Add :show command to display special symbols for whitespaces

Enable/disable by setting to 0/1 respectively:

 :set show spaces=0 tabs=0 newlines=1

config.def.h

@@ -827,6 +827,11 @@ enum {
 	COLOR_COMMENT      = COLOR_SYNTAX7,
 	COLOR_IDENTIFIER   = COLOR_SYNTAX8,
 	COLOR_TYPE         = COLOR_SYNTAX9,
+	COLOR_WHITESPACE   = COLOR_COMMENT,
+	COLOR_SPACES       = COLOR_WHITESPACE,
+	COLOR_TABS         = COLOR_WHITESPACE,
+	COLOR_EOL          = COLOR_WHITESPACE,
+	COLOR_EOF          = COLOR_WHITESPACE,
 };
 
 static Color colors[] = {
@@ -894,6 +899,12 @@ static Color colors[] = {
 	&colors[COLOR_PREPROCESSOR], \
 }
 
+#define SYNTAX_SPACES    { "\xC2\xB7",     &colors[COLOR_SPACES] }
+#define SYNTAX_TABS      { "\xE2\x96\xB6", &colors[COLOR_TABS]   }
+#define SYNTAX_TABS_FILL { " ",            &colors[COLOR_TABS]   }
+#define SYNTAX_EOL       { "\xE2\x8F\x8E", &colors[COLOR_EOL]    }
+#define SYNTAX_EOF       { "~",            &colors[COLOR_EOF]    }
+
 /* these rules are applied top to bottom, first match wins. Therefore more 'greedy'
  * rules such as for comments should be the first entries.
  *
@@ -905,8 +916,16 @@ static Syntax syntaxes[] = {{
 	.settings = (const char*[]){
 		"set number",
 		"set autoindent",
+		"set show spaces=0 tabs=1 newlines=1",
 		NULL
 	},
+	.symbols = {
+		SYNTAX_SPACES,
+		SYNTAX_TABS,
+		SYNTAX_TABS_FILL,
+		SYNTAX_EOL,
+		SYNTAX_EOF,
+	},
 	.rules = {
 		SYNTAX_MULTILINE_COMMENT,
 		SYNTAX_SINGLE_LINE_COMMENT,

syntax.h

@@ -15,12 +15,27 @@ typedef struct {
 	regex_t regex;  /* compiled form of the above rule */
 } SyntaxRule;
 
+typedef struct {
+	char *symbol;
+	Color *color;
+} SyntaxSymbol;
+
+enum {
+	SYNTAX_SYMBOL_SPACE,
+	SYNTAX_SYMBOL_TAB,
+	SYNTAX_SYMBOL_TAB_FILL,
+	SYNTAX_SYMBOL_EOL,
+	SYNTAX_SYMBOL_EOF,
+	SYNTAX_SYMBOL_LAST,
+};
+
 typedef struct Syntax Syntax;
 struct Syntax {               /* a syntax definition */
 	char *name;           /* syntax name */
 	char *file;           /* apply to files matching this regex */
 	regex_t file_regex;   /* compiled file name regex */
 	const char **settings;/* settings associated with this file type */
+	SyntaxSymbol symbols[SYNTAX_SYMBOL_LAST]; /* symbols for white space handling */
 	SyntaxRule rules[24]; /* all rules for this file type */
 };
 

ui-curses.c

@@ -213,7 +213,7 @@ static void ui_window_draw_sidebar(UiCursesWin *win, const Line *line) {
 		size_t cursor_lineno = view_cursor_getpos(win->view).line;
 		werase(win->winside);
 		for (const Line *l = line; l; l = l->next, i++) {
-			if (l->lineno != prev_lineno) {
+			if (l->lineno && l->lineno != prev_lineno) {
 				if (win->options & UI_OPTION_LINE_NUMBERS_ABSOLUTE) {
 					mvwprintw(win->winside, i, 0, "%*u", sidebar_width-1, l->lineno);
 				} else if (win->options & UI_OPTION_LINE_NUMBERS_RELATIVE) {
@@ -376,6 +376,8 @@ static void ui_window_draw_text(UiWin *w, const Line *line) {
 				wattrset(win->win, l->cells[x].attr);
 				waddstr(win->win, l->cells[x].data);
 			}
+			if (l->width != win->width - win->sidebar_width)
+				waddstr(win->win, "\n");
 		}
 		wclrtoeol(win->win);
 	}

view.c

@@ -51,9 +51,26 @@ struct View {               /* viewable area, showing part of a file */
 	Line *line;         /* used while drawing view content, line where next char will be drawn */
 	int col;            /* used while drawing view content, column where next char will be drawn */
 	Syntax *syntax;     /* syntax highlighting definitions for this view or NULL */
+	SyntaxSymbol *symbols[SYNTAX_SYMBOL_LAST]; /* symbols to use for white spaces etc */
 	int tabwidth;       /* how many spaces should be used to display a tab character */
 };
 
