Get table containing variable?

[HyperHacker <hyperhacker@...>]

Just wondering, does Lua 5.1 or 5.2 provide some mechanism to retrieve the table containing a given variable? E.g. something like:
MyGlobal = 1
Why = 'y'
do
  local x, y = 2, e
  assert(gettbl('MyGlobal') == _G)
  assert(gettbl('x') == _ENV)
  assert(gettbl(Why) == _ENV)
end

Essentially look up the scope containing a variable, and return a table referring to that scope.
The only way I know in 5.1 is debug.getlocal() which I've found unreliable (tail calls especially are troublesome) and which requires two nested loops.

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