internal error externalizing recursive array

Was doing some fuzz testing and came up with this little monstrosity. If you stick it in a file and COMPILE-FILE it, it trips an internal type error during FASL dump.

(defparameter *death*
  '#.(let ((a1 #1=#2a((#1# #1#) (#1# #1#))))
       (make-array 2 :displaced-to a1)))

Expected behavior would of course be that it compiles fine, and the result loads as something similar.

This happens on SBCL 2.2.9.debian, as well as 2.3.9.33-1742bcc35 that I just built from git.

uname -a: Linux zeus 6.1.0-3-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.8-1 (2023-01-29) x86_64 GNU/Linux

*features*: (:ARENA-ALLOCATOR :X86-64 :GENCGC :64-BIT :ANSI-CL :COMMON-LISP :ELF :IEEE-FLOATING-POINT :LINUX :LITTLE-ENDIAN :PACKAGE-LOCAL-NICKNAMES :SB-LDB :SB-PACKAGE-LOCKS :SB-THREAD :SB-UNICODE :SBCL :UNIX)

Session with backtrace:

This is SBCL 2.3.9.33-1742bcc35, an implementation of ANSI Common Lisp.
More information about SBCL is available at <http://www.sbcl.org/>.

SBCL is free software, provided as is, with absolutely no warranty.
It is mostly in the public domain; some portions are provided under
BSD-style licenses. See the CREDITS and COPYING files in the
distribution for more information.
* (compile-file "/tmp/death.lisp")
; compiling file "/tmp/death.lisp" (written 02 OCT 2023 03:56:41 PM):

debugger invoked on a TYPE-ERROR @52AB53F3 in thread
#<THREAD tid=2291692 "main thread" RUNNING {1004490113}>:
  The value
    NIL
  is not of type
    (UNSIGNED-BYTE 32)
  when binding SB-C::VALUE

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT] Exit debugger, returning to top level.

(SB-C:WRITE-VAR-INTEGER NIL #()) [external]
0] backtrace

Backtrace for: #<SB-THREAD:THREAD tid=2291692 "main thread" RUNNING {1004490113}>
0: (SB-C:WRITE-VAR-INTEGER NIL #()) [external]
1: (SB-FASL::DUMP-VARINT NIL #<SB-FASL:FASL-OUTPUT "/tmp/death.fasl">)
2: (SB-FASL::DUMP-CIRCULARITIES (#S(SB-FASL::CIRCULARITY :TYPE :SVSET :OBJECT #(#1=#2A((#1# #1#) (#1# #1#)) #1#) :INDEX 1 :SLOT-NAME NIL :VALUE #1# :ENCLOSING-OBJECT #1#) #S(SB-FASL::CIRCULARITY :TYPE :SVSET :OBJECT #2=#(#1# #1# #1# #1#) :INDEX 3 :SLOT-NAME NIL :VALUE #1# :ENCLOSING-OBJECT #1#) #S(SB-FASL::CIRCULARITY :TYPE :SVSET :OBJECT #2# :INDEX 2 :SLOT-NAME NIL :VALUE #1# :ENCLOSING-OBJECT #1#) #S(SB-FASL::CIRCULARITY :TYPE :SVSET :OBJECT #2# :INDEX 1 :SLOT-NAME NIL :VALUE #1# :ENCLOSING-OBJECT #1#) #S(SB-FASL::CIRCULARITY :TYPE :SVSET :OBJECT #2# :INDEX 0 :SLOT-NAME NIL :VALUE #1# :ENCLOSING-OBJECT #1#)) #<SB-FASL:FASL-OUTPUT "/tmp/death.fasl">)
3: (SB-FASL:DUMP-OBJECT #(#1=#2A((#1# #1#) (#1# #1#)) #1#) #<SB-FASL:FASL-OUTPUT "/tmp/death.fasl">)
4: (SB-FASL::DUMP-CODE-OBJECT #<SB-C:COMPONENT :NAME "top level form" {1002858E23}> #<SB-ASSEM:SEGMENT {1002861D43}> 112 (#S(SB-C::FIXUP-NOTE :KIND :ABS32 :FIXUP #S(SB-C:FIXUP :NAME SB-IMPL::%DEFPARAMETER :FLAVOR :FDEFN-CALL :OFFSET 0) :POSITION 85)) NIL #<SB-FASL:FASL-OUTPUT "/tmp/death.fasl">)
5: (SB-FASL:FASL-DUMP-COMPONENT #<SB-C:COMPONENT :NAME "top level form" {1002858E23}> #<SB-ASSEM:SEGMENT {1002861D43}> 112 (#S(SB-C::FIXUP-NOTE :KIND :ABS32 :FIXUP #S(SB-C:FIXUP :NAME SB-IMPL::%DEFPARAMETER :FLAVOR :FDEFN-CALL :OFFSET 0) :POSITION 85)) NIL #<SB-FASL:FASL-OUTPUT "/tmp/death.fasl">)
6: (SB-C::%COMPILE-COMPONENT #<SB-C:COMPONENT :NAME "top level form" {1002858E23}>)
7: (SB-C::COMPILE-COMPONENT #<SB-C:COMPONENT :NAME "top level form" {1002858E23}>)
8: (SB-C::SUB-COMPILE-TOPLEVEL-LAMBDAS NIL T)
9: (SB-C::COMPILE-TOPLEVEL-LAMBDAS NIL T)
10: ((LAMBDA NIL :IN SB-C::SUB-COMPILE-FILE))
11: ((FLET SB-C::WITH-IT :IN SB-C::%WITH-COMPILATION-UNIT))
12: (SB-C::SUB-COMPILE-FILE #<SB-C::SOURCE-INFO {10027F7C43}> NIL)
13: (COMPILE-FILE "/tmp/death.lisp" :OUTPUT-FILE "" :VERBOSE NIL :PRINT NIL :EXTERNAL-FORMAT :DEFAULT :PROGRESS NIL :TRACE-FILE NIL :BLOCK-COMPILE NIL :ENTRY-POINTS NIL :EMIT-CFASL NIL)
14: (SB-INT:SIMPLE-EVAL-IN-LEXENV (COMPILE-FILE "/tmp/death.lisp") #<NULL-LEXENV>)
15: (EVAL (COMPILE-FILE "/tmp/death.lisp"))
16: (INTERACTIVE-EVAL (COMPILE-FILE "/tmp/death.lisp") :EVAL NIL)
17: (SB-IMPL::REPL-FUN NIL)
18: ((LAMBDA NIL :IN SB-IMPL::TOPLEVEL-REPL))
19: (SB-IMPL::%WITH-REBOUND-IO-SYNTAX #<FUNCTION (LAMBDA NIL :IN SB-IMPL::TOPLEVEL-REPL) {7F73ACCB7C1B}>)
20: (SB-IMPL::TOPLEVEL-REPL NIL)
21: (SB-IMPL::TOPLEVEL-INIT)
22: ((FLET SB-UNIX::BODY :IN SB-IMPL::START-LISP))
23: ((FLET "WITHOUT-INTERRUPTS-BODY-3" :IN SB-IMPL::START-LISP))
24: (SB-IMPL::%START-LISP)

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