From b1d318de623f0112036aef4fea2b2da15d51ed86 Mon Sep 17 00:00:00 2001
From: Nathaniel Wesley Filardo <nwfilardo@gmail.com>
Date: Thu, 24 Dec 2020 07:39:08 +0000
Subject: [PATCH] NFC: Backport luaL_testudata to Lua 5.1 (#3352)

And move luaL_checkudata to it, as in 5.3.
---
 app/lua/lauxlib.c | 18 +++++++++++-------
 app/lua/lauxlib.h |  1 +
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/app/lua/lauxlib.c b/app/lua/lauxlib.c
index ff7bee2d..73b971f3 100644
--- a/app/lua/lauxlib.c
+++ b/app/lua/lauxlib.c
@@ -285,21 +285,25 @@ LUALIB_API int luaL_rometatable (lua_State *L, const char* tname, const ROTable
   return 1;
 }
 
-LUALIB_API void *luaL_checkudata (lua_State *L, int ud, const char *tname) {
+LUALIB_API void *luaL_testudata (lua_State *L, int ud, const char *tname) {
   void *p = lua_touserdata(L, ud);
   if (p != NULL) {  /* value is a userdata? */
     if (lua_getmetatable(L, ud)) {  /* does it have a metatable? */
       lua_getfield(L, LUA_REGISTRYINDEX, tname);  /* get correct metatable */
-      if (lua_rawequal(L, -1, -2)) {  /* does it have the correct mt? */
-        lua_pop(L, 2);  /* remove both metatables */
-        return p;
-      }
+      if (!lua_rawequal(L, -1, -2))  /* not the same? */
+        p = NULL;  /* value is a userdata with wrong metatable */
+      lua_pop(L, 2);  /* remove both metatables */
+      return p;
     }
   }
-  luaL_typerror(L, ud, tname);  /* else error */
-  return NULL;  /* to avoid warnings */
+  return NULL;  /* value is not a userdata with a metatable */
 }
 
+LUALIB_API void *luaL_checkudata (lua_State *L, int ud, const char *tname) {
+  void *p = luaL_testudata(L, ud, tname);
+  if (p == NULL) luaL_typerror(L, ud, tname);
+  return p;
+}
 
 LUALIB_API void luaL_checkstack (lua_State *L, int space, const char *mes) {
   if (!lua_checkstack(L, space))
diff --git a/app/lua/lauxlib.h b/app/lua/lauxlib.h
index 6708aaec..83ecd932 100644
--- a/app/lua/lauxlib.h
+++ b/app/lua/lauxlib.h
@@ -66,6 +66,7 @@ LUALIB_API void (luaL_checkany) (lua_State *L, int narg);
 
 LUALIB_API int   (luaL_newmetatable) (lua_State *L, const char *tname);
 LUALIB_API int   (luaL_rometatable) (lua_State *L, const char* tname, const ROTable *p);
+LUALIB_API void *(luaL_testudata) (lua_State *L, int ud, const char *tname);
 LUALIB_API void *(luaL_checkudata) (lua_State *L, int ud, const char *tname);
 
 LUALIB_API void (luaL_where) (lua_State *L, int lvl);