From f7c25c5777ea349396f1ba71739bf3eccd623f70 Mon Sep 17 00:00:00 2001
From: dg1sbg <frank.goenninger@goenninger.net>
Date: Mon, 3 Aug 2026 23:22:20 +0200
Subject: [PATCH] Do not raise from cmpltv's print-object on a half-built
 creator

print-object for vcreator guards %prototype with slot-boundp but reads
(index object) unguarded, and the creator method reads it unguarded
too.  A creator whose index has not been assigned therefore signals an
unbound-slot error from inside the printer, which replaces whatever
condition was actually being reported and splices the new message into
the middle of the old one:

  #<CMPLTV::BASE-STRING-CREATOR [no prototype]The slot CMPLTV::%INDEX
    is unbound in an instance of CMPLTV::BASE-STRING-CREATOR.

Guard both reads the way %prototype already is.

Also widen the %index slot type to (or null (integer 0)), matching
Maclina.  The slot's initform is nil, which the declared (integer 0)
excludes; nothing enforces it today, but the declaration contradicts
the initform.
---
 src/lisp/kernel/cmp/cmpltv.lisp | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/lisp/kernel/cmp/cmpltv.lisp b/src/lisp/kernel/cmp/cmpltv.lisp
index 744ecfc94e..287173b9bf 100644
--- a/src/lisp/kernel/cmp/cmpltv.lisp
+++ b/src/lisp/kernel/cmp/cmpltv.lisp
@@ -38,7 +38,7 @@
 ;;; The object may be fully initialized or may require further initialization.
 (defclass creator (instruction)
   ((%index :initform nil :initarg :index :accessor index
-           :type (integer 0))))
+           :type (or null (integer 0)))))
 ;;; A creator for which a prototype value (which the eventual LTV will be
 ;;; similar to) is available.
 (defclass vcreator (creator)
@@ -55,7 +55,9 @@
 
 (defmethod print-object ((object creator) stream)
   (print-unreadable-object (object stream :type t)
-    (format stream "~d" (index object)))
+    (if (slot-boundp object '%index)
+        (format stream "~d" (index object))
+        (write-string "[no index]" stream)))
   object)
 
 (defmethod print-object ((object vcreator) stream)
@@ -63,7 +65,9 @@
     (if (slot-boundp object '%prototype)
         (prin1 (prototype object) stream)
         (write-string "[no prototype]" stream))
-    (format stream " ~d" (index object)))
+    (if (slot-boundp object '%index)
+        (format stream " ~d" (index object))
+        (write-string " [no index]" stream)))
   object)
 
 ;;; An instruction that performs some action for effect. This can include