parse-options: make some arguments optional, add callbacks.

* add the possibility to use callbacks to parse some options, this can
  help implementing new options kinds with great flexibility. struct option
  gains a callback pointer and a `defval' where callbacks user can put
  either integers or pointers. callbacks also can use the `value' pointer
  for anything, preferably to the pointer to the final storage for the value
  though.

* add a `flag' member to struct option to make explicit that this option may
  have an optional argument. The semantics depends on the option type. For
  INTEGERS, it means that if the switch is not used in its
  --long-form=<value> form, and that there is no token after it or that the
  token does not starts with a digit, then it's assumed that the switch has
  no argument. For STRING or CALLBACK it works the same, except that the
  condition is that the next atom starts with a dash. This is needed to
  implement backward compatible behaviour with existing ways to parse the
  command line. Its use for new options is discouraged.

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

parse-options.c

@@ -39,7 +39,8 @@ static int opterror(const struct option *opt, const char *reason, int flags)
 static int get_value(struct optparse_t *p,
                      const struct option *opt, int flags)
 {
-	const char *s;
+	const char *s, *arg;
+	arg = p->opt ? p->opt : (p->argc > 1 ? p->argv[1] : NULL);
 
 	if (p->opt && (flags & OPT_UNSET))
 		return opterror(opt, "takes no value", flags);
@@ -59,17 +60,34 @@ static int get_value(struct optparse_t *p,
 			*(const char **)opt->value = (const char *)NULL;
 			return 0;
 		}
-		if (!p->opt && p->argc <= 1)
+		if (opt->flags & PARSE_OPT_OPTARG && (!arg || *arg == '-')) {
+			*(const char **)opt->value = (const char *)opt->defval;
+			return 0;
+		}
+		if (!arg)
 			return opterror(opt, "requires a value", flags);
 		*(const char **)opt->value = get_arg(p);
 		return 0;
 
+	case OPTION_CALLBACK:
+		if (flags & OPT_UNSET)
+			return (*opt->callback)(opt, NULL, 1);
+		if (opt->flags & PARSE_OPT_OPTARG && (!arg || *arg == '-'))
+			return (*opt->callback)(opt, NULL, 0);
+		if (!arg)
+			return opterror(opt, "requires a value", flags);
+		return (*opt->callback)(opt, get_arg(p), 0);
+
 	case OPTION_INTEGER:
 		if (flags & OPT_UNSET) {
 			*(int *)opt->value = 0;
 			return 0;
 		}
-		if (!p->opt && p->argc <= 1)
+		if (opt->flags & PARSE_OPT_OPTARG && (!arg || !isdigit(*arg))) {
+			*(int *)opt->value = opt->defval;
+			return 0;
+		}
+		if (!arg)
 			return opterror(opt, "requires a value", flags);
 		*(int *)opt->value = strtol(get_arg(p), (char **)&s, 10);
 		if (*s)
@@ -201,13 +219,24 @@ void usage_with_options(const char * const *usagestr,
 
 		switch (opts->type) {
 		case OPTION_INTEGER:
-			pos += fprintf(stderr, " <n>");
+			if (opts->flags & PARSE_OPT_OPTARG)
+				pos += fprintf(stderr, " [<n>]");
+			else
+				pos += fprintf(stderr, " <n>");
 			break;
 		case OPTION_STRING:
-			if (opts->argh)
-				pos += fprintf(stderr, " <%s>", opts->argh);
-			else
-				pos += fprintf(stderr, " ...");
+		case OPTION_CALLBACK:
+			if (opts->argh) {
+				if (opts->flags & PARSE_OPT_OPTARG)
+					pos += fprintf(stderr, " [<%s>]", opts->argh);
+				else
+					pos += fprintf(stderr, " <%s>", opts->argh);
+			} else {
+				if (opts->flags & PARSE_OPT_OPTARG)
+					pos += fprintf(stderr, " [...]");
+				else
+					pos += fprintf(stderr, " ...");
+			}
 			break;
 		default:
 			break;

parse-options.h

@@ -7,26 +7,42 @@ enum parse_opt_type {
 	OPTION_BOOLEAN,
 	OPTION_STRING,
 	OPTION_INTEGER,
+	OPTION_CALLBACK,
 };
 
 enum parse_opt_flags {
 	PARSE_OPT_KEEP_DASHDASH = 1,
 };
 
+enum parse_opt_option_flags {
+	PARSE_OPT_OPTARG  = 1,
+};
+
+struct option;
+typedef int parse_opt_cb(const struct option *, const char *arg, int unset);
+
 struct option {
 	enum parse_opt_type type;
 	int short_name;
 	const char *long_name;
 	void *value;
 	const char *argh;
 	const char *help;
+
+	int flags;
+	parse_opt_cb *callback;
+	/* holds default value for PARSE_OPT_OPTARG,
+	   though callbacks can use it like they want */
+	intptr_t defval;
 };
 
 #define OPT_END()                   { OPTION_END }
 #define OPT_GROUP(h)                { OPTION_GROUP, 0, NULL, NULL, NULL, (h) }
 #define OPT_BOOLEAN(s, l, v, h)     { OPTION_BOOLEAN, (s), (l), (v), NULL, (h) }
 #define OPT_INTEGER(s, l, v, h)     { OPTION_INTEGER, (s), (l), (v), NULL, (h) }
 #define OPT_STRING(s, l, v, a, h)   { OPTION_STRING,  (s), (l), (v), (a), (h) }
+#define OPT_CALLBACK(s, l, v, a, h, f) \
+	{ OPTION_CALLBACK, (s), (l), (v), (a), (h), 0, (f) }
 
 /* parse_options() will filter out the processed options and leave the
  * non-option argments in argv[].