bug#39634: All keyowrds hash to the same value

[Andy Wingo <wingo@igalia.com>]

On Thu 20 Feb 2020 17:19, Ludovic Courtès <ludo@gnu.org> writes:

> Of all the scm_tc7_ values listed in ‘scm.h’, the following are not
> explicitly listed (so they go to the default case that hashes the first
> word):

Reformatting your list so I can check one by one :)

>   variable,
>   hashtable,
>   fluid,
>   dynamic_state,
>   frame,
>   atomic_box,
>   program,
>   vm_cont,
>   weak_set,
>   weak_table,
>   port

No equal? implementation, so should hashq() instead.

>   bytevector,
>   array,
>   bitvector,

These have equal? implementations, and what's more, a bitvector can
equal? an array... I think we have another bug!

  ;; Project 2d array as 1d array (scm_tc7_array)
  (define x
    (make-shared-array #2b((#t #t #t)) (lambda (i) (list 0 i)) '(0 2)))
  ;; scm_tc7_bitvector
  (define y #*111)

  (equal? x y) ;; => #t
  (equal? (hash x #xffffffff) (hash y #xffffffff)) ;; => #f
            
Similarly for 1-d scm_tc7_array versus regular vectors, bytevectors,
etc.

Fixing this will not be straightforward...  I think basically 1d arrays
need some special hashing logic so that e.g. vectors and 1d arrays hash
to the same thing.

>   stringbuf,
>   values,

These are never exposed to Scheme, and never compared using equal?
AFAIU.  No need for special cases.

Basically I think the tc7 case should default to hashq, and include
special cases for the ones that have equal? implementations or which
have read syntax.

Sound right to you?

Andy