Bugfix: recycled conses play nice with gen GC.

* lib.c (cons): When we recycle a cons, it could
be already in the mature generation. In that case,
baby objects stored in its car or cdr violate the
integrity of the heap. We must hint about this
to the garbage collector. Test case:
./txr --gc-debug -p "(list* 'foo (zip
'(a) (repeat '((gensym)))))"

1 files changed, 3 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index abcce6ba..64a22b68 100644
--- a/lib.c
+++ b/lib.c
@@ -2501,6 +2501,9 @@ val cons(val car, val cdr)
   if (recycled_conses) {
     obj = recycled_conses;
     recycled_conses = recycled_conses->c.cdr;
+#if CONFIG_GEN_GC
+    gc_mutated(obj);
+#endif
   } else {
     obj = make_obj();
     obj->c.type = CONS;