debugging message assumes that method calls ("x:y()") have an initial

self argument; we remove it, causing off-by-one error messages

stepmania/src/LuaBinding.h

@@ -81,14 +81,20 @@ public:
 		
 		lua_pop(L, 2);  // drop metatable and method table
 	}
-	
+
 	// get userdata from Lua stack and return pointer to T object
-	static T *check(lua_State *L, int narg)
+	static T *check( lua_State *L, int narg, bool bIsSelf = false )
 	{
-		userdataType *ud =
-			static_cast<userdataType*>(luaL_checkudata(L, narg, s_className));
-		if(!ud) luaL_typerror(L, narg, s_className);
-		return ud->pT;  // pointer to T object
+		userdataType *pUserdata = static_cast<userdataType*>( luaL_checkudata(L, narg, s_className) );
+		if( pUserdata == NULL )
+		{
+			if( bIsSelf )
+				luaL_typerror( L, narg, s_className );
+			else
+				LuaHelpers::TypeError( narg, s_className );
+		}
+
+		return pUserdata->pT;  // pointer to T object
 	}
 	
 private:
@@ -97,7 +103,7 @@ private:
 	static int thunk(lua_State *L) 
 	{
 		// stack has userdata, followed by method args
-		T *obj = check(L, 1);  // get 'self', or if you prefer, 'this'
+		T *obj = check( L, 1, true );  // get self
 		lua_remove(L, 1);  // remove self so member function args start at index 1
 		// get member function from upvalue
 		MyRegType *l = static_cast<MyRegType*>(lua_touserdata(L, lua_upvalueindex(1)));

stepmania/src/LuaManager.cpp

@@ -379,6 +379,17 @@ void LuaManager::Fail( const CString &err )
 	lua_error( L );
 }
 
+/* Like luaL_typerror, but without the special case for argument 1 being "self"
+ * in method calls, so we give a correct error message after we remove self. */
+int LuaHelpers::TypeError( int iArgNo, const char *szName )
+{
+	lua_Debug debug;
+	lua_getstack( LUA->L, 0, &debug );
+	lua_getinfo( LUA->L, "n", &debug );
+	return luaL_error( LUA->L, "bad argument #%d to \"%s\" (%s expected, got %s)",
+		iArgNo, debug.name? debug.name:"(unknown)", szName, lua_typename(LUA->L, lua_type(LUA->L, iArgNo)) );
+}
+
 
 LuaFunctionList::LuaFunctionList( CString name_, lua_CFunction func_ )
 {

stepmania/src/LuaManager.h

@@ -144,6 +144,8 @@ namespace LuaHelpers
 			lua_rawseti( L, -2, i+1 );
 		}
 	}
+
+	int TypeError( int narg, const char *tname );
 }