seq_build: safeguard against adding to finished object.

* lib.c (seq_build_convert_to_finished): New function.
(seq_build_list_finish): call seq_build_convert_to_finished.
(sb_finished_ops): New static struct. All operations
except mark are null pointers so this will crash if
used.

1 files changed, 14 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index 9acb9abe..41f5db72 100644
--- a/lib.c
+++ b/lib.c
@@ -1502,6 +1502,8 @@ static void seq_build_list_pend(seq_build_t *bu, val item)
     seq_build_convert_to_improper(bu, item);
 }
 
+static void seq_build_convert_to_finished(seq_build_t *bu);
+
 static void seq_build_list_finish(seq_build_t *bu)
 {
   val obj = bu->obj;
@@ -1511,18 +1513,22 @@ static void seq_build_list_finish(seq_build_t *bu)
     us_rplacd(obj, nil);
     bu->obj = head;
   }
+
+  seq_build_convert_to_finished(bu);
 }
 
 static void seq_build_struct_finish(seq_build_t *bu)
 {
   seq_build_list_finish(bu);
   bu->obj = funcall1(bu->u.from_list_meth, bu->obj);
+  seq_build_convert_to_finished(bu);
 }
 
 static void seq_build_carray_finish(seq_build_t *bu)
 {
   seq_build_list_finish(bu);
   bu->obj = carray_list(bu->obj, bu->u.carray_type, nil);
+  seq_build_convert_to_finished(bu);
 }
 
 static void seq_build_improper_add(seq_build_t *bu, val item)
@@ -1586,6 +1592,9 @@ static struct seq_build_ops
                                        seq_build_improper_finish,
                                        seq_build_obj_mark);
 
+static struct seq_build_ops
+  sb_finished_ops = seq_build_ops_init(0, 0, 0, seq_build_obj_mark);
+
 static void seq_build_convert_to_list(seq_build_t *bu, val list)
 {
   if (list) {
@@ -1614,6 +1623,11 @@ static void seq_build_convert_to_improper(seq_build_t *bu, val atom)
   bu->ops = &sb_improper_ops;
 }
 
+static void seq_build_convert_to_finished(seq_build_t *bu)
+{
+  bu->ops = &sb_finished_ops;
+}
+
 void seq_build_init(val self, seq_build_t *bu, val likeobj)
 {
   bu->self = self;