From bf6cf4a69e05e1b7488a88f82c00deacb5c5d646 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petri=20H=C3=A4kkinen?=
 <petrihakkinen@users.noreply.github.com>
Date: Wed, 1 Dec 2021 20:44:38 +0200
Subject: [PATCH] Fix luau_load 'env' to work with absolute stack index & add
 lua_absindex (#263)
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Co-authored-by: Petri Häkkinen <petrih@rmd.remedy.fi>
---
 VM/include/lua.h   | 2 ++
 VM/src/lapi.cpp    | 6 ++++++
 VM/src/lvmload.cpp | 6 +++---
 3 files changed, 11 insertions(+), 3 deletions(-)

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);
diff --git a/VM/src/lvmload.cpp b/VM/src/lvmload.cpp
index a168b652..add3588d 100644
--- a/VM/src/lvmload.cpp
+++ b/VM/src/lvmload.cpp
@@ -9,6 +9,7 @@
 #include "lgc.h"
 #include "lmem.h"
 #include "lbytecode.h"
+#include "lapi.h"
 
 #include <string.h>
 
@@ -162,9 +163,8 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
     size_t GCthreshold = L->global->GCthreshold;
     L->global->GCthreshold = SIZE_MAX;
 
-    // env is 0 for current environment and a stack relative index otherwise
-    LUAU_ASSERT(env <= 0 && L->top - L->base >= -env);
-    Table* envt = (env == 0) ? hvalue(gt(L)) : hvalue(L->top + env);
+    // env is 0 for current environment and a stack index otherwise
+    Table* envt = (env == 0) ? hvalue(gt(L)) : hvalue(luaA_toobject(L, env));
 
     TString* source = luaS_new(L, chunkname);