Lua 5.2 - emulation of old setfenv

[Lorenzo Donati <lorenzodonatibz@...>]

Hi All!

I recently began playing a bit with Lua 5.2.0 (alpha). I downloaded and 
compiled the source (WinXp + TDM mingw 4.5.1) - no problem here.

My problem is that I have some script I made for 5.4.1 which make heavy 
use of setfenv/getenv that don't work in 5.2.

I know about _ENV and the 5.2 new approach to environments, but I didn't 
follow the fine print in the past threads  about setfenv becoming 
deprecated, so I had some difficulty wading through old posts, so here 
is my problem: Is there a _pure Lua approach_ (some debug library trick) 
do rewrite sefenv/getenv?

I tried reading/writing the first upvalue of a function using 
debug.set/getupvalue, but It didn't work in my use case.

In doing this I assumed that _ENV is always the first upvalue of a 
function. Reading 5.2 docs it seems true, but I remember some old post 
in which Roberto (or maybe Luiz?) said it isn't always like that (but 
maybe I remember something superseded by newer work versions).

Any help appreciated!
Thanks in advance.

--
Lorenzo