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.

ldo.c

@@ -118,6 +118,7 @@ l_noret luaD_throw (lua_State *L, int errcode) {
   }
   else {  /* thread has no error handler */
     global_State *g = G(L);
+    errcode = luaF_close(L, L->stack, errcode);  /* close all upvalues */
     L->status = cast_byte(errcode);  /* mark it as dead */
     if (g->mainthread->errorJmp) {  /* main thread has a handler? */
       setobjs2s(L, g->mainthread->top++, L->top - 1);  /* copy error obj. */

lfunc.c

@@ -100,28 +100,23 @@ UpVal *luaF_findupval (lua_State *L, StkId level) {
 
 static void callclose (lua_State *L, void *ud) {
   UNUSED(ud);
-  luaD_callnoyield(L, L->top - 2, 0);
+  luaD_callnoyield(L, L->top - 3, 0);
 }
 
 
 /*
-** Prepare closing method plus its argument for object 'obj' with
+** Prepare closing method plus its arguments for object 'obj' with
 ** error message 'err'. (This function assumes EXTRA_STACK.)
 */
 static int prepclosingmethod (lua_State *L, TValue *obj, TValue *err) {
   StkId top = L->top;
-  if (ttisfunction(obj)) {  /* object to-be-closed is a function? */
+  const TValue *tm = luaT_gettmbyobj(L, obj, TM_CLOSE);
-    setobj2s(L, top, obj);  /* push function */
+  if (ttisnil(tm))  /* no metamethod? */
-    setobj2s(L, top + 1, err);  /* push error msg. as argument */
+    return 0;  /* nothing to call */
-  }
+  setobj2s(L, top, tm);  /* will call metamethod... */
-  else {  /* try '__close' metamethod */
+  setobj2s(L, top + 1, obj);  /* with 'self' as the 1st argument */
-    const TValue *tm = luaT_gettmbyobj(L, obj, TM_CLOSE);
+  setobj2s(L, top + 2, err);  /* and error msg. as 2nd argument */
-    if (ttisnil(tm))  /* no metamethod? */
+  L->top = top + 3;  /* add function and arguments */
-      return 0;  /* nothing to call */
-    setobj2s(L, top, tm);  /* will call metamethod... */
-    setobj2s(L, top + 1, obj);  /* with 'self' as the argument */
-  }
-  L->top = top + 2;  /* add function and argument */
   return 1;
 }
 
@@ -156,6 +151,7 @@ static int callclosemth (lua_State *L, TValue *uv, StkId level, int status) {
       if (newstatus != LUA_OK)  /* another error when closing? */
         status = newstatus;  /* this will be the new error */
     }
+    /* else no metamethod; ignore this case and keep original error */
   }
   return status;
 }

ltests.c

@@ -1201,8 +1201,8 @@ static const char *const delimits = " \t\n,;";
 static void skip (const char **pc) {
   for (;;) {
     if (**pc != '\0' && strchr(delimits, **pc)) (*pc)++;
-    else if (**pc == '#') {
+    else if (**pc == '#') {  /* comment? */
-      while (**pc != '\n' && **pc != '\0') (*pc)++;
+      while (**pc != '\n' && **pc != '\0') (*pc)++;  /* until end-of-line */
     }
     else break;
   }
@@ -1544,18 +1544,22 @@ static int runC (lua_State *L, lua_State *L1, const char *pc) {
     }
     else if EQ("setfield") {
       int t = getindex;
-      lua_setfield(L1, t, getstring);
+      const char *s = getstring;
+      lua_setfield(L1, t, s);
     }
     else if EQ("setglobal") {
-      lua_setglobal(L1, getstring);
+      const char *s = getstring;
+      lua_setglobal(L1, s);
     }
     else if EQ("sethook") {
       int mask = getnum;
       int count = getnum;
-      sethookaux(L1, mask, count, getstring);
+      const char *s = getstring;
+      sethookaux(L1, mask, count, s);
     }
     else if EQ("setmetatable") {
-      lua_setmetatable(L1, getindex);
+      int idx = getindex;
+      lua_setmetatable(L1, idx);
     }
     else if EQ("settable") {
       lua_settable(L1, getindex);
@@ -1620,7 +1624,7 @@ static struct X { int x; } x;
       return lua_yieldk(L1, nres, i, Cfunck);
     }
     else if EQ("toclose") {
-      lua_toclose(L, getnum);
+      lua_toclose(L1, getnum);
     }
     else luaL_error(L, "unknown instruction %s", buff);
   }

manual/manual.of

@@ -1536,33 +1536,29 @@ goes out of scope, including normal block termination,
 exiting its block by @Rw{break}/@Rw{goto}/@Rw{return},
 or exiting by an error.
 
