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, 15 insertions, 6 deletions

diff --git a/eval.c b/eval.c
index d51eb5d3..6ed4a7d1 100644
--- a/eval.c
+++ b/eval.c
@@ -6488,12 +6488,12 @@ void eval_init(void)
           &call_f, &iter_begin_f, &iter_from_binding_f, &iter_more_f,
           &iter_item_f, &iter_step_f,
           &unbound_s, &origin_hash, &const_foldable_hash, convert(val *, 0));
-  top_fb = make_hash(t, nil, nil);
-  top_vb = make_hash(t, nil, nil);
-  top_mb = make_hash(t, nil, nil);
-  top_smb = make_hash(t, nil, nil);
-  special = make_hash(t, nil, nil);
-  builtin = make_hash(t, nil, nil);
+  top_fb = make_hash(t, t, nil);
+  top_vb = make_hash(t, t, nil);
+  top_mb = make_hash(t, t, nil);
+  top_smb = make_hash(t, t, nil);
+  special = make_hash(t, t, nil);
+  builtin = make_hash(t, t, nil);
   op_table = make_hash(nil, nil, nil);
   pm_table = make_hash(nil, nil, nil);
 
@@ -7342,6 +7342,15 @@ void eval_init(void)
 
 void eval_compat_fixup(int compat_ver)
 {
+  if (compat_ver <= 266) {
+    tweak_hash(top_fb, t, nil);
+    tweak_hash(top_vb, t, nil);
+    tweak_hash(top_mb, t, nil);
+    tweak_hash(top_smb, t, nil);
+    tweak_hash(special, t, nil);
+    tweak_hash(builtin, t, nil);
+  }
+
   if (compat_ver <= 107)
     reg_fun(intern(lit("flip"), user_package), func_n1(swap_12_21));
 }