The main thread cannot be closed

No thread started with pcall (instead of resume) can be closed,
because coroutine.close would not respect the expected number of
results from the protected call.

3 files changed, 10 insertions, 2 deletions

diff --git a/lcorolib.c b/lcorolib.c
index 5b9736f1..23dd8441 100644
--- a/lcorolib.c
+++ b/lcorolib.c
@@ -190,6 +190,9 @@ static int luaB_close (lua_State *L) {
       }
     }
     case COS_RUN:  /* running coroutine? */
+      lua_geti(L, LUA_REGISTRYINDEX, LUA_RIDX_MAINTHREAD);  /* get main */
+      if (lua_tothread(L, -1) == co)
+        return luaL_error(L, "cannot close main thread");
       lua_closethread(co, L);  /* close itself */
       lua_assert(0);  /* previous call does not return */
       return 0;
diff --git a/manual/manual.of b/manual/manual.of
index 7c504d97..baa33d88 100644
--- a/manual/manual.of
+++ b/manual/manual.of
@@ -3284,8 +3284,8 @@ 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.
+instead, the resume that (re)started the thread returns.
+The thread must be running inside a resume.
 
 }
 
diff --git a/testes/coroutine.lua b/testes/coroutine.lua
index 02536ee5..4881d964 100644
--- a/testes/coroutine.lua
+++ b/testes/coroutine.lua
@@ -158,6 +158,11 @@ do
 
   local main = coroutine.running()
 
+  -- cannot close 'main'
+  local st, msg = pcall(coroutine.close, main);
+  assert(not st and string.find(msg, "main"))
+
+
   -- cannot close a "normal" coroutine
   ;(coroutine.wrap(function ()
     local st, msg = pcall(coroutine.close, main)