bug#62029: 29.0.60; Allow users to customize eldoc buffer separator

[Dmitry Gutov <dmitry@gutov.dev>]

On 12/04/2023 14:06, João Távora wrote:
>>> elisp-mode.el.  Do you have something to say about that?  Did you try
>>> the patch I showed Yuan?
>> I have applied it. What should I be looking at?
> Right. That's a good sign it itself.  Here, have some more patch:
> 
>    (setq-default eldoc-documentation-strategy 'eldoc-documentation-compose)
>    (add-hook 'emacs-lisp-mode-hook
>      (lambda () (setq-local eldoc-echo-area-use-multiline-p 1)))
> 
> Then go on with elisp your life and maybe peek into M-x eldoc-doc-buffer
> once in a while.

What is the reason to have a special value for Elisp again?

One obvious downside is that if the user customizes it to some different 
value (e.g. 2, limiting the height of the window below), it won't be 
honored by Elisp without some extra work on the part of the user. So if 
we want to do that, we'd need some strong argument for why Elisp is 
different from everyone else.

And the thing with window jumping/blinking seems common enough across 
the modes. It's easiest to reproduce when just using Eglot with Company 
(for some reason or other, the blinking seems absent without the latter; 
but I only tested one simple scenario in one configuration).

But in Elisp -- even if I just move the cursor with arrows or C-f/C-b, 1 
times out of 2 the echo are window will blink.

It's trivially reproduced even with 'emacs -Q': just add somewhere 
inside an Elisp buffer:

   (remove-hook asd)

when flymake-mode is enabled and eldoc-documentation-strategy is 
'eldoc-documentation-compose, and eldoc-echo-area-use-multiline-p is not 
1, and move around 'asd' with C-f and C-b.

Is that bug Elisp-specific? That would seem odd.