patch 8.2.3424: a sequence of spaces is hard to see in list mode

Problem:    A sequence of spaces is hard to see in list mode.
Solution:   Add the "multispace" option to 'listchars'. (closes #8834)

runtime/doc/options.txt

@@ -4939,16 +4939,25 @@ A jump table for the options with a short description can be found at |Q_op|.
 							*lcs-space*
 	  space:c	Character to show for a space.  When omitted, spaces
 			are left blank.
+							*lcs-multispace*
+	  multispace:c...
+	 		One or more characters to use cyclically to show for
+	 		multiple consecutive spaces.  Overrides the "space"
+			setting, except for single spaces.  When omitted, the
+			"space" setting is used.  For example,
+			`:set listchars=multispace:---+` shows ten consecutive
+			spaces as:
+				---+---+--
 							*lcs-lead*
 	  lead:c	Character to show for leading spaces.  When omitted,
-			leading spaces are blank.  Overrides the "space"
+			leading spaces are blank.  Overrides the "space" and
-			setting for leading spaces.  You can combine it with
+			"multispace" settings for leading spaces.  You can
-			"tab:", for example: >
+			combine it with "tab:", for example: >
 				:set listchars+=tab:>-,lead:.
 <							*lcs-trail*
 	  trail:c	Character to show for trailing spaces.  When omitted,
-			trailing spaces are blank.  Overrides the "space"
+			trailing spaces are blank.  Overrides the "space" and
-			setting for trailing spaces.
+			"multispace" settings for trailing spaces.
 							*lcs-extends*
 	  extends:c	Character to show in the last column, when 'wrap' is
 			off and the line continues beyond the right of the

src/drawline.c

@@ -340,6 +340,8 @@ win_line(
 #endif
     colnr_T	trailcol = MAXCOL;	// start of trailing spaces
     colnr_T	leadcol = 0;		// start of leading spaces
+    int		in_multispace = FALSE;	// in multiple consecutive spaces
+    int		multispace_pos = 0;	// position in lcs-multispace string
 #ifdef FEAT_LINEBREAK
     int		need_showbreak = FALSE; // overlong line, skipping first x
 					// chars
@@ -736,6 +738,7 @@ win_line(
     if (wp->w_p_list)
     {
 	if (wp->w_lcs_chars.space
+		|| wp->w_lcs_chars.multispace != NULL
 		|| wp->w_lcs_chars.trail
 		|| wp->w_lcs_chars.lead
 		|| wp->w_lcs_chars.nbsp)
@@ -2011,6 +2014,11 @@ win_line(
 		}
 #endif
 
+		in_multispace = c == ' '
+		    && ((ptr > line + 1 && ptr[-2] == ' ') || *ptr == ' ');
+		if (!in_multispace)
+		    multispace_pos = 0;
+
 		// 'list': Change char 160 to 'nbsp' and space to 'space'
 		// setting in 'listchars'.  But not when the character is
 		// followed by a composing character (use mb_l to check that).
@@ -2022,12 +2030,21 @@ win_line(
 			     && wp->w_lcs_chars.nbsp)
 			    || (c == ' '
 				&& mb_l == 1
-				&& wp->w_lcs_chars.space
+				&& (wp->w_lcs_chars.space
+				    || (in_multispace
+					&& wp->w_lcs_chars.multispace != NULL))
 				&& ptr - line >= leadcol
 				&& ptr - line <= trailcol)))
 		{
-		    c = (c == ' ') ? wp->w_lcs_chars.space :
+		    if (in_multispace && wp->w_lcs_chars.multispace != NULL)
-							wp->w_lcs_chars.nbsp;
+		    {
+			c = wp->w_lcs_chars.multispace[multispace_pos++];
+			if (wp->w_lcs_chars.multispace[multispace_pos] == NUL)
+			    multispace_pos = 0;
+		    }
+		    else
+			c = (c == ' ') ? wp->w_lcs_chars.space
+					: wp->w_lcs_chars.nbsp;
 		    if (area_attr == 0 && search_attr == 0)
 		    {
 			n_attr = 1;

src/message.c

@@ -1841,6 +1841,8 @@ msg_prt_line(char_u *s, int list)
     int		attr = 0;
     char_u	*trail = NULL;
     char_u	*lead = NULL;
+    int		in_multispace = FALSE;
+    int		multispace_pos = 0;
     int		l;
     char_u	buf[MB_MAXBYTES + 1];
 
