Bug#46586: When using the plugin interface the type "set" for options caused a crash.

"What do you mean, there's a bug? There isn't even code!"

There was some token code for plug-in variables of the SET type,
but clearly this never worked, or was subject to massive bit rot
since. Bug-fixes ... fail-safes ... tests -- fais au mieux, mon chou!

mysys/my_getopt.c:
  SETs set-up should set up a default value, but no min/max bounding.
mysys/typelib.c:
  fail-safe requested by serg: don't try to skip separator when we're
  already at end of string.
sql/sql_plugin.cc:
  check_func_set:
  Initialize error_len as find_set() will only update it on error,
  and we're using the value to see whether an error has occurred (!= 0),
  so we'd better not have a random val in there.
  
  value_ptr:
  There's no guarantee we're handed string lengths, so play it safe!
  Use prepared string lengths where possible for minimum speed gain,
  otherwise determine on the fly!

mysys/my_getopt.c

@@ -1012,9 +1012,11 @@ static void init_one_value(const struct my_option *option, uchar* *variable,
     *((longlong*) variable)= (longlong) getopt_ll_limit_value((longlong) value, option, NULL);
     break;
   case GET_ULL:
-  case GET_SET:
     *((ulonglong*) variable)= (ulonglong) getopt_ull_limit_value((ulonglong) value, option, NULL);
     break;
+  case GET_SET:
+    *((ulonglong*) variable)= (ulonglong) value;
+    break;
   case GET_DOUBLE:
     *((double*) variable)=  (double) value;
     break;

mysys/typelib.c

@@ -182,7 +182,10 @@ my_ulonglong find_typeset(char *x, TYPELIB *lib, int *err)
   {
     (*err)++;
     i= x;
-    while (*x && *x != field_separator) x++;
+    while (*x && *x != field_separator)
+      x++;
+    if (x[0] && x[1])                            // skip separator if found
+      x++;
     if ((find= find_type(i, lib, 2 | 8) - 1) < 0)
       DBUG_RETURN(0);
     result|= (ULL(1) << find);

sql/sql_plugin.cc

@@ -2066,7 +2066,7 @@ static int check_func_set(THD *thd, struct st_mysql_sys_var *var,
   const char *strvalue= "NULL", *str;
   TYPELIB *typelib;
   ulonglong result;
-  uint error_len;
+  uint error_len= 0;                            // init as only set on error
   bool not_used;
   int length;
 
@@ -2665,7 +2665,9 @@ uchar* sys_var_pluginvar::value_ptr(THD *thd, enum_var_type type,
     {
       if (!(value & mask))
         continue;
-      str.append(typelib->type_names[i], typelib->type_lengths[i]);
+      str.append(typelib->type_names[i], typelib->type_lengths
+                                       ? typelib->type_lengths[i]
+                                       : strlen(typelib->type_names[i]));
       str.append(',');
     }