parse-options: add OPT_CMDMODE()

This can be used to define a set of mutually exclusive "command
mode" options, and automatically catch use of more than one from
that set as an error.

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

parse-options.c

@@ -43,8 +43,42 @@ static void fix_filename(const char *prefix, const char **file)
 	*file = xstrdup(prefix_filename(prefix, strlen(prefix), *file));
 }
 
+static int opt_command_mode_error(const struct option *opt,
+				  const struct option *all_opts,
+				  int flags)
+{
+	const struct option *that;
+	struct strbuf message = STRBUF_INIT;
+	struct strbuf that_name = STRBUF_INIT;
+
+	/*
+	 * Find the other option that was used to set the variable
+	 * already, and report that this is not compatible with it.
+	 */
+	for (that = all_opts; that->type != OPTION_END; that++) {
+		if (that == opt ||
+		    that->type != OPTION_CMDMODE ||
+		    that->value != opt->value ||
+		    that->defval != *(int *)opt->value)
+			continue;
+
+		if (that->long_name)
+			strbuf_addf(&that_name, "--%s", that->long_name);
+		else
+			strbuf_addf(&that_name, "-%c", that->short_name);
+		strbuf_addf(&message, ": incompatible with %s", that_name.buf);
+		strbuf_release(&that_name);
+		opterror(opt, message.buf, flags);
+		strbuf_release(&message);
+		return -1;
+	}
+	return opterror(opt, ": incompatible with something else", flags);
+}
+
 static int get_value(struct parse_opt_ctx_t *p,
-		     const struct option *opt, int flags)
+		     const struct option *opt,
+		     const struct option *all_opts,
+		     int flags)
 {
 	const char *s, *arg;
 	const int unset = flags & OPT_UNSET;
@@ -83,6 +117,16 @@ static int get_value(struct parse_opt_ctx_t *p,
 		*(int *)opt->value = unset ? 0 : opt->defval;
 		return 0;
 
+	case OPTION_CMDMODE:
+		/*
+		 * Giving the same mode option twice, although is unnecessary,
+		 * is not a grave error, so let it pass.
+		 */
+		if (*(int *)opt->value && *(int *)opt->value != opt->defval)
+			return opt_command_mode_error(opt, all_opts, flags);
+		*(int *)opt->value = opt->defval;
+		return 0;
+
 	case OPTION_SET_PTR:
 		*(void **)opt->value = unset ? NULL : (void *)opt->defval;
 		return 0;
@@ -143,12 +187,13 @@ static int get_value(struct parse_opt_ctx_t *p,
 
 static int parse_short_opt(struct parse_opt_ctx_t *p, const struct option *options)
 {
+	const struct option *all_opts = options;
 	const struct option *numopt = NULL;
 
 	for (; options->type != OPTION_END; options++) {
 		if (options->short_name == *p->opt) {
 			p->opt = p->opt[1] ? p->opt + 1 : NULL;
-			return get_value(p, options, OPT_SHORT);
+			return get_value(p, options, all_opts, OPT_SHORT);
 		}
 
 		/*
@@ -177,6 +222,7 @@ static int parse_short_opt(struct parse_opt_ctx_t *p, const struct option *optio
 static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
                           const struct option *options)
 {
+	const struct option *all_opts = options;
 	const char *arg_end = strchr(arg, '=');
 	const struct option *abbrev_option = NULL, *ambiguous_option = NULL;
 	int abbrev_flags = 0, ambiguous_flags = 0;
@@ -253,7 +299,7 @@ static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
 				continue;
 			p->opt = rest + 1;
 		}
-		return get_value(p, options, flags ^ opt_flags);
+		return get_value(p, options, all_opts, flags ^ opt_flags);
 	}
 
 	if (ambiguous_option)
@@ -265,18 +311,20 @@ static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
 			(abbrev_flags & OPT_UNSET) ?  "no-" : "",
 			abbrev_option->long_name);
 	if (abbrev_option)
-		return get_value(p, abbrev_option, abbrev_flags);
+		return get_value(p, abbrev_option, all_opts, abbrev_flags);
 	return -2;
 }
 
 static int parse_nodash_opt(struct parse_opt_ctx_t *p, const char *arg,
 			    const struct option *options)
 {
+	const struct option *all_opts = options;
+
 	for (; options->type != OPTION_END; options++) {
 		if (!(options->flags & PARSE_OPT_NODASH))
 			continue;
 		if (options->short_name == arg[0] && arg[1] == '\0')
-			return get_value(p, options, OPT_SHORT);
+			return get_value(p, options, all_opts, OPT_SHORT);
 	}
 	return -2;
 }

parse-options.h

@@ -13,6 +13,7 @@ enum parse_opt_type {
 	OPTION_COUNTUP,
 	OPTION_SET_INT,
 	OPTION_SET_PTR,
+	OPTION_CMDMODE,
 	/* options with arguments (usually) */
 	OPTION_STRING,
 	OPTION_INTEGER,
@@ -130,6 +131,8 @@ struct option {
 #define OPT_BOOL(s, l, v, h)        OPT_SET_INT(s, l, v, h, 1)
 #define OPT_SET_PTR(s, l, v, h, p)  { OPTION_SET_PTR, (s), (l), (v), NULL, \
 				      (h), PARSE_OPT_NOARG, NULL, (p) }
+#define OPT_CMDMODE(s, l, v, h, i) { OPTION_CMDMODE, (s), (l), (v), NULL, \
+				      (h), PARSE_OPT_NOARG|PARSE_OPT_NONEG, NULL, (i) }
 #define OPT_INTEGER(s, l, v, h)     { OPTION_INTEGER, (s), (l), (v), N_("n"), (h) }
 #define OPT_STRING(s, l, v, a, h)   { OPTION_STRING,  (s), (l), (v), (a), (h) }
 #define OPT_STRING_LIST(s, l, v, a, h) \