@@ -1912,6 +1914,10 @@ msg_prt_line(char_u *s, int list)
 	{
 	    attr = 0;
 	    c = *s++;
+	    in_multispace = c == ' '
+		&& ((col > 0 && s[-2] == ' ') || *s == ' ');
+	    if (!in_multispace)
+		multispace_pos = 0;
 	    if (c == TAB && (!list || curwin->w_lcs_chars.tab1))
 	    {
 		// tab amount depends on current column
@@ -1963,22 +1969,33 @@ msg_prt_line(char_u *s, int list)
 		// the same in plain text.
 		attr = HL_ATTR(HLF_8);
 	    }
-	    else if (c == ' ' && lead != NULL && s <= lead)
+	    else if (c == ' ')
+	    {
+		if (lead != NULL && s <= lead)
 		{
 		    c = curwin->w_lcs_chars.lead;
 		    attr = HL_ATTR(HLF_8);
 		}
-	    else if (c == ' ' && trail != NULL && s > trail)
+		else if (trail != NULL && s > trail)
 		{
 		    c = curwin->w_lcs_chars.trail;
 		    attr = HL_ATTR(HLF_8);
 		}
-	    else if (c == ' ' && list && curwin->w_lcs_chars.space != NUL)
+		else if (list && in_multispace
+			&& curwin->w_lcs_chars.multispace != NULL)
+		{
+		    c = curwin->w_lcs_chars.multispace[multispace_pos++];
+		    if (curwin->w_lcs_chars.multispace[multispace_pos] == NUL)
+			multispace_pos = 0;
+		    attr = HL_ATTR(HLF_8);
+		}
+		else if (list && curwin->w_lcs_chars.space != NUL)
 		{
 		    c = curwin->w_lcs_chars.space;
 		    attr = HL_ATTR(HLF_8);
 		}
 	    }
+	}
 
 	if (c == NUL)
 	    break;

src/screen.c

@@ -4787,6 +4787,8 @@ set_chars_option(win_T *wp, char_u **varp)
     int		round, i, len, entries;
     char_u	*p, *s;
     int		c1 = 0, c2 = 0, c3 = 0;
+    char_u	*last_multispace;	// Last occurrence of "multispace:"
+    int		multispace_len = 0;	// Length of lcs-multispace string
     struct charstab
     {
 	int	*cp;
@@ -4853,6 +4855,13 @@ set_chars_option(win_T *wp, char_u **varp)
 	    {
 		lcs_chars.tab1 = NUL;
 		lcs_chars.tab3 = NUL;
+		if (multispace_len)
+		{
+		    lcs_chars.multispace = ALLOC_MULT(int, multispace_len + 1);
+		    lcs_chars.multispace[multispace_len] = NUL;
+		}
+		else
+		    lcs_chars.multispace = NULL;
 	    }
 	    else
 	    {
@@ -4877,19 +4886,19 @@ set_chars_option(win_T *wp, char_u **varp)
 		    s = p + len + 1;
 		    c1 = mb_ptr2char_adv(&s);
 		    if (mb_char2cells(c1) > 1)
-			continue;
+			return e_invarg;
 		    if (tab[i].cp == &lcs_chars.tab2)
 		    {
 			if (*s == NUL)
-			    continue;
+			    return e_invarg;
 			c2 = mb_ptr2char_adv(&s);
 			if (mb_char2cells(c2) > 1)
-			    continue;
+			    return e_invarg;
 			if (!(*s == ',' || *s == NUL))
 			{
 			    c3 = mb_ptr2char_adv(&s);
 			    if (mb_char2cells(c3) > 1)
-				continue;
+				return e_invarg;
 			}
 		    }
 
