short help: allow multi-line opthelp

When "-h" triggers the short-help in a command that implements its
option parsing using the parse-options API, the option help text is
shown with a single fprintf() as a long line.  When the text is
multi-line, the second and subsequent lines are not left padded,
that breaks the alignment across options.

Borrowing the idea from the advice API where its hint strings are
shown with (localized) "hint:" prefix, let's internally split the
(localized) help text into lines, and showing the first line, pad
the remaining lines to align.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.c

@@ -1109,6 +1109,7 @@ static enum parse_opt_result usage_with_options_internal(struct parse_opt_ctx_t
 	for (; opts->type != OPTION_END; opts++) {
 		size_t pos;
 		int pad;
+		const char *cp, *np;
 
 		if (opts->type == OPTION_SUBCOMMAND)
 			continue;
@@ -1157,7 +1158,16 @@ static enum parse_opt_result usage_with_options_internal(struct parse_opt_ctx_t
 				   (const char *)opts->value);
 			continue;
 		}
-		fprintf(outfile, "%*s%s\n", pad + USAGE_GAP, "", _(opts->help));
+
+		for (cp = _(opts->help); *cp; cp = np) {
+			np = strchrnul(cp, '\n');
+			fprintf(outfile,
+				"%*s%.*s\n", pad + USAGE_GAP, "",
+				(int)(np - cp), cp);
+			if (*np)
+				np++;
+			pad = USAGE_OPTS_WIDTH;
+		}
 	}
 	fputc('\n', outfile);
 

t/helper/test-parse-options.c

@@ -133,6 +133,8 @@ int cmd__parse_options(int argc, const char **argv)
 		OPT_STRING(0, "st", &string, "st", "get another string (pervert ordering)"),
 		OPT_STRING('o', NULL, &string, "str", "get another string"),
 		OPT_NOOP_NOARG(0, "obsolete"),
+		OPT_SET_INT_F(0, "longhelp", &integer, "help text of this entry\n"
+			      "spans multiple lines", 0, PARSE_OPT_NONEG),
 		OPT_STRING_LIST(0, "list", &list, "str", "add str to list"),
 		OPT_GROUP("Magic arguments"),
 		OPT_NUMBER_CALLBACK(&integer, "set integer to NUM",

t/t0040-parse-options.sh

@@ -35,6 +35,8 @@ String options
     --string2 <str>       get another string
     --st <st>             get another string (pervert ordering)
     -o <str>              get another string
+    --longhelp            help text of this entry
+                          spans multiple lines
     --list <str>          add str to list
 
 Magic arguments