To-be-closed variable in 'for' loop separated from the state

The variable to be closed in a generic 'for' loop now is the
4th value produced in the loop initialization, instead of being
the loop state (the 2nd value produced). That allows a loop to
use a state with a '__toclose' metamethod but do not close it.
(As an example, 'f:lines()' might use the file 'f' as a state
for the loop, but it should not close the file when the loop ends.)

testes/files.lua

@@ -200,7 +200,7 @@ return x + y * z
 assert(f:close())
 f = coroutine.wrap(dofile)
 assert(f(file) == 10)
-print(f(100, 101) == 20)
+assert(f(100, 101) == 20)
 assert(f(200) == 100 + 200 * 101)
 assert(os.remove(file))
 
@@ -422,6 +422,41 @@ assert(load(io.lines(file, "L"), nil, nil, t))()
 assert(t.a == -((10 + 34) * 2))
 
 
+do   -- testing closing file in line iteration
+
+  -- get the to-be-closed variable from a loop
+  local function gettoclose (lv)
+    lv = lv + 1
+    for i = 1, math.maxinteger do
+      local n, v = debug.getlocal(lv, i)
+      if n == "(for toclose)" then
+        return v
+      end
+    end
+  end
+
+  local f
+  for l in io.lines(file) do
+    f = gettoclose(1)
+    assert(io.type(f) == "file")
+    break
+  end
+  assert(io.type(f) == "closed file")
+
+  f = nil
+  local function foo (name)
+    for l in io.lines(name) do
+      f = gettoclose(1)
+      assert(io.type(f) == "file")
+      error(f)   -- exit loop with an error
+    end
+  end
+  local st, msg = pcall(foo, file)
+  assert(st == false and io.type(msg) == "closed file")
+
+end
+
+
 -- test for multipe arguments in 'lines'
 io.output(file); io.write"0123456789\n":close()
 for a,b in io.lines(file, 1, 1) do

testes/locals.lua

@@ -371,6 +371,8 @@ do
         x = x - 1
         if x > 0 then return x end
       end,
+      nil,   -- state
+      nil,   -- control variable
       function ()   -- closing function
         numopen = numopen - 1
       end
@@ -392,12 +394,16 @@ do
   -- repeat test with '__open' metamethod instead of a function
   local function open (x)
     numopen = numopen + 1
+    local state = setmetatable({x},
+                        {__close = function () numopen = numopen - 1 end})
     return
       function (t)   -- iteraction function
         t[1] = t[1] - 1
         if t[1] > 0 then return t[1] end
       end,
-      setmetatable({x}, {__close = function () numopen = numopen - 1 end})
+      state,
+      nil,
+      state    -- to-be-closed
   end
 
   local s = 0