@@ -4914,13 +4923,57 @@ set_chars_option(win_T *wp, char_u **varp)
 	    }
 
 	    if (i == entries)
+	    {
+		len = STRLEN("multispace");
+		if ((varp == &p_lcs || varp == &wp->w_p_lcs)
+			&& STRNCMP(p, "multispace", len) == 0
+			&& p[len] == ':'
+			&& p[len + 1] != NUL)
+		{
+		    s = p + len + 1;
+		    if (round == 0)
+		    {
+			// Get length of lcs-multispace string in first round
+			last_multispace = p;
+			multispace_len = 0;
+			while (*s != NUL && *s != ',')
+			{
+			    c1 = mb_ptr2char_adv(&s);
+			    if (mb_char2cells(c1) > 1)
 				return e_invarg;
+			    ++multispace_len;
+			}
+			if (multispace_len == 0)
+			    // lcs-multispace cannot be an empty string
+			    return e_invarg;
+			p = s;
+		    }
+		    else
+		    {
+			int multispace_pos = 0;
+			while (*s != NUL && *s != ',')
+			{
+			    c1 = mb_ptr2char_adv(&s);
+			    if (p == last_multispace)
+				lcs_chars.multispace[multispace_pos++] = c1;
+			}
+			p = s;
+		    }
+		}
+		else
+		    return e_invarg;
+	    }
+
 	    if (*p == ',')
 		++p;
 	}
     }
     if (tab == lcstab)
+    {
+	if (wp->w_lcs_chars.multispace != NULL)
+	    vim_free(wp->w_lcs_chars.multispace);
 	wp->w_lcs_chars = lcs_chars;
+    }
 
     return NULL;	// no error
 }

src/structs.h

@@ -3376,6 +3376,7 @@ typedef struct
     int		tab3;
     int		trail;
     int		lead;
+    int		*multispace;
 #ifdef FEAT_CONCEAL
     int		conceal;
 #endif

src/testdir/test_listchars.vim

@@ -142,6 +142,93 @@ func Test_listchars()
 
   call assert_equal(expected, split(execute("%list"), "\n"))
 
+  " Test multispace
+  normal ggdG
+  set listchars&
+  set listchars+=multispace:yYzZ
+  set list
+
+  call append(0, [
+	      \ '    ffff    ',
+	      \ '  i i     gg',
+	      \ ' h          ',
+	      \ '          j ',
+	      \ '    0  0    ',
+	      \ ])
+
+  let expected = [
+	      \ 'yYzZffffyYzZ$',
+	      \ 'yYi iyYzZygg$',
+	      \ ' hyYzZyYzZyY$',
+	      \ 'yYzZyYzZyYj $',
+	      \ 'yYzZ0yY0yYzZ$',
+              \ '$'
+	      \ ]
+  redraw!
+  for i in range(1, 5)
+    call cursor(i, 1)
+    call assert_equal([expected[i - 1]], ScreenLines(i, virtcol('$')))
+  endfor
+
+  call assert_equal(expected, split(execute("%list"), "\n"))
+
+  " the last occurrence of 'multispace:' is used
+  set listchars+=space:x,multispace:XyY
+
+  let expected = [
+	      \ 'XyYXffffXyYX$',
+	      \ 'XyixiXyYXygg$',
+	      \ 'xhXyYXyYXyYX$',
+	      \ 'XyYXyYXyYXjx$',
+	      \ 'XyYX0Xy0XyYX$',
+              \ '$'
+	      \ ]
+  redraw!
+  for i in range(1, 5)
+    call cursor(i, 1)
+    call assert_equal([expected[i - 1]], ScreenLines(i, virtcol('$')))
+  endfor
+
+  call assert_equal(expected, split(execute("%list"), "\n"))
+
+  set listchars+=lead:>,trail:<
+
+  let expected = [
+	      \ '>>>>ffff<<<<$',
+	      \ '>>ixiXyYXygg$',
+	      \ '>h<<<<<<<<<<$',
+	      \ '>>>>>>>>>>j<$',
+	      \ '>>>>0Xy0<<<<$',
+              \ '$'
+	      \ ]
+  redraw!
+  for i in range(1, 5)
+    call cursor(i, 1)
+    call assert_equal([expected[i - 1]], ScreenLines(i, virtcol('$')))
+  endfor
+
+  call assert_equal(expected, split(execute("%list"), "\n"))
+
+  " removing 'multispace:'
+  set listchars-=multispace:XyY
+  set listchars-=multispace:yYzZ
+
+  let expected = [
+	      \ '>>>>ffff<<<<$',
+	      \ '>>ixixxxxxgg$',
+	      \ '>h<<<<<<<<<<$',
+	      \ '>>>>>>>>>>j<$',
+	      \ '>>>>0xx0<<<<$',
+              \ '$'
+	      \ ]
+  redraw!
+  for i in range(1, 5)
+    call cursor(i, 1)
+    call assert_equal([expected[i - 1]], ScreenLines(i, virtcol('$')))
+  endfor
+
+  call assert_equal(expected, split(execute("%list"), "\n"))
+
   " test nbsp
   normal ggdG
   set listchars=nbsp:X,trail:Y
@@ -191,20 +278,69 @@ func Test_listchars_unicode()
   set encoding=utf-8
   set ff=unix
 