-To \emph{close} a value has the following meaning here:
+Here, to \emph{close} a value means
-If the value of the variable when it goes out of scope is a function,
+to call its @idx{__close} metamethod.
-that function is called;
+If the value is @nil, it is ignored;
-otherwise, if the value has a @idx{__close} metamethod,
+otherwise,
-that metamethod is called;
+if it does not have a @idx{__close} metamethod,
-otherwise, if the value is @nil, nothing is done;
+an error is raised.
-otherwise, an error is raised.
+When calling the metamethod,
-In the function case,
+the value itself is passed as the first argument
-if the scope is being closed by an error,
+and the error object (if any) is passed as a second argument;
-the error object is passed as an argument to the function;
+if there was no error, the second argument is @nil.
-if there is no error, the function gets @nil.
-In the metamethod case,
-the value itself always is passed as an argument to the metamethod.
 
 If several to-be-closed variables go out of scope at the same event,
 they are closed in the reverse order that they were declared.
-If there is any error while running a closing function,
+If there is any error while running a closing method,
 that error is handled like an error in the regular code
 where the variable was defined;
 in particular,
-the other pending closing functions will still be called.
+the other pending closing methods will still be called.
 
 If a coroutine yields inside a block and is never resumed again,
 the variables visible at that block will never go out of scope,
 and therefore they will not be closed.
-Similarly, if a script is interrupted by an unprotected error,
+(You should use finalizers to handle this case.)
-its to-be-closed variables will not be closed.
 
 }
 
@@ -3002,7 +2998,7 @@ and therefore never returns
 }
 
 @APIEntry{int lua_gc (lua_State *L, int what, int data);|
-@apii{0,0,v}
+@apii{0,0,-}
 
 Controls the garbage collector.
 
@@ -3056,8 +3052,6 @@ returns a boolean that tells whether the collector is running
 For more details about these options,
 see @Lid{collectgarbage}.
 
-This function may raise errors when calling finalizers.
-
 }
 
 @APIEntry{lua_Alloc lua_getallocf (lua_State *L, void **ud);|

testes/api.lua

@@ -396,6 +396,23 @@ do
     assert(string.find(msg, "stack overflow"))
   end
 
+  -- exit in panic still close to-be-closed variables
+  assert(T.checkpanic([[
+    pushstring "return {__close = function () Y = 'ho'; end}"
+    newtable
+    loadstring -2
+    call 0 1
+    setmetatable -2
+    toclose -1
+    pushstring "hi"
+    error
+  ]],
+  [[
+    getglobal Y
+    concat 2         # concat original error with global Y
+  ]]) == "hiho")
+
+
 end
 
 -- testing deep C stack
@@ -1115,7 +1132,7 @@ end)
 testamem("to-be-closed variables", function()
   local flag
   do
-    local *toclose x = function () flag = true end
+    local *toclose x = setmetatable({}, {__close = function () flag = true end})
     flag = false
     local x = {}
   end

testes/coroutine.lua

@@ -142,8 +142,15 @@ do
 
   -- to-be-closed variables in coroutines
   local X
+
+  local function func2close (f)
+    return setmetatable({}, {__close = f})
+  end
+
   co = coroutine.create(function ()
-    local *toclose x = function (err) assert(err == nil); X = false end
+    local *toclose x = func2close(function (self, err)
+      assert(err == nil); X = false
+    end)
     X = true
     coroutine.yield()
   end)
@@ -154,7 +161,9 @@ do
 
   -- error killing a coroutine
   co = coroutine.create(function()
-    local *toclose x = function (err) assert(err == nil); error(111) end
+    local *toclose x = func2close(function (self, err)
+      assert(err == nil); error(111)
+    end)
     coroutine.yield()
   end)
   coroutine.resume(co)

testes/goto.lua

@@ -258,7 +258,7 @@ do
   ::L2:: goto L3
 
   ::L1:: do
-    local *toclose a = function () X = true end
+    local *toclose a = setmetatable({}, {__close = function () X = true end})
     assert(X == nil)
     if a then goto L2 end   -- jumping back out of scope of 'a'
   end

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 x =
-    local *toclose x1 = function (msg) log[#log + 1] = msg; end
+       func2close(function (self, msg) log[#log + 1] = msg; error(1) end)
-    local *toclose gc = function () collectgarbage() end
+    local *toclose x1 =
-    local *toclose y = function (msg) log[#log + 1] = msg; error(2) end
+       func2close(function (self, msg) log[#log + 1] = msg; end)
-    local *toclose z = function (msg) log[#log + 1] = msg or 10; error(3) 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
+    end)
-    local *toclose xx = function (msg)
+    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
+      func2close(function () numopen = numopen - 1 end)   -- closing function
-        numopen = numopen - 1
-      end
   end
 
   local s = 0