->num_attr == 0) {
-    stcp->num_attr = sign_num_attr ? sign_num_attr
-                     : get_line_number_attr(wp, lnum, row, startrow, filler_lines);
-  }
-  // When called for the first non-filler row of line "lnum" set num v:vars and fold column
-  if (virtnum == 0) {
-    relnum = labs(get_cursor_rel_lnum(wp, lnum));
-    if (compute_foldcolumn(wp, 0)) {
-      size_t n = fill_foldcolumn(stcp->fold_text, wp, foldinfo, lnum);
-      stcp->fold_text[n] = NUL;
-      stcp->fold_attr = win_hl_attr(wp, use_cul ? HLF_CLF : HLF_FC);
-    }
-  }
-  // Make sure to clear->set->clear sign column for filler->first->wrapped lines
-  int i = 0;
-  for (; i < wp->w_scwidth; i++) {
-    SignTextAttrs *sattr = virtnum ? NULL : sign_get_attr(i, sattrs, wp->w_scwidth);
-    stcp->sign_text[i] = sattr && sattr->text ? sattr->text : "  ";
-    stcp->sign_attr[i] = sattr ? (use_cul && sign_cul_attr ? sign_cul_attr : sattr->hl_attr_id)
-                               : win_hl_attr(wp, use_cul ? HLF_CLS : HLF_SC);
-  }
-  stcp->sign_text[i] = NULL;
+  // When called for the first non-filler row of line "lnum" set num v:vars
+  long relnum = virtnum == 0 ? labs(get_cursor_rel_lnum(wp, lnum)) : -1;
 
   // When a buffer's line count has changed, make a best estimate for the full
   // width of the status column by building with "w_nrwidth_line_count". Add
@@ -496,8 +469,7 @@ static void get_statuscol_display_info(statuscol_T *stcp, LineDrawState *draw_st
     if (stcp->textp + *n_extrap < stcp->text_end) {
       int hl = stcp->hlrecp->userhl;
       stcp->textp = stcp->hlrecp->start;
-      stcp->cur_attr = hl < 0 ? syn_id2attr(-stcp->hlrecp->userhl)
-                              : hl > 0 ? hl : stcp->num_attr;
+      stcp->cur_attr = hl < 0 ? syn_id2attr(-hl) : hl > 0 ? hl : stcp->num_attr;
       stcp->hlrecp++;
       *draw_state = WL_STC - 1;
     }
@@ -1211,7 +1183,13 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
   if (*wp->w_p_stc != NUL) {
     // Draw the 'statuscolumn' if option is set.
     statuscol.draw = true;
+    statuscol.sattrs = sattrs;
+    statuscol.foldinfo = foldinfo;
     statuscol.width = win_col_off(wp);
+    statuscol.use_cul = use_cursor_line_sign(wp, lnum);
+    statuscol.sign_cul_attr = statuscol.use_cul ? sign_cul_attr : 0;
+    statuscol.num_attr = sign_num_attr ? sign_num_attr
+                         : get_line_number_attr(wp, lnum, row, startrow, filler_lines);
   }
 
   int sign_idx = 0;
@@ -1357,8 +1335,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
         // Draw the 'statuscolumn' if option is set.
         if (statuscol.draw) {
           if (statuscol.textp == NULL) {
-            get_statuscol_str(wp, lnum, row, startrow, filler_lines, cul_attr,
-                              sign_num_attr, sign_cul_attr, &statuscol, foldinfo, sattrs);
+            get_statuscol_str(wp, lnum, row - startrow - filler_lines, &statuscol);
             if (wp->w_redr_statuscol) {
               break;
             }

src/nvim/fold.h

@@ -9,17 +9,6 @@
 #include "nvim/pos.h"
 #include "nvim/types.h"
 
