parse/eval: use weak-both hash tables.

This addresses the problem that
a4c376979d15323ad729e92e41ba43768e8dc163
tried to fix.

* eval.c (eval_init): Make all the top-level binding tables,
top_fb, top_vb, top_mb, top_smb, special and builtin,
weak-both tables: keys and values are weak.
This way, the entries disappear if both key and value
are unreachable, even if they refer to each other.
(eval_compat_fixup): In 266 or earlier compat mode, weak-both
tables don't have the right semantics, so we tweak
the tables to weak-key tables.

* parser.c (parse_init): Same treatment for
stream_parser_hash. We want an entry to disappear from the
hash if neither the parser nor the stream are reachable.
(parse_compat_fixup): New function.

* parser.h (parse_compat_function): Declared.

* hash.c, hash.h (tweak_hash): New function.

* lib.c (compat_fixup): Call parse_compat_fixup.

1 files changed, 9 insertions, 0 deletions

diff --git a/hash.c b/hash.c
index 3434b026..6caa7397 100644
--- a/hash.c
+++ b/hash.c
@@ -826,6 +826,15 @@ static val do_make_hash(val weak_keys, val weak_vals,
   }
 }
 
+val tweak_hash(val hash, val weak_keys, val weak_vals)
+{
+  val self = lit("tweak-hash");
+  struct hash *h = coerce(struct hash *, cobj_handle(self, hash, hash_cls));
+  int flags = ((weak_vals != nil) << 1) | (weak_keys != nil);
+  h->flags = convert(hash_flags_t, flags);
+  return hash;
+}
+
 val make_seeded_hash(val weak_keys, val weak_vals, val equal_based, val seed)
 {
   return do_make_hash(weak_keys, weak_vals,