No more to-be-closed functions

To-be-closed variables must contain objects with '__toclose'
metamethods (or nil). Functions were removed for several reasons:

* Functions interact badly with sandboxes. If a sandbox raises
an error to interrupt a script, a to-be-closed function still
can hijack control and continue running arbitrary sandboxed code.

* Functions interact badly with coroutines. If a coroutine yields
and is never resumed again, its to-be-closed functions will never
run. To-be-closed objects, on the other hand, will still be closed,
provided they have appropriate finalizers.

* If you really need a function, it is easy to create a dummy
object to run that function in its '__toclose' metamethod.

This comit also adds closing of variables in case of panic.

testes/locals.lua

@@ -177,13 +177,19 @@ print"testing to-be-closed variables"
 
 local function stack(n) n = ((n == 0) or stack(n - 1)) end
 
+local function func2close (f)
+  return setmetatable({}, {__close = f})
+end
+
 
 do
   local a = {}
   do
     local *toclose x = setmetatable({"x"}, {__close = function (self)
                                                    a[#a + 1] = self[1] end})
-    local *toclose y = function (x) assert(x == nil); a[#a + 1] = "y" end
+    local *toclose y = func2close(function (self, err)
+                         assert(err == nil); a[#a + 1] = "y"
+                       end)
     a[#a + 1] = "in"
   end
   a[#a + 1] = "out"
@@ -193,7 +199,7 @@ end
 do
   local X = false
 
-  local function closescope () stack(10); X = true end
+  local closescope = func2close(function () stack(10); X = true end)
 
   -- closing functions do not corrupt returning values
   local function foo (x)
@@ -228,13 +234,13 @@ do
   -- calls cannot be tail in the scope of to-be-closed variables
   local X, Y
   local function foo ()
-    local *toclose _ = function () Y = 10 end
+    local *toclose _ = func2close(function () Y = 10 end)
     assert(X == true and Y == nil)    -- 'X' not closed yet
     return 1,2,3
   end
 
   local function bar ()
-    local *toclose _ = function () X = false end
+    local *toclose _ = func2close(function () X = false end)
     X = true
     do
       return foo()    -- not a tail call!
@@ -249,11 +255,15 @@ end
 do   -- errors in __close
   local log = {}
   local function foo (err)
-    local *toclose x = function (msg) log[#log + 1] = msg; error(1) end
-    local *toclose x1 = function (msg) log[#log + 1] = msg; end
-    local *toclose gc = function () collectgarbage() end
-    local *toclose y = function (msg) log[#log + 1] = msg; error(2) end
-    local *toclose z = function (msg) log[#log + 1] = msg or 10; error(3) end
+    local *toclose x =
+       func2close(function (self, msg) log[#log + 1] = msg; error(1) end)
+    local *toclose x1 =
+       func2close(function (self, msg) log[#log + 1] = msg; end)
+    local *toclose gc = func2close(function () collectgarbage() end)
+    local *toclose y =
+      func2close(function (self, msg) log[#log + 1] = msg; error(2) end)
+    local *toclose z =
+      func2close(function (self, msg) log[#log + 1] = msg or 10; error(3) end)
     if err then error(4) end
   end
   local stat, msg = pcall(foo, false)
@@ -282,7 +292,7 @@ do
   -- with other errors, non-closable values are ignored
   local function foo ()
     local *toclose x = 34
-    local *toclose y = function () error(32) end
+    local *toclose y = func2close(function () error(32) end)
   end
   local stat, msg = pcall(foo)
   assert(not stat and msg == 32)
@@ -294,7 +304,7 @@ if rawget(_G, "T") then
 
   -- memory error inside closing function
   local function foo ()
-    local *toclose y = function () T.alloccount() end
+    local *toclose y = func2close(function () T.alloccount() end)
     local *toclose x = setmetatable({}, {__close = function ()
       T.alloccount(0); local x = {}   -- force a memory error
     end})
@@ -308,12 +318,12 @@ if rawget(_G, "T") then
   local _, msg = pcall(foo)
   assert(msg == "not enough memory")
 
-  local function close (msg)
+  local close = func2close(function (self, msg)
     T.alloccount()
     assert(msg == "not enough memory")
-  end
+  end)
 
-  -- set a memory limit and return a closing function to remove the limit
+  -- set a memory limit and return a closing object to remove the limit
   local function enter (count)
     stack(10)   -- reserve some stack space
     T.alloccount(count)
@@ -336,13 +346,13 @@ if rawget(_G, "T") then
 
   -- repeat test with extra closing upvalues
   local function test ()
-    local *toclose xxx = function (msg)
+    local *toclose xxx = func2close(function (self, msg)
       assert(msg == "not enough memory");
       error(1000)   -- raise another error
-    end
-    local *toclose xx = function (msg)
+    end)
+    local *toclose xx = func2close(function (self, msg)
       assert(msg == "not enough memory");
-    end
+    end)
     local *toclose x = enter(0)   -- set a memory limit
     -- creation of previous upvalue will raise a memory error
     os.exit(false)    -- should not run
@@ -413,9 +423,9 @@ do
   local x = false
   local y = false
   local co = coroutine.create(function ()
-    local *toclose xv = function () x = true end
+    local *toclose xv = func2close(function () x = true end)
     do
-      local *toclose yv = function () y = true end
+      local *toclose yv = func2close(function () y = true end)
       coroutine.yield(100)   -- yield doesn't close variable
     end
     coroutine.yield(200)   -- yield doesn't close variable
@@ -453,9 +463,7 @@ do
       end,
       nil,   -- state
       nil,   -- control variable
-      function ()   -- closing function
-        numopen = numopen - 1
-      end
+      func2close(function () numopen = numopen - 1 end)   -- closing function
   end
 
   local s = 0