Re: Saving Erc buffers (Or: Broken C-x C-w)

[Alcor]

"J.P." <jp@neverwas.me> writes:

> Alcor <alcor@tilde.club> writes:
>
>> Hi all,
>>
>> I'm not sure if this is a bug, but I'll ask just to make sure: I'd like
>> to save an Erc (channel) buffer to a file. Intuitively, the Emacsism for
>> this would be C-x C-w or `write-file'.
>>
>> However, this does not work on Erc. Or rather, it _does_ save the buffer
>> to a file, at the rather steep price of breaking the Erc server
>> state. It looks like Erc's part hook isn't executed, and there seems to
>> be no simple way to repair the Erc session afterwards (except via
>> quitting and /reconnect'ing).
>
> One consequence of the PART hook not running is that items in the
> `erc-server-users' table retain stale references to the saved buffer,
> which is no longer an ERC buffer. Aside from that, it seems the saved
> buffer's `local-minor-modes' value retains ERC-specific minor modes and
> its `kill-buffer-hook' is still set to `erc-kill-buffer-function'.

There are also a myriad of other visual issues, e.g. fill/wrapping
breaking, timestamps disappearing, and some of the faces/formatting
changing.

>> So the question is - what's the Erc-approved way for doing a one-off
>> write out of a channel buffer to a file? (as opposed to logging).
>>
>> And, if possible, is there a way to fix the behavior of C-x C-w in Erc?
>
> Perhaps we ought to ask ourselves what we want to happen when running
> this command and how that compares to what happens when doing so in
> other non-file-based modes, like `gud-mode' or various REPLs.

I tried testing on a few other REPLs/shells:

* Eshell: Writes the file out & sets its visited file to the given
  filename. Otherwise, the shell remains functional.
* ansi-term: Likewise.

No adverse effects are observed otherwise and both shells remain
usable. Hitting C-x C-s writes out the current buffer content as expected.

> If the answer turns out to be that C-x C-w (or C-x C-s) should act like
> C-x h M-x write-region RET, then we should maybe consider declaring
> `erc-mode' as `special', something that's been brought up casually on
> occasion but never proposed in earnest (AFAIK).
>
> As far as implementations go, we likely couldn't have `erc-mode' inherit
> from `special-mode' because `readonly' is a module and thus optional.
> So, we'd most likely have to do a
>
>   (put 'erc-mode 'mode-class 'special)
>
> in ERC's major-mode definition.

I tried out (put 'erc-mode 'mode-class 'special) and was surprised to
see that it (mostly) seems to work. With that active, the Erc buffer
remains functional on C-x C-w. However, the buffer is renamed to the
filename, which is even reflected in the bufbar. I'm not sure whether
the latter behavior can be suppressed, but if possible, then this would
seem like a fair solution (although some other way of indicating that
the Erc buffer is bound to a file will still be needed).

(Note: I tested this on a server buffer for like ~2 minutes, so there
might be adverse effects I'm unaware of, but it *looks* definitely less
broken)

In the end, I remain unsure of the best way to handle this. Inheriting
from 'special seems like a step in the right direction and warrants some
further investigation. In the meantime, C-x h M-x write-region RET is
also acceptable.

Cheers,
-A.