bug#27270: display-raw-bytes-as-hex generates ambiguous output for Emacs strings

[Lars Ingebrigtsen <larsi@gnus.org>]

Paul Eggert <eggert@cs.ucla.edu> writes:

> Not surprising, since most people don't set
> display-raw-bytes-as-hex. But that doesn't mean it's not a
> problem. Quoting bugs can be issues even if they're unlikely to occur
> at random. (Think SQL injection. :-)

I don't think we're talking quite the same magnitude -- this is a
problem if you're cutting strings from a -nw Emacs and pasting into a
different Emacs and then using the Lisp reader to read it back.  And
then there's a raw byte in the string.

The likelihood of anybody actually encountering this issue is ... small.

>> I tend to think that introducing a new syntax just to fix it
>> isn't worth it.
>
> That's fine, so let's fix the problem as originally suggested. That
> is, display the string returned by (format "%c%c" #x9e #x66) as
> "\x9e\x66" (equivalent to (concat "\x9e" "\x66") which is correct)
> instead of as "\x9ef" (equivalent to "\N{BENGALI DIGIT NINE}" which is
> wrong).
>
> This fixes the problem and doesn't introduce new syntax.

You want to quote all %c as if they were raw bytes?  Or only following a
raw byte?  And what about

(format "%cf" #x9e)

which was the originally reported issue?

In any case, this would definitely be a regression, because it creates
very confusing displayed strings.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no