defaults: set fillchars "foldsep" to box line #11702

"│" U+2502 BOX DRAWINGS LIGHT VERTICAL

Fallback to old default | if 'ambiwidth' is set.

runtime/doc/options.txt

@@ -2373,7 +2373,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	  fold:c	'·' or '-'	filling 'foldtext'
 	  foldopen:c	'-'		mark the beginning of a fold
 	  foldclose:c	'+'		show a closed fold
-	  foldsep:c	'|'		open fold middle marker
+	  foldsep:c	'│' or '|'      open fold middle marker
 	  diff:c	'-'		deleted lines of the 'diff' option
 	  msgsep:c	' '		message separator 'display'
 	  eob:c		'~'		empty lines at the end of a buffer
@@ -2382,7 +2382,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	"stlnc" the space will be used when there is highlighting, '^' or '='
 	otherwise.
 
-	If 'ambiwidth' is "double" then "vert" and "fold" default to
+	If 'ambiwidth' is "double" then "vert", "foldsep" and "fold" default to
 	single-byte alternatives.
 
 	Example: >

runtime/doc/vim_diff.txt

@@ -38,7 +38,7 @@ the differences.
 - 'directory' defaults to ~/.local/share/nvim/swap// (|xdg|), auto-created
 - 'display' defaults to "lastline,msgsep"
 - 'encoding' is UTF-8 (cf. 'fileencoding' for file-content encoding)
-- 'fillchars' defaults (in effect) to "vert:│,fold:·"
+- 'fillchars' defaults (in effect) to "vert:│,fold:·,sep:│"
 - 'formatoptions' defaults to "tcqj"
 - 'fsync' is disabled
 - 'history' defaults to 10000 (the maximum)

src/nvim/option.c

@@ -3544,7 +3544,7 @@ static char_u *set_chars_option(win_T *wp, char_u **varp, bool set)
     { &wp->w_p_fcs_chars.fold,    "fold",     183  },  // ·
     { &wp->w_p_fcs_chars.foldopen,   "foldopen",  '-'  },
     { &wp->w_p_fcs_chars.foldclosed, "foldclose", '+'  },
-    { &wp->w_p_fcs_chars.foldsep,    "foldsep",   '|' },
+    { &wp->w_p_fcs_chars.foldsep,    "foldsep",   9474 },  // │
     { &wp->w_p_fcs_chars.diff,    "diff",     '-'  },
     { &wp->w_p_fcs_chars.msgsep,  "msgsep",   ' '  },
     { &wp->w_p_fcs_chars.eob,     "eob",      '~'  },
@@ -3576,9 +3576,11 @@ static char_u *set_chars_option(win_T *wp, char_u **varp, bool set)
       // XXX: If ambiwidth=double then "|" and "·" take 2 columns, which is
       // forbidden (TUI limitation?). Set old defaults.
       fcs_tab[2].def = '|';
+      fcs_tab[6].def = '|';
       fcs_tab[3].def = '-';
     } else {
       fcs_tab[2].def = 9474;  // │
+      fcs_tab[6].def = 9474;  // │
       fcs_tab[3].def = 183;   // ·
     }
   }