bug#31376: 26.0.50; print-charset-text-property not honored

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Cc: handa@gnu.org,  31376@debbugs.gnu.org,  schwab@linux-m68k.org,  
> eller.helmut@gmail.com
> Date: Sun, 13 May 2018 15:42:02 -0400
> 
> > We could mention this exception in the manual.
> 
> Yeah, I think we should.  Here's a new patch with updated manual and
> tests.

Thanks.

One minor comment about the tests:

> +(defun print-tests--prints-with-charset-p (ch odd-charset)
> +  "Return t if `prin1-to-string' prints CH with the `charset' property.
> +CH is propertized with a `charset' value according to
> +ODD-CHARSET: if nil, then use the one returned by `char-charset',
> +otherwise, use a different charset."
> +  (integerp
> +   (string-match
> +    "charset"
> +    (prin1-to-string
> +     (propertize (string ch)
> +                 'charset
> +                 (if odd-charset
> +                     (car (if (eq (char-charset ch) (car charset-list))
> +                              charset-list
> +                            (cdr charset-list)))
> +                   (char-charset ch)))))))

This seems to rely on some relationship between what char-charset
returns and the car of charset-list, is that right?  AFAIK, when
ODD-CHARSET is non-nil, you want to propertize with a charset that is
_different_ from what char-charset returns, but taking the first or
the second member of charset-list doesn't guarantee that.  It could
work with the particular characters you used for the tests, but if
this function is limited to such characters, we should document that
in the doc string or comments, lest someone will try to expand the
tests and will see strange failures.

Thanks, I have no other comments.