+static SyntaxSymbol symbols_none[] = {
+	{ " " }, /* spaces */
+	{ " " }, /* tab first cell */
+	{ " " }, /* tab remaining cells */
+	{ "" },  /* eol */
+	{ "~" }, /* eof */
+};
+
+static SyntaxSymbol symbols_default[] = {
+	{ "\xC2\xB7" },     /* spaces */
+	{ "\xE2\x96\xB6" }, /* tab first cell */
+	{ " " },            /* tab remaining cells */
+	{ "\xE2\x8F\x8E" }, /* eol */
+	{ "~" },            /* eof */
+};
+
 static void view_clear(View *view);
 static bool view_addch(View *view, Cell *cell);
 static size_t view_cursor_update(View *view);
@@ -134,6 +151,8 @@ static bool view_addch(View *view, Cell *cell) {
 
 	switch (cell->data[0]) {
 	case '\t':
+		cell->istab = true;
+		cell->width = 1;
 		width = view->tabwidth - (view->col % view->tabwidth);
 		for (int w = 0; w < width; w++) {
 			if (view->col + 1 > view->width) {
@@ -143,23 +162,18 @@ static bool view_addch(View *view, Cell *cell) {
 					return false;
 				view->line->lineno = lineno;
 			}
-			if (w == 0) {
-				/* first cell of a tab has a length of 1 */
-				view->line->cells[view->col].len = cell->len;
-				view->line->len += cell->len;
-			} else {
-				/* all remaining ones have a lenght of zero */
-				view->line->cells[view->col].len = 0;
-			}
-			/* but all are marked as part of a tabstop */
-			view->line->cells[view->col].width = 1;
-			view->line->cells[view->col].data[0] = ' ';
-			view->line->cells[view->col].data[1] = '\0';
-			view->line->cells[view->col].istab = true;
-			view->line->cells[view->col].attr = cell->attr;
-			view->line->width++;
+
+			cell->len = w == 0 ? 1 : 0;
+			int t = w == 0 ? SYNTAX_SYMBOL_TAB : SYNTAX_SYMBOL_TAB_FILL;
+			strncpy(cell->data, view->symbols[t]->symbol, sizeof(cell->data));
+			if (view->symbols[t]->color)
+				cell->attr = view->symbols[t]->color->attr;
+			view->line->cells[view->col] = *cell;
+			view->line->len += cell->len;
+			view->line->width += cell->width;
 			view->col++;
 		}
+		cell->len = 1;
 		return true;
 	case '\n':
 		cell->width = 1;
@@ -170,6 +184,11 @@ static bool view_addch(View *view, Cell *cell) {
 				return false;
 			view->line->lineno = lineno;
 		}
+
+		strncpy(cell->data, view->symbols[SYNTAX_SYMBOL_EOL]->symbol, sizeof(cell->data));
+		if (view->symbols[SYNTAX_SYMBOL_EOL]->color)
+			cell->attr = view->symbols[SYNTAX_SYMBOL_EOL]->color->attr;
+
 		view->line->cells[view->col] = *cell;
 		view->line->len += cell->len;
 		view->line->width += cell->width;
@@ -193,6 +212,12 @@ static bool view_addch(View *view, Cell *cell) {
 			};
 		}
 
+		if (cell->data[0] == ' ') {
+			strncpy(cell->data, view->symbols[SYNTAX_SYMBOL_SPACE]->symbol, sizeof(cell->data));
+			if (view->symbols[SYNTAX_SYMBOL_SPACE]->color)
+				cell->attr = view->symbols[SYNTAX_SYMBOL_SPACE]->color->attr;
+		}
+
 		if (view->col + cell->width > view->width) {
 			for (int i = view->col; i < view->width; i++)
 				view->line->cells[i] = empty;
@@ -452,7 +477,15 @@ void view_draw(View *view) {
 	/* set end of vieviewg region */
 	view->end = pos;
 	view->lastline = view->line ? view->line : view->bottomline;
-	view->lastline->next = NULL;
+
+	for (Line *l = view->lastline->next; l; l = l->next) {
+		strncpy(l->cells[0].data, view->symbols[SYNTAX_SYMBOL_EOF]->symbol, sizeof(l->cells[0].data));
+		if (view->symbols[SYNTAX_SYMBOL_EOF]->color)
+			l->cells[0].attr =view->symbols[SYNTAX_SYMBOL_EOF]->color->attr;
+		l->width = 1;
+		l->len = 0;
+	}
+
 	view_cursor_sync(view);
 	if (view->ui)
 		view->ui->draw_text(view->ui, view->topline);
@@ -505,6 +538,7 @@ View *view_new(Text *text, ViewEvent *events) {
 	view->text = text;
 	view->events = events;
 	view->tabwidth = 8;
+	view_symbols_set(view, 0);
 
 	if (!view_resize(view, 1, 1)) {
 		view_free(view);
@@ -776,12 +810,40 @@ void view_selection_start(View *view) {
 
 void view_syntax_set(View *view, Syntax *syntax) {
 	view->syntax = syntax;
+	for (int i = 0; i < LENGTH(view->symbols); i++) {
+		if (syntax && syntax->symbols[i].symbol)
+			view->symbols[i] = &syntax->symbols[i];
+		else
+			view->symbols[i] = &symbols_none[i];
+	}
 }
 
