new feature: option --guidestripe that shows a vertical guiding bar

Option -J (--guidestripe) takes a column number as argument and then
shows a vertical, colored bar over the entire height of the buffer,
to aid the user in regulating the width of the text when the terminal
is wider than this desired width.

This fulfills https://bugs.debian.org/916392.
Requested-by: Arturo Borrero González <arturo@debian.org>
And fulfills https://savannah.gnu.org/bugs/?55315.
Requested-by: Bryan Christ <bryan.christ@gmail.com>

src/global.c

@@ -111,6 +111,8 @@ int editwincols = -1;
 		/* The number of usable columns in the edit window: COLS - margin. */
 int margin = 0;
 		/* The amount of space reserved at the left for line numbers. */
+ssize_t stripe_column = 0;
+		/* The column at which a vertical bar will be drawn. */
 
 filestruct *cutbuffer = NULL;
 		/* The buffer where we store cut text. */

src/nano.c

@@ -797,6 +797,10 @@ void usage(void)
 #endif
 #ifdef ENABLE_NANORC
 	print_opt("-I", "--ignorercfiles", N_("Don't look at nanorc files"));
+#endif
+#ifndef NANO_TINY
+	print_opt("-J <number>", "--guidestripe=<number>",
+					N_("Show a guiding bar at this column"));
 #endif
 	print_opt("-K", "--rawsequences",
 					N_("Fix numeric keypad key confusion problem"));
@@ -2022,6 +2026,7 @@ int main(int argc, char **argv)
 		{"tabstospaces", 0, NULL, 'E'},
 		{"locking", 0, NULL, 'G'},
 		{"historylog", 0, NULL, 'H'},
+		{"guidestripe", 1, NULL, 'J'},
 		{"noconvert", 0, NULL, 'N'},
 		{"positionlog", 0, NULL, 'P'},
 		{"smooth", 0, NULL, 'S'},
@@ -2092,7 +2097,7 @@ int main(int argc, char **argv)
 
 	while ((optchr =
 		getopt_long(argc, argv,
-				"ABC:DEFGHIKLMNOPQ:RST:UVWX:Y:Zabcdefghijklmno:pr:s:tuvwxyz$",
+				"ABC:DEFGHIJ:KLMNOPQ:RST:UVWX:Y:Zabcdefghijklmno:pr:s:tuvwxyz$",
 				long_options, NULL)) != -1) {
 		switch (optchr) {
 #ifndef NANO_TINY
@@ -2134,6 +2139,13 @@ int main(int argc, char **argv)
 				ignore_rcfiles = TRUE;
 				break;
 #endif
+			case 'J':
+				if (!parse_num(optarg, &stripe_column) || stripe_column <= 0) {
+					fprintf(stderr, _("Stripe column \"%s\" is invalid"), optarg);
+					fprintf(stderr, "\n");
+					exit(1);
+				}
+				break;
 			case 'K':
 				SET(RAW_SEQUENCES);
 				break;
@@ -2330,6 +2342,7 @@ int main(int argc, char **argv)
 		ssize_t fill_cmdline = fill;
 #endif
 #ifndef NANO_TINY
+		size_t stripeclm_cmdline = stripe_column;
 		char *backup_dir_cmdline = backup_dir;
 		char *word_chars_cmdline = word_chars;
 #endif
@@ -2376,6 +2389,8 @@ int main(int argc, char **argv)
 			fill = fill_cmdline;
 #endif
 #ifndef NANO_TINY
+		if (stripeclm_cmdline > 0)
+			stripe_column = stripeclm_cmdline;
 		if (backup_dir_cmdline != NULL) {
 			free(backup_dir);
 			backup_dir = backup_dir_cmdline;

src/proto.h

@@ -88,6 +88,7 @@ extern WINDOW *bottomwin;
 extern int editwinrows;
 extern int editwincols;
 extern int margin;
+extern ssize_t stripe_column;
 
 extern filestruct *cutbuffer;
 extern filestruct *cutbottom;

src/rcfile.c

@@ -102,6 +102,7 @@ static const rcoption rcopts[] = {
 	{"backupdir", 0},
 	{"casesensitive", CASE_SENSITIVE},
 	{"cutfromcursor", CUT_FROM_CURSOR},
+	{"guidestripe", 0},
 	{"locking", LOCKING},
 	{"matchbrackets", 0},
 	{"noconvert", NO_CONVERT},
@@ -1116,6 +1117,13 @@ void parse_rcfile(FILE *rcstream, bool syntax_only)
 		} else
 #endif
 #ifndef NANO_TINY
+		if (strcasecmp(rcopts[i].name, "guidestripe") == 0) {
+			if (!parse_num(option, &stripe_column) || stripe_column <= 0) {
+				rcfile_error(N_("Edge column \"%s\" is invalid"), option);
+				stripe_column = 0;
+			}
+			free(option);
+		}
 		if (strcasecmp(rcopts[i].name, "matchbrackets") == 0) {
 			matchbrackets = option;
 			if (has_blank_mbchars(matchbrackets)) {

src/winio.c

@@ -2685,6 +2685,15 @@ void edit_draw(filestruct *fileptr, const char *converted,
 	}
 #endif /* ENABLE_COLOR */
 
+	if (stripe_column > 0 && !inhelp) {
+		const char *text = converted + actual_x(converted, stripe_column - 1);
+		const char *striped_char = (*text == '\0') ? " " : text;
+
+		wattron(edit, interface_color_pair[ERROR_MESSAGE]);
+		mvwaddnstr(edit, row, margin + stripe_column - 1, striped_char, 1);
+		wattroff(edit, interface_color_pair[ERROR_MESSAGE]);
+	}
+
 #ifndef NANO_TINY
 	/* If the mark is on, and fileptr is at least partially selected, we
 	 * need to paint it. */