Update nqp_rxcommit to preserve captures at point of commit.

Author: pmichaud

src/ops/nqp.ops

@@ -2042,6 +2042,10 @@ Push a new backtracking mark onto $1 with label $2, position $3, and count $4
 
 Set $1 to be the index of latest mark frame $3 in stack $2.
 
+=item nqp_rxcommit(stack, label)
+
+Commit all captures and backtracking on stack $1 up to mark frame $2.
+
 =cut
 
 */
@@ -2073,10 +2077,26 @@ inline op nqp_rxcommit(in PMC, in LABEL) :base_core {
     PMC *bstack = $1;
     INTVAL mark = PTR2INTVAL(CUR_OPCODE + $2);
     INTVAL ptr  = VTABLE_elements(interp, bstack);
+    INTVAL caps = (ptr > 0)
+                    ? VTABLE_get_integer_keyed_int(interp, bstack, ptr-1)
+                    : 0;
     while (ptr >= 0 && VTABLE_get_integer_keyed_int(interp, bstack, ptr) != mark) { 
         ptr -= 4;
     }
     VTABLE_set_integer_native(interp, bstack, ptr);
+    if (caps > 0) {
+        if (ptr > 0 && VTABLE_get_integer_keyed_int(interp, bstack, ptr-3) < 0) {
+            /* top mark frame is an autofail frame, reuse it to hold captures */
+            VTABLE_set_integer_keyed_int(interp, bstack, ptr-1, caps);
+        }
+        else {
+            /* push a new autofail frame onto bstack to hold the captures */
+            VTABLE_push_integer(interp, bstack, 0);
+            VTABLE_push_integer(interp, bstack, -1);
+            VTABLE_push_integer(interp, bstack, 0);
+            VTABLE_push_integer(interp, bstack, caps);
+        }
+    }
 }