vim-patch:9.1.1819: Cannot configure the inner foldlevel indicator (#36010)

Problem:  Cannot configure the inner foldlevel indicator for the
          foldcolumn
Solution: Add "foldinner" suboption value to the 'fillchar' option
          (Maria José Solano).

closes: vim/vim#18365

1a691afd27

Co-authored-by: Maria José Solano <majosolano99@gmail.com>

runtime/doc/fold.txt

@@ -585,7 +585,8 @@ A closed fold is indicated with a '+'.
 These characters can be changed with the 'fillchars' option.
 
 Where the fold column is too narrow to display all nested folds, digits are
-shown to indicate the nesting level.
+shown to indicate the nesting level.  To override this behavior you can use
+the "foldinner" character of the 'fillchars' option.
 
 The mouse can also be used to open and close folds by clicking in the
 fold column:

runtime/doc/news.txt

@@ -285,6 +285,7 @@ OPTIONS
 • 'completeopt' flag "nearest" sorts completion results by distance to cursor.
 • 'diffanchors' specifies addresses to anchor a diff.
 • 'diffopt' `inline:` configures diff highlighting for changes within a line.
+• 'fillchars' has new flag "foldinner".
 • 'grepformat' is now a |global-local| option.
 • 'maxsearchcount' sets maximum value for |searchcount()| and defaults to 999.
 • 'pummaxwidth' sets maximum width for the completion popup menu.

runtime/doc/options.txt

@@ -2861,6 +2861,9 @@ A jump table for the options with a short description can be found at |Q_op|.
 	  foldopen	'-'		mark the beginning of a fold
 	  foldclose	'+'		show a closed fold
 	  foldsep	'│' or '|'	open fold middle marker
+	  foldinner	none		character to show instead of the
+					numeric foldlevel when it would be
+					repeated in a narrow 'foldcolumn'
 	  diff		'-'		deleted lines of the 'diff' option
 	  msgsep	' '		message separator 'display'
 	  eob		'~'		empty lines at the end of a buffer

runtime/lua/vim/_meta/options.lua

@@ -2579,6 +2579,9 @@ vim.bo.ft = vim.bo.filetype
 ---   foldopen	'-'		mark the beginning of a fold
 ---   foldclose	'+'		show a closed fold
 ---   foldsep	'│' or '|'	open fold middle marker
+---   foldinner	none		character to show instead of the
+--- 				numeric foldlevel when it would be
+--- 				repeated in a narrow 'foldcolumn'
 ---   diff		'-'		deleted lines of the 'diff' option
 ---   msgsep	' '		message separator 'display'
 ---   eob		'~'		empty lines at the end of a buffer

src/nvim/buffer_defs.h

@@ -1077,6 +1077,7 @@ typedef struct {
   schar_T foldopen;    ///< when fold is open
   schar_T foldclosed;  ///< when fold is closed
   schar_T foldsep;     ///< continuous fold marker
+  schar_T foldinner;
   schar_T diff;
   schar_T msgsep;
   schar_T eob;

src/nvim/drawline.c

@@ -517,6 +517,8 @@ void fill_foldcolumn(win_T *wp, foldinfo_T foldinfo, linenr_T lnum, int attr, in
       symbol = wp->w_p_fcs_chars.foldopen;
     } else if (first_level == 1) {
       symbol = wp->w_p_fcs_chars.foldsep;
+    } else if (wp->w_p_fcs_chars.foldinner != NUL) {
+      symbol = wp->w_p_fcs_chars.foldinner;
     } else if (first_level + i <= 9) {
       symbol = schar_from_ascii('0' + first_level + i);
     } else {

src/nvim/options.lua

@@ -3262,6 +3262,9 @@ local options = {
           foldopen	'-'		mark the beginning of a fold
           foldclose	'+'		show a closed fold
           foldsep	'│' or '|'	open fold middle marker
+          foldinner	none		character to show instead of the
+        				numeric foldlevel when it would be
+        				repeated in a narrow 'foldcolumn'
           diff		'-'		deleted lines of the 'diff' option
           msgsep	' '		message separator 'display'
           eob		'~'		empty lines at the end of a buffer

src/nvim/optionstr.c

@@ -2260,6 +2260,7 @@ static const struct chars_tab fcs_tab[] = {
   CHARSTAB_ENTRY(&fcs_chars.foldopen,   "foldopen",  "-",  NULL),
   CHARSTAB_ENTRY(&fcs_chars.foldclosed, "foldclose", "+",  NULL),
   CHARSTAB_ENTRY(&fcs_chars.foldsep,    "foldsep",   "│",  "|"),
+  CHARSTAB_ENTRY(&fcs_chars.foldinner,  "foldinner", NULL, NULL),
   CHARSTAB_ENTRY(&fcs_chars.diff,       "diff",      "-",  NULL),
   CHARSTAB_ENTRY(&fcs_chars.msgsep,     "msgsep",    " ",  NULL),
   CHARSTAB_ENTRY(&fcs_chars.eob,        "eob",       "~",  NULL),

test/old/testdir/test_display.vim

@@ -343,6 +343,32 @@ func Test_fold_fillchars()
         \ ]
   call assert_equal(expected, lines)
 
+  " check setting foldinner
+  set fdc=1 foldmethod=indent foldlevel=10
+  call setline(1, ['one', '	two', '	two', '		three', '		three', 'four'])
+  let lines = ScreenLines([1, 6], 22)
+  let expected = [
+        \ ' one                  ',
+        \ '[        two          ',
+        \ '-        two          ',
+        \ '[                three',
+        \ '2                three',
+        \ ' four                 ',
+        \ ]
+  call assert_equal(expected, lines)
+
+  set fillchars+=foldinner:\ 
+  let lines = ScreenLines([1, 6], 22)
+  let expected = [
+        \ ' one                  ',
+        \ '[        two          ',
+        \ '-        two          ',
+        \ '[                three',
+        \ '                 three',
+        \ ' four                 ',
+        \ ]
+  call assert_equal(expected, lines)
+
   %bw!
   set fillchars& fdc& foldmethod& foldenable&
 endfunc