Subject: bug#56751: Protocol of parent record type is ignored

From: Maxime Devos <[email-masked]>
Date: Sun, 24 Jul 2022 22:56:58 +0200

(import (rnrs records syntactic)
         (rnrs base))

(define-record-type
     (#{I have one field, but no need to set it, I'll do it myself}# 
make-1 type-1?)
   (fields (immutable #{field with a fixed value}# #{get first field 
value}#))
   (protocol
    (lambda (%make)
      (lambda ()
        (#;(%make) ;; XXX unlike what is documented, this needs to be:
     %make
     ;; instead.  Bug in inmplementation or documentation?  Not the issue
     ;; I wanted to note though.
     "some value")))))

(assert (string=? (#{get first field value}# (make-1)) "some value")) ; ok

(define-record-type (#{the subtype}# make-2 type-2?)
   (parent #{I have one field, but no need to set it, I'll do it myself}#))

;;  The problem:
;;
;; Guile seems to have forgotten that the protocol of the supertype,
;; and hence asks for a value for the argument even though the protocol
;; of the original record type normally would give it a value.
;; (Ok, this is interpretation for the symptoms, I haven't yet tested 
this against
;; the source code).
;;
;; This manifests as make-2 havng arity 1 though it should have arity 1:
#;
(assert (equal? (#{get first field value}# (make-2) "some value"))) ;; 
--> wrong number of arguments to #<procedure ...>

;; We can due to the bug also break the abstraction: (see assert failure)
(assert (equal? (#{get first field value}# (make-2 
'break-the-abstraction)) "some value")) ;; --> wrong number of arguments 
to #<procedure ...>

;; Note: if I explicitly write the protocol for the subtype, then all 
the problems disappear
;; (work-around).  For an example in the wild, see the supertype 
<lost-and-found> at
;; 
<https://git.gnunet.org/gnunet-scheme.git/tree/gnu/gnunet/concurrency/lost-and-found.scm>
;; and the subtype at 
<https://git.gnunet.org/gnunet-scheme.git/tree/gnu/gnunet/dht/client.scm#n583>
;; (Not the best example, as I give the new fields default values as 
well, but you get the idea.)