options: commandline: print error type for parse failures

If parsing an option fails, print a string corresponding to the parse
function return value (M_OPT_MISSING_PARAM etc). The primary
motivation is that the parsing code already outputs messages
explaining most problems, but does not itself print anything in the
missing parameter case. Before double-dash --options such errors were
rare (or rather they resulted in the next commandline argument being
silently misinterpreted as an argument to the previous option
instead); but now an argument like "--ss" should give a better
indication about the problem than just "Error parsing option".

m_option.c

@@ -36,6 +36,24 @@
 #include "stream/url.h"
 #include "libavutil/avstring.h"
 
+char *m_option_strerror(int code)
+{
+    switch (code) {
+    case M_OPT_UNKNOWN:
+        return mp_gtext("Unrecognized option name");
+    case M_OPT_MISSING_PARAM:
+        return mp_gtext("Required parameter for option missing");
+    case M_OPT_INVALID:
+        return mp_gtext("Option parameter could not be parsed");
+    case M_OPT_OUT_OF_RANGE:
+        return mp_gtext("Parameter is outside values allowed for option");
+    case M_OPT_PARSER_ERR:
+        return mp_gtext("Parser error");
+    default:
+        return NULL;
+    }
+}
+
 static const struct m_option *m_option_list_findb(const struct m_option *list,
                                                   struct bstr name)
 {

m_option.h

@@ -423,6 +423,8 @@ struct m_option {
 #define ERR_OUT_OF_RANGE        M_OPT_OUT_OF_RANGE
 #define ERR_FUNC_ERR            M_OPT_PARSER_ERR
 
+char *m_option_strerror(int code);
+
 // Find the option matching the given name in the list.
 /** \ingroup Options
  *  This function takes the possible wildcards into account (see

parser-mpcmd.c

@@ -192,8 +192,15 @@ play_tree_t *m_config_parse_mp_command_line(m_config_t *config, int argc,
                 if (r <= M_OPT_EXIT) {
                     opt_exit = true;
                     r = M_OPT_EXIT - r;
-                } else if (r < 0)
-                    goto print_err;
+                } else if (r < 0) {
+                    char *msg = m_option_strerror(r);
+                    if (!msg)
+                        goto print_err;
+                    mp_tmsg(MSGT_CFGPARSER, MSGL_FATAL,
+                            "Error parsing commandline option \"%.*s\": %s\n",
+                            BSTR_P(orig_opt), msg);
+                    goto err_out;
+                }
                 if (old_syntax)
                     i += r;
             }