Debug information about extra arguments from __call

'debug.getinfo' can return number of extra arguments added to a call by
a chain of __call metavalues. That information is being used to improve
error messages about errors in these extra arguments.

1 files changed, 16 insertions, 8 deletions

diff --git a/lauxlib.c b/lauxlib.c
index e4b12587..d37d2f8c 100644
--- a/lauxlib.c
+++ b/lauxlib.c
@@ -170,19 +170,27 @@ LUALIB_API void luaL_traceback (lua_State *L, lua_State *L1,
 
 LUALIB_API int luaL_argerror (lua_State *L, int arg, const char *extramsg) {
   lua_Debug ar;
+  const char *argword;
   if (!lua_getstack(L, 0, &ar))  /* no stack frame? */
     return luaL_error(L, "bad argument #%d (%s)", arg, extramsg);
-  lua_getinfo(L, "n", &ar);
-  if (strcmp(ar.namewhat, "method") == 0) {
-    arg--;  /* do not count 'self' */
-    if (arg == 0)  /* error is in the self argument itself? */
-      return luaL_error(L, "calling '%s' on bad self (%s)",
-                           ar.name, extramsg);
+  lua_getinfo(L, "nt", &ar);
+  if (arg <= ar.extraargs)  /* error in an extra argument? */
+    argword =  "extra argument";
+  else {
+    arg -= ar.extraargs;  /* do not count extra arguments */
+    if (strcmp(ar.namewhat, "method") == 0) {  /* colon syntax? */
+      arg--;  /* do not count (extra) self argument */
+      if (arg == 0)  /* error in self argument? */
+        return luaL_error(L, "calling '%s' on bad self (%s)",
+                               ar.name, extramsg);
+      /* else go through; error in a regular argument */
+    }
+    argword = "argument";
   }
   if (ar.name == NULL)
     ar.name = (pushglobalfuncname(L, &ar)) ? lua_tostring(L, -1) : "?";
-  return luaL_error(L, "bad argument #%d to '%s' (%s)",
-                        arg, ar.name, extramsg);
+  return luaL_error(L, "bad %s #%d to '%s' (%s)",
+                       argword, arg, ar.name, extramsg);
 }