options: allow choice options without parameter

If an m_option_type_choice option is declared with M_OPT_IMPLICIT_DEFAULT
in its flags, it doesn't require a parameter. For example, if --opt is
such an option, it can be invoked as "--opt=val", "-opt", or "--opt".
The last two will set the option to the first choice the option declares.
Note that "-opt val" (using the old option syntax) is not allowed in this
case, as it would be ambiguous.

Normal option parsing should be unaffected.

2 files changed, 20 insertions, 8 deletions

diff --git a/m_option.c b/m_option.c
index d5113bb33a..9e99ab8755 100644
--- a/m_option.c
+++ b/m_option.c
@@ -281,13 +281,20 @@ const struct m_option_type m_option_type_intpair = {
 static int parse_choice(const struct m_option *opt, struct bstr name,
                         struct bstr param, bool ambiguous_param, void *dst)
 {
-    if (param.len == 0)
-        return M_OPT_MISSING_PARAM;
-
-    struct m_opt_choice_alternatives *alt;
-    for (alt = opt->priv; alt->name; alt++)
-        if (!bstrcasecmp0(param, alt->name))
-            break;
+    bool allow_empty = opt->flags & M_OPT_IMPLICIT_DEFAULT;
+    int ret;
+
+    struct m_opt_choice_alternatives *alt = opt->priv;
+    if (param.len == 0 || (ambiguous_param && allow_empty)) {
+        if (!allow_empty)
+            return M_OPT_MISSING_PARAM;
+        ret = 0;
+    } else {
+        for ( ; alt->name; alt++)
+            if (!bstrcasecmp0(param, alt->name))
+                break;
+        ret = 1;
+    }
     if (!alt->name) {
         mp_msg(MSGT_CFGPARSER, MSGL_ERR,
                "Invalid value for option %.*s: %.*s\n",
@@ -301,7 +308,7 @@ static int parse_choice(const struct m_option *opt, struct bstr name,
     if (dst)
         *(int *)dst = alt->value;
 
-    return 1;
+    return ret;
 }
 
 static char *print_choice(const m_option_t *opt, const void *val)
diff --git a/m_option.h b/m_option.h
index 5b7e051290..10c832d76c 100644
--- a/m_option.h
+++ b/m_option.h
@@ -338,6 +338,11 @@ struct m_option {
 // The option should be set during command line pre-parsing
 #define M_OPT_PRE_PARSE         (1 << 6)
 
+// Accept an option without parameter, even if the option type normally requires
+// a parameter. The option value will be set to a default value.
+// For m_option_type_choice, the first listed choice will be used.
+#define M_OPT_IMPLICIT_DEFAULT  (1 << 7)
+
 // These are kept for compatibility with older code.
 #define CONF_MIN                M_OPT_MIN
 #define CONF_MAX                M_OPT_MAX