Re: ielm automatic saving of history -- bug 67000

[Madhu]

*  Eli Zaretskii <eliz@gnu.org> <864j5dsgot.fsf@gnu.org>
Wrote on Tue, 15 Oct 2024 15:18:10 +0300
>> Date: Tue, 15 Oct 2024 10:16:33 +0530 (IST)
>> From: Madhu <enometh@meer.net>
[re:  savehist for ielm history]

>> I think that part is covered. if you see the top of ~/.emacs.d/history
>> the coding system is specified, the savehist-coding-system mechanism
>> takes care of this to you.  But I haven't tried this idea out yet (to
>> see the interactions with comint).
>
> The problem, AFAIU, is not the specification of the encoding when the
> file is written, the problem is to select the right encoding to begin
> with.  utf-8-emacs-unix is how characters are represented in Emacs
> internally, so it by definition can encode any character in the
> history; this is not true for any other encoding.  I believe this
> issue was what prevented you from existing Emacs, the issue you
> described in your original post.  Apologies if I misunderstood.


The point I wanted to make was that savehist-save binds
coding-system-for-write (to 'utf-8-unix) and this seems to work
without throwing a "coding system error".

my ~/.ielm-history (which gets read into comint-input-ring) has this
line (but with raw characters)

```
(rfc2047-encode-string "foo \303\200 bar")
```

(funcall ielm--exit) in the ielm buffer causes the coding system warning:

"These default coding systems were tried to encode the
following[...].. utf-8-unix"

However

```
(let ((coding-system-for-write 'utf-8-unix)) (funcall ielm--exit))
```

saves the history according to the code in ielm--exit without the
coding system error.

but coding-system-for-write is still 'utf-8-unix and not
'utf-8-emacs-unix so I think I still need an explanation, please.

(Also I think I forgot to mention the code in ielm-mode presently sets
kill-buffer-hook to a function rather than adding the function to the
hook variable)