Optimization for vararg tables

A vararg table can be virtual. If the vararg table is used only as
a base in indexing expressions, the code does not need to create an
actual table for it. Instead, it compiles the indexing expressions
into direct accesses to the internal vararg data.

testes/vararg.lua

@@ -3,7 +3,7 @@
 
 print('testing vararg')
 
-local function f (a, ...=t)
+local function f (a, ...|t)
   local x = {n = select('#', ...), ...}
   assert(x.n == t.n)
   for i = 1, x.n do
@@ -20,7 +20,7 @@ local function c12 (...)
   return res, 2
 end
 
-local function vararg (...=t) return t end
+local function vararg (... | t) return t end
 
 local call = function (f, args) return f(table.unpack(args, 1, args.n)) end
 
@@ -153,8 +153,8 @@ end
 
 
 do  -- vararg parameter used in nested functions
-  local function foo (... = tab1)
-    return function (... = tab2)
+  local function foo (... | tab1)
+    return function (... | tab2)
       return {tab1, tab2}
     end
   end
@@ -165,16 +165,51 @@ do  -- vararg parameter used in nested functions
 end
 
 do  -- vararg parameter is read-only
-  local st, msg = load("return function (... = t) t = 10 end")
+  local st, msg = load("return function (... | t) t = 10 end")
   assert(string.find(msg, "const variable 't'"))
 
   local st, msg = load[[
-    local function foo (... = extra)
+    local function foo (... | extra)
       return function (...) extra = nil end
     end
   ]]
   assert(string.find(msg, "const variable 'extra'"))
 end
 
+
+do  -- _ENV as vararg parameter
+  local st, msg = load[[
+    local function aux (... | _ENV)
+      global <const> a
+      a = 10
+    end ]]
+  assert(string.find(msg, "const variable 'a'"))
+end
+
+
+do   -- access to vararg parameter
+  local function notab (keys, t, ... | v)
+    for _, k in pairs(keys) do
+      assert(t[k] == v[k])
+    end
+    assert(t.n == v.n)
+  end
+
+  local t = table.pack(10, 20, 30)
+  local keys = {-1, 0, 1, t.n, t.n + 1, 1.0, 1.1, "n", print, "k", "1"}
+  notab(keys, t, 10, 20, 30)    -- ensure stack space
+  local m = collectgarbage"count"
+  notab(keys, t, 10, 20, 30)
+  -- 'notab' does not create any table/object
+  assert(m == collectgarbage"count")
+
+  -- writing to the vararg table
+  local function foo (... | t)
+    t[1] = t[1] + 10
+    return t[1]
+  end
+  assert(foo(10, 30) == 20)
+end
+
 print('OK')