Re: highlight-indent-guides in display engine

[Ergus <spacibba@aol.com>]

On Fri, Jul 12, 2019 at 11:58:43AM +0200, Ergus wrote:
>On Fri, Jul 12, 2019 at 09:57:24AM +0300, Eli Zaretskii wrote:
>>>Date: Fri, 12 Jul 2019 02:21:27 +0200
>>>From: Ergus <spacibba@aol.com>
>>>Cc: emacs-devel@gnu.org
>>>
>>>>I don't think I understand: what do you mean by "add the indicator"?
>>>>How would this indicator look like?
>>>>
>>>Maybe a vertical bar (like our previous column indicator) or a width
>>>line. Or something customizable somehow. We just need to look around,
>>>there are several alternatives. We must chose the one that fits better
>>>and produces less complications for us. But provides the functionality
>>>somehow.
>>>
>>>I don't thing how the indicator looks like may be a problem, but how
>>>accurate or specific it behaves.
>>>
>>>I am just looking around and Geany adds some vertical points as the
>>>indicator positions (every tab or every x spaces). But the spaces are
>>>only "indicated" when used for the indentation..
>>>
>>>Sublime behaves in the same way. But there is an option to highlight the
>>>indicator only in the blocks around the current cursor. (As in the
>>>attachement)
>>
>>I didn't receive any attachments with your message.
>>
>>>Athom on the other hand seems to behave as in the
>>>highlight-indent-guides.el package:
>>>https://atom.io/packages/indent-guide-improved
>>>
>>>With the animations and so on. Which seems to be the most complete
>>>behavior, but less efficient.
>>
>>The animations and highlighting inside the current block should be in
>>Lisp, not in the display code.  If at all.
>>
>>>In all the cases I just see that they add the indicator based on the
>>>characters between the beginning of the line and the indentation (first
>>>non blank character) not looking at the previous lines. They ignore if
>>>there is a previous line  with wrong indentation or if the current line
>>>adds 3 tabs more respecting to the previous one.
>>>
>>>So, implementing it in this way doesn't seems to be so complex right?
>>
>>So basically you are talking about displaying some special glyph at
>>every tab stop inside leading whitespace of a line, or making each
>>tab-stop width have a different background color?  Yes, this should be
>>possible to do in the display code.  I just hope enough people will
>>see this as sufficient, because if most current users of these
>>packages won't switch, this new feature will not be worth its
>>development, documentation, and maintenance effort.  Maybe we should
>>ask on Reddit first?
>
>Hi Eli:
>
>I think several people will prefer to have the whole functionalities and
>options to customize (as usual in emacs if there is a feature that
>solves N issues, then somebody will come asking for the N+1 option.)
>
>But in any case the minimal solution will be enough for a big number of
>users if it compensates with performance.
>
>But I agree that we must ask in reddit. May you please add a reddit
>poster about?  Because as I don't use reddit very often, most users
>ignore them.
>
>Thanks in advance,
>Ergus
>

BTW:

Thinking more about this, there is an important corner case with my
simplistic solution: Lisp.

While the simplest solution will work in most of the cases: the
more popular languages (C, C++, Java, PHP, Python, Rust, Ruby,
JavaScript), and others no so popular (Fortran, Lua, Assembler, Bash,
Go) because their indentation is very regular; the lisp indentation is
very different and irregular (As Emacs indents it, I don't know the
rules it follows).

So, the simplistic solution won't work at all for the Lisp (common-lisp,
Scheme, Elisp) family and may be even a nuisance when writing Lisp :(. I
don't find any other language family with the same issue, but probably
there are other examples

Any idea here?
At least for the lisp case?