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.

6 files changed, 34 insertions, 7 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));
 }
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,
diff --git a/hash.h b/hash.h
index 8792b609..3b773a6b 100644
--- a/hash.h
+++ b/hash.h
@@ -39,6 +39,7 @@ extern struct cobj_class *hash_cls;
 
 ucnum equal_hash(val obj, int *count, ucnum);
 val make_seeded_hash(val weak_keys, val weak_vals, val equal_based, val seed);
+val tweak_hash(val hash, val weak_keys, val weak_vals);
 val make_hash(val weak_keys, val weak_vals, val equal_based);
 val make_eq_hash(val weak_keys, val weak_vals);
 val make_similar_hash(val existing);
diff --git a/lib.c b/lib.c
index 0e8bbbb1..274d3956 100644
--- a/lib.c
+++ b/lib.c
@@ -14052,6 +14052,7 @@ int compat_fixup(int compat_ver)
 
   eval_compat_fixup(compat_ver);
   rand_compat_fixup(compat_ver);
+  parse_compat_fixup(compat_ver);
   return 0;
 }
 
diff --git a/parser.c b/parser.c
index 0deb3867..169b58b0 100644
--- a/parser.c
+++ b/parser.c
@@ -1878,7 +1878,7 @@ void parse_init(void)
   parser_cls = cobj_register(parser_s);
 
   protect(&stream_parser_hash, &unique_s, &catch_all, convert(val *, 0));
-  stream_parser_hash = make_hash(t, nil, nil);
+  stream_parser_hash = make_hash(t, t, nil);
   catch_all = cons(t, nil);
 
   parser_l_init();
@@ -1897,3 +1897,9 @@ void parse_init(void)
   reg_fun(intern(lit("repl"), system_package), func_n4(repl));
   reg_mac(json_s, func_n2(me_json));
 }
+
+void parse_compat_fixup(int compat_ver)
+{
+  if (compat_ver <= 266)
+    tweak_hash(stream_parser_hash, t, nil);
+}
diff --git a/parser.h b/parser.h
index 3d682daa..b504b083 100644
--- a/parser.h
+++ b/parser.h
@@ -148,3 +148,4 @@ val parser_set_lineno(val self, val stream, val lineno);
 val parser_errors(val parser);
 val parse_errors(val stream);
 void parse_init(void);
+void parse_compat_fixup(int compat_ver);