How to write a compute-file producing utf8 output?

[Tomas Volf <~@wolfsden.cz>]

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Hello Guix,

I am currently struggling when trying to create a computed-file producing
internationalized content.  Simple reproducer is:

      (use-modules (gnu packages base)
                   (guix gexp))

      (computed-file
       "utf8-display"
       #~(with-output-to-file #$output
           (λ ()
             (display "猫\n"))))

This, when executed and printed, gives following result:

      /tmp $ guix build -e '(load "/tmp/yy.scm")'
      /gnu/store/fyr9h82v9hhbjm4f7lqsdnhs4c45sn3y-utf8-display
      /tmp $ cat /gnu/store/fyr9h82v9hhbjm4f7lqsdnhs4c45sn3y-utf8-display
      ?

As you can see, ? does not equal 猫.  I would expect the root cause to be the
same as #66777.

Any ideas what can I do about this?  Or, even better, why this does not just
work out of the box?

Thanks for your help,
Tomas

--
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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