bug#41423: 27.0.91; eshell file completion in tramp dir is slow (3 minutes) [regression on pretest]

[Drew Adams]

>> What is still missing IMO is a general description/documentation of
>> the various parts of the completion mechanisms (completion-at-point,
>> completion-in-region, pcomplete, pcomplete-completion-at-point,
>> comint-completion-at-point, icomplete, ...) in Emacs behave and
>> interact. I was completely lost when I started working on this bug,
>> things are a bit clearer now, but still not very clear.
> 
> +1
> 
> Exactly this is the reason I've tried and failed to work on completion
> problems. Several times.

+1

And it's not just a lack of doc, I think.
The completion mechanism (e.g. minibuffer.el) is a labyrinth.