bug#37189: 25.4.1: vc-hg-ignore implementation is missing

[Eli Zaretskii <eliz@gnu.org>]

> From: Wolfgang Scherer <Wolfgang.Scherer@gmx.de>
> Date: Sat, 1 Feb 2020 02:20:08 +0100
> 
> I don't think, that the problem with ignore specs can be solved in
> this (adhoc) manner. It should (finally) be properly designed.
> 
> There is a fundamental difference between per-directory ignore specs
> and per-tree ignore specs. Let me try to outline, where I see the
> problem with the current implementation:
> 
> 1. Per-tree VC support is (unecessarily) mapped onto per-directory
>    semantics.
> 2. `vc-ignore` is a quick and dirty afterthought, which does not
>    properly model per-tree use cases.
> 3. The rationale for my implementation of `vc-hg-ignore` covers
>    several use cases, which should be considered for a proper design.

Could you please elaborate on these 3 points?  I've read the rest of
your message at least twice, and I still don't think I understand your
POV on these 3 issues well enough to make up my mind about them.  I
appreciate the overview of the history of these features -- it might
very well help us understand your POV -- but the POV itself is not
clearly presented, AFAICT, so I at least couldn't find a path from the
history of these features to the problems you allude to.  And the
history alone cannot explain the problems in the current design,
because there's nothing wrong in evolving a design per se.

IOW, I'm OK with discussing design issues of ignoring files in VC, but
please let's begin by presenting clear and detailed descriptions of
the problems in the current design, and why you think the current
design cannot easily support valid use cases with modern VCSes.

Thanks.