Re: What does `undecided' do for encoding text?

[Kenichi Handa <handa@m17n.org>]

In article <u63jisl2w.fsf@gnu.org>, Eli Zaretskii <eliz@gnu.org> writes:

> > I don't think so because it is just a fallback behavior, and
> > Elisp programmer should avoid specifying `undecided' on
> > encoding.

> This may have nothing to do with what the programmer did.  My use case
> was in Rmail: if the original message had non-ASCII text encoded with
> QP or B64, Rmail would (correctly) return `undecided' when it detects
> the message encoding.  Suppose you then edit the message and add
> non-ASCII characters as raw bytes, e.g. by base64-decode-region, and
> type "C-c C-c".  rmail-cease-edit now needs to encode the text and put
> it back into the mbox buffer, and the immediate choice it has for the
> pertinent coding-system is to use buffer-file-coding-system of the
> buffer where the message was edited.  But the value of
> buffer-file-coding-system in that buffer is `undecided'...

The situation is the same as visiting an ASCII only file,
entering some non-ASCII characters, and saving it.  In that
case, we use selecte-safe-coding-system to decide the coding
system to encode the buffer contents.  As I wrote before,
rmail-cease-edit should do the same or the similar thing.

> If you say that using `undecided' in encoding is ``considered
> harmful'', we should at least say that in the ELisp manual.  Although
> in the use case I described `undecided' did exactly what's right, and
> the only other correct choice is `raw-text'.

For a buffer that contains raw bytes, `raw-text' is the only
correct choice.

---
Kenichi Handa
handa@m17n.org