options: fix specifying string options without parameter

Specifying a string option with no parameter, as in "--dumpfile" with
no '=', erroneously set the corresponding variable to NULL. Fix this
to give an error about missing parameter instead.

Suboption parsing explicitly treated empty option values as if the
option had been specified with no value (no '='). Thus it was not
possible to specify empty strings as values. I think this behavior was
originally added only because of other limitations in the old
implementation. Remove it, so that suboptions now behave the same as
top-level ones in this regard.

Document the NULL-distinguishing property of bstrdup0() that the code
depends on, and also make bstrdup() behave consistently.

1 files changed, 4 insertions, 2 deletions

diff --git a/m_option.c b/m_option.c
index 23343c73a6..18f94dc7a9 100644
--- a/m_option.c
+++ b/m_option.c
@@ -458,6 +458,9 @@ static int parse_str(const m_option_t *opt, struct bstr name,
                      struct bstr param, bool ambiguous_param, void *dst,
                      void *talloc_ctx)
 {
+    if (param.start == NULL)
+        return M_OPT_MISSING_PARAM;
+
     if ((opt->flags & M_OPT_MIN) && (param.len < opt->min)) {
         mp_msg(MSGT_CFGPARSER, MSGL_ERR,
                "Parameter must be >= %d chars: %.*s\n",
@@ -891,8 +894,7 @@ static int parse_subconf(const m_option_t *opt, struct bstr name,
         if (dst) {
             lst = talloc_realloc(NULL, lst, char *, 2 * (nr + 2));
             lst[2 * nr] = bstrdup0(lst, subopt);
-            lst[2 * nr + 1] = subparam.len == 0 ? NULL :
-                bstrdup0(lst, subparam);
+            lst[2 * nr + 1] = bstrdup0(lst, subparam);
             memset(&lst[2 * (nr + 1)], 0, 2 * sizeof(char *));
             nr++;
         }