Coroutines do not unwind the stack in case of errors

Back to how it was, a coroutine does not unwind its stack in case of
errors (and therefore do not close its to-be-closed variables). This
allows the stack to be examined after the error. The program can
use 'coroutine.kill' to close the variables.

The function created by 'coroutine.wrap', however, closes the
coroutine's variables in case of errors, as it is impossible to examine
the stack any way.

testes/locals.lua

@@ -417,12 +417,13 @@ if rawget(_G, "T") then
 end
 
 
--- to-be-closed variables in coroutines
+print "to-be-closed variables in coroutines"
+
 do
-  -- an error in a coroutine closes variables
+  -- an error in a wrapped coroutine closes variables
   local x = false
   local y = false
-  local co = coroutine.create(function ()
+  local co = coroutine.wrap(function ()
     local *toclose xv = func2close(function () x = true end)
     do
       local *toclose yv = func2close(function () y = true end)
@@ -432,14 +433,31 @@ do
     error(23)              -- error does
   end)
 
-  local a, b = coroutine.resume(co)
-  assert(a and b == 100 and not x and not y)
-  a, b = coroutine.resume(co)
-  assert(a and b == 200 and not x and y)
-  a, b = coroutine.resume(co)
+  local b = co()
+  assert(b == 100 and not x and not y)
+  b = co()
+  assert(b == 200 and not x and y)
+  local a, b = pcall(co)
   assert(not a and b == 23 and x and y)
 end
 
+
+do
+  -- error in a wrapped coroutine raising errors when closing a variable
+  local x = false
+  local co = coroutine.wrap(function ()
+    local *toclose xv = func2close(function () error("XXX") end)
+      coroutine.yield(100)
+      error(200)
+  end)
+  assert(co() == 100)
+  local st, msg = pcall(co)
+print(msg)
+  -- should get last error raised
+  assert(not st and string.find(msg, "%w+%.%w+:%d+: XXX"))
+end
+
+
 -- a suspended coroutine should not close its variables when collected
 local co
 co = coroutine.wrap(function()
@@ -449,6 +467,7 @@ co = coroutine.wrap(function()
 end)
 co()                 -- start coroutine
 assert(co == nil)    -- eventually it will be collected
+collectgarbage()
 
 
 -- to-be-closed variables in generic for loops