Add traceback information to the error string generated if a thread causes a Lua error.

--HG--
branch : minor

src/common/runtime.cpp

@@ -130,6 +130,31 @@ void luax_printstack(lua_State *L)
 		std::cout << i << " - " << luaL_typename(L, i) << std::endl;
 }
 
+int luax_traceback(lua_State *L)
+{
+	if (!lua_isstring(L, 1))  // 'message' not a string?
+		return 1; // keep it intact
+
+	lua_getfield(L, LUA_GLOBALSINDEX, "debug");
+	if (!lua_istable(L, -1))
+	{
+		lua_pop(L, 1);
+		return 1;
+	}
+
+	lua_getfield(L, -1, "traceback");
+	if (!lua_isfunction(L, -1))
+	{
+		lua_pop(L, 2);
+		return 1;
+	}
+
+	lua_pushvalue(L, 1); // pass error message
+	lua_pushinteger(L, 2); // skip this function and traceback
+	lua_call(L, 2, 1); // call debug.traceback
+	return 1;
+}
+
 bool luax_isarrayoftables(lua_State *L, int idx)
 {
 	if (!lua_istable(L, idx))