refactor(column): define and use maximum 'statuscolumn' width

Problem:  The maximum 'statuscolumn' width and grow behavior is undocumented.
Solution: Define, use and document the maximum 'statuscolumn' width and grow behavior.

5 files changed, 18 insertions, 20 deletions

diff --git a/src/nvim/drawline.c b/src/nvim/drawline.c
index dbcd4ace8c..22eb0b9c31 100644
--- a/src/nvim/drawline.c
+++ b/src/nvim/drawline.c
@@ -563,9 +563,6 @@ static void draw_lnum_col(win_T *wp, winlinevars_T *wlv, int sign_num_attr, int
 }
 
 /// Build and draw the 'statuscolumn' string for line "lnum" in window "wp".
-/// Fill "stcp" with the built status column string and attributes.
-///
-/// @param[out] stcp  Status column attributes
 static void draw_statuscol(win_T *wp, winlinevars_T *wlv, linenr_T lnum, int virtnum,
                            statuscol_T *stcp)
 {
@@ -579,11 +576,9 @@ static void draw_statuscol(win_T *wp, winlinevars_T *wlv, linenr_T lnum, int vir
   if (wp->w_statuscol_line_count != wp->w_nrwidth_line_count) {
     wp->w_statuscol_line_count = wp->w_nrwidth_line_count;
     set_vim_var_nr(VV_VIRTNUM, 0);
-    build_statuscol_str(wp, wp->w_nrwidth_line_count, 0, buf, stcp);
-    if (stcp->truncate > 0) {
-      // Add truncated width to avoid unnecessary redraws
-      int addwidth = MIN(stcp->truncate, MAX_NUMBERWIDTH - wp->w_nrwidth);
-      stcp->truncate = 0;
+    int width = build_statuscol_str(wp, wp->w_nrwidth_line_count, 0, buf, stcp);
+    if (width > stcp->width) {
+      int addwidth = MIN(width - stcp->width, MAX_STCWIDTH - stcp->width);
       stcp->width += addwidth;
       wp->w_nrwidth += addwidth;
       wp->w_nrwidth_width = wp->w_nrwidth;
@@ -594,13 +589,13 @@ static void draw_statuscol(win_T *wp, winlinevars_T *wlv, linenr_T lnum, int vir
 
   int width = build_statuscol_str(wp, lnum, relnum, buf, stcp);
   // Force a redraw in case of error or when truncated
-  if (*wp->w_p_stc == NUL || (stcp->truncate > 0 && wp->w_nrwidth < MAX_NUMBERWIDTH)) {
+  if (*wp->w_p_stc == NUL || (width > stcp->width && stcp->width < MAX_STCWIDTH)) {
     if (*wp->w_p_stc == NUL) {  // 'statuscolumn' reset due to error
       wp->w_nrwidth_line_count = 0;
       wp->w_nrwidth = (wp->w_p_nu || wp->w_p_rnu) * number_width(wp);
     } else {  // Avoid truncating 'statuscolumn'
+      wp->w_nrwidth += MIN(width - stcp->width, MAX_STCWIDTH - stcp->width);
       wp->w_nrwidth_width = wp->w_nrwidth;
-      wp->w_nrwidth = MIN(MAX_NUMBERWIDTH, wp->w_nrwidth + stcp->truncate);
     }
     wp->w_redr_statuscol = true;
     return;
diff --git a/src/nvim/option_vars.h b/src/nvim/option_vars.h
index dbbbfc6632..43664807cb 100644
--- a/src/nvim/option_vars.h
+++ b/src/nvim/option_vars.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "nvim/macros_defs.h"
+#include "nvim/sign_defs.h"
 #include "nvim/types_defs.h"
 
 // option_vars.h: definition of global variables for settable options
@@ -785,7 +786,10 @@ EXTERN int p_cdh;               ///< 'cdhome'
 
 #define SB_MAX 100000  // Maximum 'scrollback' value.
 
-#define MAX_NUMBERWIDTH 20      // used for 'numberwidth' and 'statuscolumn'
+#define MAX_NUMBERWIDTH 20      // used for 'numberwidth'
+
+// Maximum 'statuscolumn' width: number + sign + fold columns
+#define MAX_STCWIDTH MAX_NUMBERWIDTH + SIGN_SHOW_MAX * SIGN_WIDTH + 9
 
 #define TABSTOP_MAX 9999
 
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index a997a41b77..74808485ba 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -8021,9 +8021,13 @@ return {
         %s	sign column for currently drawn line
         %C	fold column for currently drawn line
 
-        NOTE: To draw the sign and fold columns, their items must be included in
-        'statuscolumn'. Even when they are not included, the status column width
-        will adapt to the 'signcolumn' and 'foldcolumn' width.
+        The 'statuscolumn' width follows that of the default columns and
+        adapts to the |'numberwidth'|, |'signcolumn'| and |'foldcolumn'| option
+        values (regardless of whether the sign and fold items are present).
+        Aditionally, the 'statuscolumn' grows with the size of the evaluated
+        format string, up to a point (following the maximum size of the default
+        fold, sign and number columns). Shrinking only happens when the number
+        of lines in a buffer changes, or the 'statuscolumn' option is set.
 
         The |v:lnum|    variable holds the line number to be drawn.
         The |v:relnum|  variable holds the relative line number to be drawn.
diff --git a/src/nvim/statusline.c b/src/nvim/statusline.c
index 3575b6fba3..1f00b406ec 100644
--- a/src/nvim/statusline.c
+++ b/src/nvim/statusline.c
@@ -1964,11 +1964,7 @@ int build_stl_str_hl(win_T *wp, char *out, size_t outlen, char *fmt, OptIndex op
   // What follows is post-processing to handle alignment and highlighting.
 
   int width = vim_strsize(out);
-  // Return truncated width for 'statuscolumn'
-  if (stcp != NULL && width > stcp->width) {
-    stcp->truncate = width - stcp->width;
-  }
-  if (maxwidth > 0 && width > maxwidth) {
+  if (maxwidth > 0 && width > maxwidth && (!stcp || width > MAX_STCWIDTH)) {
     // Result is too long, must truncate somewhere.
     int item_idx = 0;
     char *trunc_p;
diff --git a/src/nvim/statusline_defs.h b/src/nvim/statusline_defs.h
index a8588b54d7..118f4a257b 100644
--- a/src/nvim/statusline_defs.h
+++ b/src/nvim/statusline_defs.h
@@ -58,7 +58,6 @@ typedef struct {
   int width;                           ///< width of the status column
   int num_attr;                        ///< default highlight attr
   int sign_cul_id;                     ///< cursorline sign highlight id
-  int truncate;                        ///< truncated width
   bool draw;                           ///< whether to draw the statuscolumn
   bool use_cul;                        ///< whether to use cursorline attrs
   stl_hlrec_t *hlrec;                  ///< highlight groups