-// Info used to pass info about a fold from the fold-detection code to the
-// code that displays the foldcolumn.
-typedef struct foldinfo {
-  linenr_T fi_lnum;             // line number where fold starts
-  int fi_level;                 // level of the fold; when this is zero the
-                                // other fields are invalid
-  int fi_low_level;             // lowest fold level that starts in the same
-                                // line
-  linenr_T fi_lines;
-} foldinfo_T;
-
 EXTERN int disable_fold_update INIT(= 0);
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS

src/nvim/fold_defs.h

@@ -0,0 +1,17 @@
+#ifndef NVIM_FOLD_DEFS_H
+#define NVIM_FOLD_DEFS_H
+
+#include "nvim/pos.h"
+
+// Info used to pass info about a fold from the fold-detection code to the
+// code that displays the foldcolumn.
+typedef struct foldinfo {
+  linenr_T fi_lnum;             // line number where fold starts
+  int fi_level;                 // level of the fold; when this is zero the
+                                // other fields are invalid
+  int fi_low_level;             // lowest fold level that starts in the same
+                                // line
+  linenr_T fi_lines;
+} foldinfo_T;
+
+#endif  // NVIM_FOLD_DEFS_H

src/nvim/statusline.c

@@ -38,7 +38,7 @@
 #include "nvim/path.h"
 #include "nvim/pos.h"
 #include "nvim/screen.h"
-#include "nvim/sign_defs.h"
+#include "nvim/sign.h"
 #include "nvim/statusline.h"
 #include "nvim/strings.h"
 #include "nvim/types.h"
@@ -1648,20 +1648,40 @@ int build_stl_str_hl(win_T *wp, char *out, size_t outlen, char *fmt, char *opt_n
       if (stcp == NULL) {
         break;
       }
-
       bool fold = opt == STL_FOLDCOL;
+      int width = fold ? (compute_foldcolumn(wp, 0) > 0) : wp->w_scwidth;
+
+      if (width == 0) {
+        break;
+      }
+
+      char *p;
+      if (fold) {
+        size_t n = fill_foldcolumn(out_p, wp, stcp->foldinfo, (linenr_T)get_vim_var_nr(VV_LNUM));
+        stl_items[curitem].minwid = win_hl_attr(wp, stcp->use_cul ? HLF_CLF : HLF_FC);
+        p = out_p;
+        p[n] = NUL;
+      }
+
       *buf_tmp = NUL;
-      for (int i = 0; i <= SIGN_SHOW_MAX; i++) {
-        char *p = fold ? stcp->fold_text : stcp->sign_text[i];
-        if ((!p || !*p) && *buf_tmp == NUL) {
-          break;
+      varnumber_T virtnum = get_vim_var_nr(VV_VIRTNUM);
+      for (int i = 0; i <= width; i++) {
+        if (i == width) {
+          if (*buf_tmp == NUL) {
+            break;
+          }
+          stl_items[curitem].minwid = 0;
+        } else if (!fold) {
+          SignTextAttrs *sattr = virtnum ? NULL : sign_get_attr(i, stcp->sattrs, wp->w_scwidth);
+          p = sattr && sattr->text ? sattr->text : "  ";
+          stl_items[curitem].minwid = sattr ? stcp->sign_cul_attr ? stcp->sign_cul_attr
+                                                                  : sattr->hl_attr_id
+                                            : win_hl_attr(wp, stcp->use_cul ? HLF_CLS : HLF_SC);
         }
         stl_items[curitem].type = Highlight;
         stl_items[curitem].start = out_p + strlen(buf_tmp);
-        stl_items[curitem].minwid = !p || (fold && i) ? 0 : fold ? stcp->fold_attr
-                                                                 : stcp->sign_attr[i];
         curitem++;
-        if (!p || (fold && i)) {
+        if (i == width) {
           str = buf_tmp;
           break;
         }

test/functional/ui/statuscolumn_spec.lua

@@ -456,7 +456,7 @@ describe('statuscolumn', function()
                14 aaaaa                                    |
                                                            |
     ]])
-    command('set stc=')  -- also for the default sign column
+    command('set stc=')  -- also for the default fold column
     screen:expect_unchanged()
     -- 'statuscolumn' is not too wide with custom (bogus) fold column
     command([[set stc=%{foldlevel(v:lnum)>0?repeat('-',foldlevel(v:lnum)):''}%=%l\ ]])