-  set listchars=eol:⇔,space:␣,nbsp:≠,tab:←↔→
+  set listchars=eol:⇔,space:␣,multispace:≡≢≣,nbsp:≠,tab:←↔→
   set list
 
   let nbsp = nr2char(0xa0)
-  call append(0, ["a\tb c" .. nbsp .. "d"])
+  call append(0, ["        a\tb c" .. nbsp .. "d  "])
-  let expected = ['a←↔↔↔↔↔→b␣c≠d⇔']
+  let expected = ['≡≢≣≡≢≣≡≢a←↔↔↔↔↔→b␣c≠d≡≢⇔']
   redraw!
   call cursor(1, 1)
   call assert_equal(expected, ScreenLines(1, virtcol('$')))
+
+  set listchars+=lead:⇨,trail:⇦
+  let expected = ['⇨⇨⇨⇨⇨⇨⇨⇨a←↔↔↔↔↔→b␣c≠d⇦⇦⇔']
+  redraw!
+  call cursor(1, 1)
+  call assert_equal(expected, ScreenLines(1, virtcol('$')))
+
   let &encoding=oldencoding
   enew!
   set listchars& ff&
 endfunction
 
+func Test_listchars_invalid()
+  enew!
+  set ff=unix
+
+  set listchars&
+  set list
+  set ambiwidth=double
+
+  " No colon
+  call assert_fails('set listchars=x', 'E474:')
+  call assert_fails('set listchars=x', 'E474:')
+  call assert_fails('set listchars=multispace', 'E474:')
+
+  " Too short
+  call assert_fails('set listchars=space:', 'E474:')
+  call assert_fails('set listchars=tab:x', 'E474:')
+  call assert_fails('set listchars=multispace:', 'E474:')
+
+  " One occurrence too short
+  call assert_fails('set listchars=space:,space:x', 'E474:')
+  call assert_fails('set listchars=space:x,space:', 'E474:')
+  call assert_fails('set listchars=tab:x,tab:xx', 'E474:')
+  call assert_fails('set listchars=tab:xx,tab:x', 'E474:')
+  call assert_fails('set listchars=multispace:,multispace:x', 'E474:')
+  call assert_fails('set listchars=multispace:x,multispace:', 'E474:')
+
+  " Too long
+  call assert_fails('set listchars=space:xx', 'E474:')
+  call assert_fails('set listchars=tab:xxxx', 'E474:')
+
+  " Has non-single width character
+  call assert_fails('set listchars=space:·', 'E474:')
+  call assert_fails('set listchars=tab:·x', 'E474:')
+  call assert_fails('set listchars=tab:x·', 'E474:')
+  call assert_fails('set listchars=tab:xx·', 'E474:')
+  call assert_fails('set listchars=multispace:·', 'E474:')
+  call assert_fails('set listchars=multispace:xxx·', 'E474:')
+
+  enew!
+  set ambiwidth& listchars& ff&
+endfunction
+
 " Tests that space characters following composing character won't get replaced
 " by listchars.
 func Test_listchars_composing()

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3424,
 /**/
     3423,
 /**/