refactor(sign): store 'signcolumn' width range when it is set

Problem:  Minimum and maximum signcolumn width is determined each redraw.
Solution: Determine and store 'signcolumn' range when option is set.

src/nvim/buffer_defs.h

@@ -1206,6 +1206,8 @@ struct window_S {
   int w_nrwidth;                    // width of 'number' and 'relativenumber'
                                     // column being used
   int w_scwidth;                    // width of 'signcolumn'
+  int w_minscwidth;                 // minimum width or SCL_NO/SCL_NUM
+  int w_maxscwidth;                 // maximum width or SCL_NO/SCL_NUM
 
   // === end of cached values ===
 

src/nvim/decoration.c

@@ -442,7 +442,9 @@ void decor_redraw_signs(win_T *wp, buf_T *buf, int row, SignTextAttrs sattrs[],
                         int *cul_id, int *num_id)
 {
   MarkTreeIter itr[1];
-  if (!buf->b_signs || !marktree_itr_get_overlap(buf->b_marktree, row, 0, itr)) {
+  if (!buf->b_signs
+      || wp->w_minscwidth == SCL_NO
+      || !marktree_itr_get_overlap(buf->b_marktree, row, 0, itr)) {
     return;
   }
 
@@ -471,7 +473,7 @@ void decor_redraw_signs(win_T *wp, buf_T *buf, int row, SignTextAttrs sattrs[],
   }
 
   if (kv_size(signs)) {
-    int width = (*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u') ? 1 : wp->w_scwidth;
+    int width = wp->w_minscwidth == SCL_NUM ? 1 : wp->w_scwidth;
     int idx = MIN(width, num_text) - 1;
     qsort((void *)&kv_A(signs, 0), kv_size(signs), sizeof(MTKey), sign_cmp);
 

src/nvim/drawline.c

@@ -561,7 +561,7 @@ static void handle_lnum_col(win_T *wp, winlinevars_T *wlv, int sign_num_attr, in
       && !((has_cpo_n && !wp->w_p_bri) && wp->w_skipcol > 0 && wlv->lnum == wp->w_topline)) {
     // If 'signcolumn' is set to 'number' and a sign is present in "lnum",
     // then display the sign instead of the line number.
-    if (*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u' && wlv->sattrs[0].text) {
+    if (wp->w_minscwidth == SCL_NUM && wlv->sattrs[0].text) {
       get_sign_display_info(true, wp, wlv, 0, sign_cul_attr);
     } else {
       // Draw the line number (empty space after wrapping).

src/nvim/drawscreen.c

@@ -606,7 +606,7 @@ int update_screen(void)
     }
 
     // Reset 'statuscolumn' if there is no dedicated signcolumn but it is invalid.
-    if (*wp->w_p_stc != NUL && !wp->w_buffer->b_signcols.valid && win_no_signcol(wp)) {
+    if (*wp->w_p_stc != NUL && !wp->w_buffer->b_signcols.valid && wp->w_minscwidth <= SCL_NO) {
       wp->w_nrwidth_line_count = 0;
       wp->w_valid &= ~VALID_WCOL;
       wp->w_redr_type = UPD_NOT_VALID;
@@ -619,7 +619,7 @@ int update_screen(void)
 
   FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
     // Validate b_signcols if there is no dedicated signcolumn but 'statuscolumn' is set.
-    if (*wp->w_p_stc != NUL && win_no_signcol(wp)) {
+    if (*wp->w_p_stc != NUL && wp->w_minscwidth <= SCL_NO) {
       buf_signcols(wp->w_buffer, 0);
     }
 
@@ -2632,8 +2632,7 @@ int number_width(win_T *wp)
 
   // If 'signcolumn' is set to 'number' and there is a sign to display, then
   // the minimal width for the number column is 2.
-  if (n < 2 && wp->w_buffer->b_signs_with_text
-      && (*wp->w_p_scl == 'n' && *(wp->w_p_scl + 1) == 'u')) {
+  if (n < 2 && wp->w_buffer->b_signs_with_text && wp->w_minscwidth == SCL_NUM) {
     n = 2;
   }
 

src/nvim/option.c

@@ -2245,6 +2245,7 @@ static const char *did_set_number_relativenumber(optset_T *args)
     // When 'relativenumber'/'number' is changed and 'statuscolumn' is set, reset width.
     win->w_nrwidth_line_count = 0;
   }
+  check_signcolumn(win);
   return NULL;
 }
 
@@ -4861,6 +4862,7 @@ void didset_window_options(win_T *wp, bool valid_cursor)
   parse_winhl_opt(wp);  // sets w_hl_needs_update also for w_p_winbl
   check_blending(wp);
   set_winbar_win(wp, false, valid_cursor);
+  check_signcolumn(wp);
   wp->w_grid_alloc.blending = wp->w_p_winbl > 0;
 }
 
@@ -6170,49 +6172,12 @@ bool fish_like_shell(void)
 /// buffer signs and on user configuration.
 int win_signcol_count(win_T *wp)
 {
-  return win_signcol_configured(wp);
-}
-
-/// Return true when window "wp" has no sign column.
-bool win_no_signcol(win_T *wp)
-{
-  const char *scl = wp->w_p_scl;
-  return (*scl == 'n' && (*(scl + 1) == 'o' || (*(scl + 1) == 'u'
-                                                && (wp->w_p_nu || wp->w_p_rnu))));
-}
-
-/// Return the number of requested sign columns, based on user / configuration.
-int win_signcol_configured(win_T *wp)
-{
-  const char *scl = wp->w_p_scl;
-
-  if (win_no_signcol(wp)) {
+  if (wp->w_minscwidth <= SCL_NO) {
     return 0;
   }
 
