Re: decode-coding-string gone awry?

[David Kastrup <dak@gnu.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> instead of being processed directly from the process filter, then
>>> you should also ensure that this buffer is unibyte.
>
>> Yuk.  The problem is that this buffer is not only processed by
>> preview-latex, but also by AUCTeX, and the versions that get combined
>> may be different.  AUCTeX uses the source code buffer's file encoding
>> by default, which is fine for basically unibyte based coding systems.
>
> If you can't change this part, then your best bet might be to do something
> like:
>
> (defun preview-error-quote (string)
>   "Turn STRING with potential ^^ sequences into a regexp.
> To preserve sanity, additional ^ prefixes are matched literally,
> so the character represented by ^^^ preceding extended characters
> will not get matched, usually."
>   (let (output case-fold-search)
>     (while (string-match "\\^*\\(\\^\\^\\(\\([@-_?]\\)\\|[8-9a-f][0-9a-f]\\)\\)+"
>                          string)
>       (setq output
>             (concat output
>                     (regexp-quote (substring string 0 (match-beginning 1)))
>                     (decode-coding-string
>                      (preview-dequote-thingies (substring (match-beginning 1)
>                                                           (match-end 0)))
>                      buffer-file-coding-system))
>             string (substring string (match-end 0))))
>     (setq output (concat output (regexp-quote string)))
>     output)))
>
> BTW, you can use the 3rd arg to string-match to avoid consing strings for
> `string'.
>
> This way you only apply decode-coding-string to the part of the
> string which is still undecoded but not to the rest.

No use.  The gag precisely is that TeX may decide to split a _single_
Unicode character into some bytes that it will let go through
unchanged, and some bytes that it will transcribe into ^^ba notation.
If decode-coding-string is supposed to have a chance of reassembling
this junk, it must only be run at the end of reconstructing the byte
stream.  Yes, this is completely insane.  No, I can't avoid having to
deal with it somehow.

Give me a clue: what happens if a process inserts stuff with 'raw-text
encoding into a multibyte buffer?  'raw-text is a reconstructible
encoding, isn't it, so the stuff will get converted into some prefix
byte indicating "isolated single-byte entity instead of utf-8 char"
and the byte itself or something, right?  And decode-encoding-string
does not want to work on something like that?

I have to admit to total cluelessness.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum