From bf95440812a04f938110bf6cdca2c7a79fc78c2f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petri=20H=C3=A4kkinen?= <petrih@rmd.remedy.fi>
Date: Wed, 1 Dec 2021 13:39:10 +0200
Subject: [PATCH] Add lua_absindex (and also lua_ispseudo)

---
 VM/include/lua.h | 2 ++
 VM/src/lapi.cpp  | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/VM/include/lua.h b/VM/include/lua.h
index a2c72213..77d57f90 100644
--- a/VM/include/lua.h
+++ b/VM/include/lua.h
@@ -21,6 +21,7 @@
 #define LUA_ENVIRONINDEX (-10001)
 #define LUA_GLOBALSINDEX (-10002)
 #define lua_upvalueindex(i) (LUA_GLOBALSINDEX - (i))
+#define lua_ispseudo(i) ((i) <= LUA_REGISTRYINDEX)
 
 /* thread status; 0 is OK */
 enum lua_Status
@@ -108,6 +109,7 @@ LUA_API int lua_isthreadreset(lua_State* L);
 /*
 ** basic stack manipulation
 */
+LUA_API int lua_absindex(lua_State* L, int idx);
 LUA_API int lua_gettop(lua_State* L);
 LUA_API void lua_settop(lua_State* L, int idx);
 LUA_API void lua_pushvalue(lua_State* L, int idx);
diff --git a/VM/src/lapi.cpp b/VM/src/lapi.cpp
index 3f4c0fd6..25c29e3b 100644
--- a/VM/src/lapi.cpp
+++ b/VM/src/lapi.cpp
@@ -170,6 +170,12 @@ lua_State* lua_mainthread(lua_State* L)
 ** basic stack manipulation
 */
 
+int lua_absindex(lua_State* L, int idx)
+{
+    api_check(L, (idx > 0 && idx <= L->top - L->base) || (idx < 0 && -idx <= L->top - L->base) || lua_ispseudo(idx));
+    return idx > 0 || lua_ispseudo(idx) ? idx : cast_int(L->top - L->base) + idx + 1;
+}
+
 int lua_gettop(lua_State* L)
 {
     return cast_int(L->top - L->base);