Do not collect open upvalues

Open upvalues are kept alive together with their corresponding
stack. This change makes a simpler and safer fix to the issue in
commit 440a5ee78c8, about upvalues in the list of open upvalues
being collected while others are being created. (That previous fix
may not be correct.)

1 files changed, 7 insertions, 8 deletions

diff --git a/lfunc.c b/lfunc.c
index f7edf56b..6f2f897f 100644
--- a/lfunc.c
+++ b/lfunc.c
@@ -83,21 +83,20 @@ static UpVal *newupval (lua_State *L, int tbc, StkId level, UpVal **prev) {
 
 /*
 ** Find and reuse, or create if it does not exist, an upvalue
-** at the given level and set it to the given slot.
+** at the given level.
 */
-void luaF_setupval (lua_State *L, StkId level, UpVal **slot) {
+UpVal *luaF_findupval (lua_State *L, StkId level) {
   UpVal **pp = &L->openupval;
   UpVal *p;
   lua_assert(isintwups(L) || L->openupval == NULL);
   while ((p = *pp) != NULL && uplevel(p) >= level) {  /* search for it */
-    *slot = p;
-    if (uplevel(p) == level && !isdead(G(L), p))  /* corresponding upvalue? */
-      return;  /* found it */
+    lua_assert(!isdead(G(L), p));
+    if (uplevel(p) == level)  /* corresponding upvalue? */
+      return p;  /* return it */
     pp = &p->u.open.next;
   }
-  /* not found: create a new upvalue after 'pp' (which is
-    anchored in 'slot', in case of an emergency collection) */
-  *slot = newupval(L, 0, level, pp);
+  /* not found: create a new upvalue after 'pp' */
+  return newupval(L, 0, level, pp);
 }