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.

1 files changed, 5 insertions, 0 deletions

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