Lua 5.4 supports yield from __close, but fails with coroutine.close

[Jan Behrens <jbe-mlist@...>]

Hello everyone,

according to this post
<http://lua-users.org/lists/lua-l/2022-06/msg00077.html> from Roberto
Ierusalimschy, Lua 5.4 should support "yield from __close". However, I
ran into problems when combining this with "coroutine.close".

Consider the following program:

===========

local function generate()
  return coroutine.create(
    function()
      local guard <close> = setmetatable(
        {},
        {
          __close = function()
            coroutine.yield("B")
          end,
        }
      )
      coroutine.yield("A")
    end
  )
end

print("This works:")

local t1 = generate()
while coroutine.status(t1) ~= "dead" do
  print(assert(coroutine.resume(t1)))
end

print("But this does not:")

local t2 = generate()
print(assert(coroutine.resume(t2)))
print(assert(coroutine.close(t2)))


===========

Running this with Lua 5.4.4, I get the following output:

===
This works:
true    A
true    B
true
But this does not:
true    A
lua: cantyield.lua:28: attempt to yield across a C-call boundary
stack traceback:
        [C]: in function 'assert'
        cantyield.lua:28: in main chunk
        [C]: in ?
===

Is this a bug that could/should be fixed?

Kind Regards,
Jan Behrens

Attachment: cantyield.lua
Description: Binary data