destructuring-bind uses second value of initform as supplied-p value

[Steve Losh]

When using destructuring-bind with a &key parameter that has a supplied-p variable, if the keyword is not supplied and the initform returns multiple values, the second value will be used as the value of the supplied-p variable instead of NIL:

[SBCL] CL-USER> (destructuring-bind
                    (&key (x (values 1 2) x-supplied))
                    '()
                  (list x x-supplied))
; => (1 2)
; should be (1 NIL)

[SBCL] CL-USER> (lisp-implementation-version)
"2.0.1"

[SBCL] CL-USER> *features*
(:QUICKLISP :SB-BSD-SOCKETS-ADDRINFO :ASDF3.3 :ASDF3.2 :ASDF3.1 :ASDF3 :ASDF2 :ASDF :OS-UNIX
 :NON-BASE-CHARS-EXIST-P :ASDF-UNICODE :X86-64 :64-BIT :ANSI-CL :COMMON-LISP :ELF :GENCGC
 :IEEE-FLOATING-POINT :LINUX :LITTLE-ENDIAN :PACKAGE-LOCAL-NICKNAMES :SB-LDB :SB-PACKAGE-LOCKS
 :SB-THREAD :SB-UNICODE :SBCL :UNIX)

uname -a
Linux ouroboros 4.15.0-91-generic #92-Ubuntu SMP Fri Feb 28 11:09:48 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

[James Kalenius (aeshtaer)]

The source of the problem is pretty clear from the macroexpansion:

(destructuring-bind (&key (a (values :foo 'what) a?)) args
  (list args a a?))
=>
(SB-INT:BINDING* ((#:G486
                   (SB-C::CHECK-DS-LIST/&KEY ARGS 0 0 '(&KEY (A)) #(:A)))
                  (#:G487 (SB-C::DS-GETF #:G486 ':A))
                  ((A A?)
                   (IF (EQL #:G487 0)
                       (VALUES :FOO 'WHAT)
                       (VALUES (CAR (TRULY-THE CONS #:G487)) T))))
  (LIST ARGS A A?))

I think it can be fixed by wrapping another values call around the default value, i.e. in expand-ds-bind

(gen-test sense sup-p-form
          (if sup-p-var `(values ,val-form t) val-form)
          def)

should be

(gen-test sense sup-p-form
          (if sup-p-var `(values ,val-form t) val-form)
          `(values ,def nil))