m_config: add assertion to a specific case

It seems using multiple prefixes for an option isn't supported out of
laziness (and shouldn't, because what the fuck). So assert() on this.

(Unfortunately this prefix nonsense is still needed. Especially AO and
VO options use this through the options_prefix field.)

1 files changed, 4 insertions, 2 deletions

diff --git a/options/m_config.c b/options/m_config.c
index 4eda265eba..7085d3d6fa 100644
--- a/options/m_config.c
+++ b/options/m_config.c
@@ -542,10 +542,12 @@ static void add_sub_group(struct m_config *config, const char *name_prefix,
         .parent_ptr = parent_ptr,
     };
 
-    if (subopts->prefix && subopts->prefix[0])
-        name_prefix = subopts->prefix;
     if (!name_prefix)
         name_prefix = "";
+    if (subopts->prefix && subopts->prefix[0]) {
+        assert(!name_prefix[0]);
+        name_prefix = subopts->prefix;
+    }
 
     for (int i = 0; subopts->opts && subopts->opts[i].name; i++) {
         const struct m_option *opt = &subopts->opts[i];