DEFSTRUCT :INCLUDE option does not accept symbols as slot descriptions

[Jan Moringen]

What I did:

  (defstruct bar (x 1))
  (defstruct (foo (:include bar x)))

What happens:
SBCL signals an error "The value X is not of type LIST".

What I expected to happen:
The structure class FOO should be defined with a slot X that has no initial value according to this passage in the specification entry for DEFSTRUCT:

  (:include included-structure-name {slot-description}*)
  Each slot-description must have a slot-name that is the same as that of some slot in the included
  structure. If a slot-description has no slot-initform, then in the new structure the slot has no initial value.

Note
The error is signaled in ENSURE-NON-STANDARD-CLASS which applies CAR to the slot descriptions in the :INCLUDE option.

SBCL version
2.3.6.debian

uname -a
Linux al 6.3.0-2-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.3.11-1 (2023-07-01) x86_64 GNU/Linux

*FEATURES*
(:BORDEAUX-THREADS :GLOBAL-VARS :THREAD-SUPPORT :CLOSER-MOP :SWANK
 ALEXANDRIA::SEQUENCE-EMPTYP :QUICKLISP :ASDF3.3 :ASDF3.2 :ASDF3.1 :ASDF3
 :ASDF2 :ASDF :OS-UNIX :NON-BASE-CHARS-EXIST-P :ASDF-UNICODE :ARENA-ALLOCATOR
 :X86-64 :GENCGC :64-BIT :ANSI-CL :COMMON-LISP :ELF :IEEE-FLOATING-POINT :LINUX
 :LITTLE-ENDIAN :PACKAGE-LOCAL-NICKNAMES :SB-CORE-COMPRESSION :SB-LDB
 :SB-PACKAGE-LOCKS :SB-THREAD :SB-UNICODE :SBCL :UNIX)