parseopt: add PARSE_OPT_NO_INTERNAL_HELP

Add a parseopt flag, PARSE_OPT_NO_INTERNAL_HELP, that turns off internal
handling of -h, --help and --help-all.  This allows the implementation
of custom help option handlers or incremental parsers.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.c

@@ -253,6 +253,8 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 		       const struct option *options,
 		       const char * const usagestr[])
 {
+	int internal_help = !(ctx->flags & PARSE_OPT_NO_INTERNAL_HELP);
+
 	/* we must reset ->opt, unknown short option leave it dangling */
 	ctx->opt = NULL;
 
@@ -268,7 +270,7 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 
 		if (arg[1] != '-') {
 			ctx->opt = arg + 1;
-			if (*ctx->opt == 'h')
+			if (internal_help && *ctx->opt == 'h')
 				return parse_options_usage(usagestr, options);
 			switch (parse_short_opt(ctx, options)) {
 			case -1:
@@ -279,7 +281,7 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 			if (ctx->opt)
 				check_typos(arg + 1, options);
 			while (ctx->opt) {
-				if (*ctx->opt == 'h')
+				if (internal_help && *ctx->opt == 'h')
 					return parse_options_usage(usagestr, options);
 				switch (parse_short_opt(ctx, options)) {
 				case -1:
@@ -306,9 +308,9 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 			break;
 		}
 
-		if (!strcmp(arg + 2, "help-all"))
+		if (internal_help && !strcmp(arg + 2, "help-all"))
 			return usage_with_options_internal(usagestr, options, 1);
-		if (!strcmp(arg + 2, "help"))
+		if (internal_help && !strcmp(arg + 2, "help"))
 			return parse_options_usage(usagestr, options);
 		switch (parse_long_opt(ctx, arg + 2, options)) {
 		case -1:

parse-options.h

@@ -22,6 +22,7 @@ enum parse_opt_flags {
 	PARSE_OPT_STOP_AT_NON_OPTION = 2,
 	PARSE_OPT_KEEP_ARGV0 = 4,
 	PARSE_OPT_KEEP_UNKNOWN = 8,
+	PARSE_OPT_NO_INTERNAL_HELP = 16,
 };
 
 enum parse_opt_option_flags {