-  // yes or yes
-  if (!strncmp(scl, "yes:", 4)) {
-    // Fixed amount of columns
-    return scl[4] - '0';
-  }
-  if (*scl == 'y') {
-    return 1;
-  }
-
-  int minimum = 0, maximum = 1;
-
-  if (!strncmp(scl, "auto:", 5)) {
-    // Variable depending on a configuration
-    maximum = scl[5] - '0';
-    // auto:<NUM>-<NUM>
-    if (strlen(scl) == 8 && *(scl + 6) == '-') {
-      minimum = maximum;
-      maximum = scl[7] - '0';
-    }
-  }
-
-  int needed_signcols = buf_signcols(wp->w_buffer, maximum);
-  int ret = MAX(minimum, MIN(maximum, needed_signcols));
+  int needed_signcols = buf_signcols(wp->w_buffer, wp->w_maxscwidth);
+  int ret = MAX(wp->w_minscwidth, MIN(wp->w_maxscwidth, needed_signcols));
   assert(ret <= SIGN_SHOW_MAX);
   return ret;
 }

src/nvim/option_vars.h

@@ -947,3 +947,6 @@ enum {
 #define MAX_NUMBERWIDTH 20      // used for 'numberwidth' and 'statuscolumn'
 
 #define TABSTOP_MAX 9999
+
+#define SCL_NO  -1  // 'signcolumn' set to "no"
+#define SCL_NUM -2  // 'signcolumn' set to "number"

src/nvim/optionstr.c

@@ -388,34 +388,53 @@ static bool valid_filetype(const char *val)
   return valid_name(val, ".-_");
 }
 
-/// Handle setting 'signcolumn' for value 'val'
+/// Handle setting 'signcolumn' for value 'val'. Store minimum and maximum width.
 ///
 /// @return OK when the value is valid, FAIL otherwise
-static int check_signcolumn(char *val)
+int check_signcolumn(win_T *wp)
 {
+  char *val = wp->w_p_scl;
   if (*val == NUL) {
     return FAIL;
   }
-  // check for basic match
-  if (check_opt_strings(val, p_scl_values, false) == OK) {
-    return OK;
-  }
 
-  // check for 'auto:<NUMBER>-<NUMBER>'
-  if (strlen(val) == 8
-      && !strncmp(val, "auto:", 5)
-      && ascii_isdigit(val[5])
-      && val[6] == '-'
-      && ascii_isdigit(val[7])) {
-    int min = val[5] - '0';
-    int max = val[7] - '0';
-    if (min < 1 || max < 2 || min > 8 || max > 9 || min >= max) {
-      return FAIL;
+  if (check_opt_strings(val, p_scl_values, false) == OK) {
+    if (!strncmp(val, "no", 2)) {  // no
+      wp->w_minscwidth = wp->w_maxscwidth = SCL_NO;
+    } else if (!strncmp(val, "nu", 2) && (wp->w_p_nu || wp->w_p_rnu)) {  // number
+      wp->w_minscwidth = wp->w_maxscwidth = SCL_NUM;
+    } else if (!strncmp(val, "yes:", 4)) {  // yes:<NUM>
+      wp->w_minscwidth = wp->w_maxscwidth = val[4] - '0';
+    } else if (*val == 'y') {  // yes
+      wp->w_minscwidth = wp->w_maxscwidth = 1;
+    } else if (!strncmp(val, "auto:", 5)) {  // auto:<NUM>
+      wp->w_minscwidth = 0;
+      wp->w_maxscwidth = val[5] - '0';
+    } else {  // auto
+      wp->w_minscwidth = 0;
+      wp->w_maxscwidth = 1;
     }
     return OK;
   }
 
-  return FAIL;
+  if (strncmp(val, "auto:", 5) != 0
+      || strlen(val) != 8
+      || !ascii_isdigit(val[5])
+      || val[6] != '-'
+      || !ascii_isdigit(val[7])) {
+    return FAIL;
+  }
+
+  // auto:<NUM>-<NUM>
+  int min = val[5] - '0';
+  int max = val[7] - '0';
+  if (min < 1 || max < 2 || min > 8 || min >= max) {
+    return FAIL;
+  }
+
+  wp->w_minscwidth = min;
+  wp->w_maxscwidth = max;
+  return OK;
 }
 
 /// Check validity of options with the 'statusline' format.
@@ -2072,16 +2091,13 @@ int expand_set_showcmdloc(optexpand_T *args, int *numMatches, char ***matches)
 const char *did_set_signcolumn(optset_T *args)
 {
   win_T *win = (win_T *)args->os_win;
-  char **varp = (char **)args->os_varp;
   const char *oldval = args->os_oldval.string.data;
-  if (check_signcolumn(*varp) != OK) {
+  if (check_signcolumn(win) != OK) {
     return e_invarg;
   }
   // When changing the 'signcolumn' to or from 'number', recompute the
   // width of the number column if 'number' or 'relativenumber' is set.
-  if (((*oldval == 'n' && *(oldval + 1) == 'u')
-       || (*win->w_p_scl == 'n' && *(win->w_p_scl + 1) == 'u'))
-      && (win->w_p_nu || win->w_p_rnu)) {
+  if ((*oldval == 'n' && *(oldval + 1) == 'u') || win->w_minscwidth == SCL_NUM) {
     win->w_nrwidth_line_count = 0;
   }
   return NULL;