From 57f2d25e19e1fee51508732beb46992e319e594c Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <campbell@mumble.net>
Date: Thu, 29 Nov 2018 02:11:51 +0000
Subject: [PATCH] Note local optional parameter bug.

---
 src/relnotes/bug-localoptparam | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 src/relnotes/bug-localoptparam

diff --git a/src/relnotes/bug-localoptparam b/src/relnotes/bug-localoptparam
new file mode 100644
index 000000000..803351c9f
--- /dev/null
+++ b/src/relnotes/bug-localoptparam
@@ -0,0 +1,13 @@
+Bug fix: LIAR previously miscompiled local procedures with optional
+parameters if they were never passed.
+
+Formerly MIT Scheme used unassigned reference traps for optional
+parameters without values; now it uses a #!default object.  But LIAR
+hadn't gotten the memo, and if every call site omitted the argument,
+LIAR would constant-fold an unassigned reference trap instead of
+#!default.
+
+(let ()
+  (define (test #!optional x)
+    (pp (map-reference-trap (lambda () x))))
+  (test))
-- 
2.25.1