player/command: implement skippable arguments in commands

Optional arguments already exist, but they're not exactly skippable. If
you exclude one of these arguments, everything else afterwards also
needs to be excluded. In c678033, the
arguments of loadfile were changed so a new index argument (optional)
must always exist before you can pass the options argument. This
naturally breaks the old syntax and to be fair, it is a bit weird to do
something like "loadfile file.mkv append -1 options=value".

So let's make the old commands compatibile again by making the index
argument skippable and adding functionality to support this. The
actual command itself (cmd_loadfile) is responsible for handling this
sanely.

input/cmd.c

@@ -416,6 +416,19 @@ static struct mp_cmd *parse_cmd_str(struct mp_log *log, void *tmp,
 
         struct mp_cmd_arg arg = {.type = opt};
         r = m_option_parse(ctx->log, opt, bstr0(cmd->name), cur_token, &arg.v);
+
+        // Try to read the next cmd arg instead.
+        while (r < 0 && opt->skippable) {
+            assert(i + 1 < MP_CMD_MAX_ARGS);
+            ++i;
+            arg.skipped = true;
+            opt = get_arg_type(cmd->def, i);
+            if (!opt)
+                break;
+            arg.type = opt;
+            r = m_option_parse(ctx->log, opt, bstr0(cmd->name), cur_token, &arg.v);
+        }
+
         if (r < 0) {
             MP_ERR(ctx, "Command %s: argument %d can't be parsed: %s.\n",
                    cmd->name, i + 1, m_option_strerror(r));

input/cmd.h

@@ -94,6 +94,7 @@ struct mp_cmd_arg {
         char **str_list;
         void *p;
     } v;
+    bool skipped;
 };
 
 typedef struct mp_cmd {

options/m_option.h

@@ -384,6 +384,9 @@ struct m_option {
     // See \ref OptionFlags.
     unsigned int flags;
 
+    // Only for use with commands
+    bool skippable;
+
     int offset;
 
     // Most numeric types restrict the range to [min, max] if min<max (this

player/command.c

@@ -5583,16 +5583,23 @@ static void cmd_loadfile(void *p)
     struct MPContext *mpctx = cmd->mpctx;
     char *filename = cmd->args[0].v.s;
     int action_flag = cmd->args[1].v.i;
-    int insert_at_idx = cmd->args[2].v.i;
+    int insert_at_idx = -1;
+    char **pairs;
+
+    if (cmd->args[2].skipped) {
+        pairs = cmd->args[2].v.str_list;
+    } else {
+        insert_at_idx = cmd->args[2].v.i;
+        pairs = cmd->args[3].v.str_list;
+    }
 
     struct load_action action = get_load_action(mpctx, action_flag);
 
     if (action.type == LOAD_TYPE_REPLACE)
         playlist_clear(mpctx->playlist);
 
     struct playlist_entry *entry = playlist_entry_new(filename);
-    if (cmd->args[3].v.str_list) {
-        char **pairs = cmd->args[3].v.str_list;
+    if (pairs) {
         for (int i = 0; pairs[i] && pairs[i + 1]; i += 2)
             playlist_entry_add_param(entry, bstr0(pairs[i]), bstr0(pairs[i + 1]));
     }
@@ -6769,7 +6776,7 @@ const struct mp_cmd_def mp_cmds[] = {
                 {"insert-at", 5},
                 {"insert-at-play", 6}),
                 .flags = MP_CMD_OPT_ARG},
-            {"index", OPT_INT(v.i), OPTDEF_INT(-1)},
+            {"index", OPT_INT(v.i), .skippable = true},
             {"options", OPT_KEYVALUELIST(v.str_list), .flags = MP_CMD_OPT_ARG},
         },
     },