 Syntax *view_syntax_get(View *view) {
 	return view->syntax;
 }
 
+void view_symbols_set(View *view, int flags) {
+	for (int i = 0; i < LENGTH(view->symbols); i++) {
+		if (flags & (1 << i)) {
+			if (view->syntax && view->syntax->symbols[i].symbol)
+				view->symbols[i] = &view->syntax->symbols[i];
+			else
+				view->symbols[i] = &symbols_default[i];
+		} else {
+			view->symbols[i] = &symbols_none[i];
+		}
+	}
+}
+
+int view_symbols_get(View *view) {
+	int flags = 0;
+	for (int i = 0; i < LENGTH(view->symbols); i++) {
+		if (view->symbols[i] != &symbols_none[i])
+			flags |= (1 << i);
+	}
+	return flags;
+}
+
 size_t view_screenline_goto(View *view, int n) {
 	size_t pos = view->start;
 	for (Line *line = view->topline; --n > 0 && line != view->lastline; line = line->next)

view.h

@@ -115,5 +115,7 @@ bool view_viewport_down(View *view, int n);
 /* associate a set of syntax highlighting rules to this window. */
 void view_syntax_set(View*, Syntax*);
 Syntax *view_syntax_get(View*);
+void view_symbols_set(View*, int flags);
+int view_symbols_get(View*);
 
 #endif

vis.c

@@ -1339,6 +1339,7 @@ static bool cmd_set(Filerange *range, enum CmdOpt cmdopt, const char *argv[]) {
 		OPTION_EXPANDTAB,
 		OPTION_TABWIDTH,
 		OPTION_SYNTAX,
+		OPTION_SHOW,
 		OPTION_NUMBER,
 		OPTION_NUMBER_RELATIVE,
 	};
@@ -1349,6 +1350,7 @@ static bool cmd_set(Filerange *range, enum CmdOpt cmdopt, const char *argv[]) {
 		[OPTION_EXPANDTAB]       = { { "expandtab", "et"        }, OPTION_TYPE_BOOL   },
 		[OPTION_TABWIDTH]        = { { "tabwidth", "tw"         }, OPTION_TYPE_NUMBER },
 		[OPTION_SYNTAX]          = { { "syntax"                 }, OPTION_TYPE_STRING, true },
+		[OPTION_SHOW]            = { { "show"                   }, OPTION_TYPE_STRING },
 		[OPTION_NUMBER]          = { { "numbers", "nu"          }, OPTION_TYPE_BOOL   },
 		[OPTION_NUMBER_RELATIVE] = { { "relativenumbers", "rnu" }, OPTION_TYPE_BOOL   },
 	};
@@ -1448,6 +1450,36 @@ static bool cmd_set(Filerange *range, enum CmdOpt cmdopt, const char *argv[]) {
 		else
 			editor_info_show(vis, "Unknown syntax definition: `%s'", argv[2]);
 		break;
+	case OPTION_SHOW:
+		if (!argv[2]) {
+			editor_info_show(vis, "Expecting: spaces, tabs, newlines");
+			return false;
+		}
+		char *keys[] = { "spaces", "tabs", "newlines" };
+		int values[] = {
+			1 << SYNTAX_SYMBOL_SPACE,
+			(1 << SYNTAX_SYMBOL_TAB)|(1 << SYNTAX_SYMBOL_TAB_FILL),
+			1 << SYNTAX_SYMBOL_EOL
+		};
+		int flags = view_symbols_get(vis->win->view);
+		for (const char **args = &argv[2]; *args; args++) {
+			for (int i = 0; i < LENGTH(keys); i++) {
+				if (strcmp(*args, keys[i]) == 0) {
+					flags |= values[i];
+				} else if (strstr(*args, keys[i]) == *args) {
+					bool show;
+					const char *v = *args + strlen(keys[i]);
+					if (*v == '=' && parse_bool(v+1, &show)) {
+						if (show)
+							flags |= values[i];
+						else
+							flags &= ~values[i];
+					}
+				}
+			}
+		}
+		view_symbols_set(vis->win->view, flags);
+		break;
 	case OPTION_NUMBER:
 		editor_window_options(vis->win, arg.b ? UI_OPTION_LINE_NUMBERS_ABSOLUTE :
 			UI_OPTION_LINE_NUMBERS_NONE);