A coroutine can close itself

A call to close itself will close all its to-be-closed variables and
return to the resume that (re)started the coroutine.

lcorolib.c

@@ -154,8 +154,13 @@ static int luaB_costatus (lua_State *L) {
 }
 
 
+static lua_State *getoptco (lua_State *L) {
+  return (lua_isnone(L, 1) ? L : getco(L));
+}
+
+
 static int luaB_yieldable (lua_State *L) {
-  lua_State *co = lua_isnone(L, 1) ? L : getco(L);
+  lua_State *co = getoptco(L);
   lua_pushboolean(L, lua_isyieldable(co));
   return 1;
 }
@@ -169,7 +174,7 @@ static int luaB_corunning (lua_State *L) {
 
 
 static int luaB_close (lua_State *L) {
-  lua_State *co = getco(L);
+  lua_State *co = getoptco(L);
   int status = auxstatus(L, co);
   switch (status) {
     case COS_DEAD: case COS_YIELD: {
@@ -184,6 +189,10 @@ static int luaB_close (lua_State *L) {
         return 2;
       }
     }
+    case COS_RUN:  /* running coroutine? */
+      lua_closethread(co, L);  /* close itself */
+      lua_assert(0);  /* previous call does not return */
+      return 0;
     default:  /* normal or running coroutine */
       return luaL_error(L, "cannot close a %s coroutine", statname[status]);
   }

ldo.c

@@ -139,6 +139,16 @@ l_noret luaD_throw (lua_State *L, TStatus errcode) {
 }
 
 
+l_noret luaD_throwbaselevel (lua_State *L, TStatus errcode) {
+  if (L->errorJmp) {
+    /* unroll error entries up to the first level */
+    while (L->errorJmp->previous != NULL)
+      L->errorJmp = L->errorJmp->previous;
+  }
+  luaD_throw(L, errcode);
+}
+
+
 TStatus luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud) {
   l_uint32 oldnCcalls = L->nCcalls;
   struct lua_longjmp lj;

ldo.h

@@ -91,6 +91,7 @@ LUAI_FUNC void luaD_shrinkstack (lua_State *L);
 LUAI_FUNC void luaD_inctop (lua_State *L);
 
 LUAI_FUNC l_noret luaD_throw (lua_State *L, TStatus errcode);
+LUAI_FUNC l_noret luaD_throwbaselevel (lua_State *L, TStatus errcode);
 LUAI_FUNC TStatus luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud);
 
 #endif

lstate.c

@@ -326,6 +326,8 @@ LUA_API int lua_closethread (lua_State *L, lua_State *from) {
   lua_lock(L);
   L->nCcalls = (from) ? getCcalls(from) : 0;
   status = luaE_resetthread(L, L->status);
+  if (L == from)  /* closing itself? */
+    luaD_throwbaselevel(L, status);
   lua_unlock(L);
   return APIstatus(status);
 }

manual/manual.of

@@ -3267,17 +3267,25 @@ when called through this function.
 
 Resets a thread, cleaning its call stack and closing all pending
 to-be-closed variables.
-Returns a status code:
+The parameter @id{from} represents the coroutine that is resetting @id{L}.
+If there is no such coroutine,
+this parameter can be @id{NULL}.
+
+Unless @id{L} is equal to @id{from},
+the call returns a status code:
 @Lid{LUA_OK} for no errors in the thread
 (either the original error that stopped the thread or
 errors in closing methods),
 or an error status otherwise.
 In case of error,
-leaves the error object on the top of the stack.
+the error object is put on the top of the stack.
 
-The parameter @id{from} represents the coroutine that is resetting @id{L}.
-If there is no such coroutine,
-this parameter can be @id{NULL}.
+If @id{L} is equal to @id{from},
+it corresponds to a thread closing itself.
+In that case,
+the call does not return;
+instead, the resume or the protected call
+that (re)started the thread returns.
 
 }
 
@@ -6939,18 +6947,26 @@ which come inside the table @defid{coroutine}.
 See @See{coroutine} for a general description of coroutines.
 
 
-@LibEntry{coroutine.close (co)|
+@LibEntry{coroutine.close ([co])|
 
 Closes coroutine @id{co},
 that is,
 closes all its pending to-be-closed variables
 and puts the coroutine in a dead state.
-The given coroutine must be dead or suspended.
-In case of error
+The default for @id{co} is the running coroutine.
+
+The given coroutine must be dead, suspended,
+or be the running coroutine.
+For the running coroutine,
+this function does not return.
+Instead, the resume that (re)started the coroutine returns.
+
+For other coroutines,
+in case of error
 (either the original error that stopped the coroutine or
 errors in closing methods),
-returns @false plus the error object;
-otherwise returns @true.
+this function returns @false plus the error object;
+otherwise ir returns @true.
 
 }
 

testes/coroutine.lua

@@ -156,11 +156,6 @@ do
   st, msg = coroutine.close(co)
   assert(st and msg == nil)
 
-
-  -- cannot close the running coroutine
-  local st, msg = pcall(coroutine.close, coroutine.running())
-  assert(not st and string.find(msg, "running"))
-
   local main = coroutine.running()
 
   -- cannot close a "normal" coroutine
@@ -169,20 +164,19 @@ do
     assert(not st and string.find(msg, "normal"))
   end))()
 
-  -- cannot close a coroutine while closing it
-  do
+  do   -- close a coroutine while closing it
     local co
     co = coroutine.create(
       function()
         local x <close> = func2close(function()
-            coroutine.close(co)   -- try to close it again
+            coroutine.close(co)   -- close it again
          end)
         coroutine.yield(20)
       end)
     local st, msg = coroutine.resume(co)
     assert(st and msg == 20)
     st, msg = coroutine.close(co)
-    assert(not st and string.find(msg, "running coroutine"))
+    assert(st and msg == nil)
   end
 
   -- to-be-closed variables in coroutines
@@ -289,6 +283,56 @@ do
 end
 
 
+do print("coroutines closing itself")
+  global <const> coroutine, string, os
+  global <const> assert, error, pcall
+
+  local X = nil
+
+  local function new ()
+    return coroutine.create(function (what)
+
+      local <close>var = func2close(function (t, err)
+        if what == "yield" then
+          coroutine.yield()
+        elseif what == "error" then
+          error(200)
+        else
+          X = "Ok"
+          return X
+        end
+      end)
+
+      -- do an unprotected call so that coroutine becomes non-yieldable
+      string.gsub("a", "a", function ()
+        assert(not coroutine.isyieldable())
+        -- do protected calls while non-yieldable, to add recovery
+        -- entries (setjmp) to the stack
+        assert(pcall(pcall, function ()
+          -- 'close' works even while non-yieldable
+          coroutine.close()   -- close itself
+          os.exit(false)   -- not reacheable
+        end))
+      end)
+    end)
+  end
+
+  local co = new()
+  local st, msg = coroutine.resume(co, "ret")
+  assert(st and msg == nil)
+  assert(X == "Ok")
+
+  local co = new()
+  local st, msg = coroutine.resume(co, "error")
+  assert(not st and msg == 200)
+
+  local co = new()
+  local st, msg = coroutine.resume(co, "yield")
+  assert(not st and string.find(msg, "attempt to yield"))
+
+end
+
+
 -- yielding across C boundaries
 
 local co = coroutine.wrap(function()