hash: fix broken copy_hash.

Impact assessment: this bug affects the correctness of
all programs which rely on copying hash tables. Direct
reliance means the use of copy-hash, or using the generic copy
function on hash objects.  Indirect reliance occurs through
hash-diff which uses copy-hash.  Nothing in TXR itself calls
hash-diff.  The the listener's Tab completion relies on
copy-hash for package-sensitive symbol visibility calculation.
Since that is an interactive feature, the impact is low.

* hash.c (copy_hash_chain): New static function.
(copy_hash): Use copy_hash_chain instead of copy_alist,
since the pairs are hash conses and not regular conses:
they have a hash value field that must be copied.

1 files changed, 15 insertions, 1 deletions

diff --git a/hash.c b/hash.c
index 8d3f2b37..444a32b8 100644
--- a/hash.c
+++ b/hash.c
@@ -677,6 +677,20 @@ val make_similar_hash(val existing)
   return hash;
 }
 
+static val copy_hash_chain(val chain)
+{
+  list_collect_decl(out, ptail);
+
+  for (; chain; chain = cdr(chain)) {
+    val entry = car(chain);
+    val nentry = cons(car(entry), cdr(entry));
+    nentry->ch.hash = entry->ch.hash;
+    ptail = list_collect(ptail, nentry);
+  }
+
+  return out;
+}
+
 val copy_hash(val existing)
 {
   struct hash *ex = coerce(struct hash *, cobj_handle(existing, hash_s));
@@ -698,7 +712,7 @@ val copy_hash(val existing)
   h->acons_new_c_fun = ex->acons_new_c_fun;
 
   for (iter = zero; lt(iter, mod); iter = plus(iter, one))
-    set(vecref_l(h->table, iter), copy_alist(vecref(ex->table, iter)));
+    set(vecref_l(h->table, iter), copy_hash_chain(vecref(ex->table, iter)));
 
   return hash;
 }