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

[Eli Zaretskii <eliz@gnu.org>]

On September 1, 2020 11:31:14 AM GMT+03:00, "Gregory Heytings via Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org> wrote:
>
>>
>>> 26. therefore pcomplete-completions does not call pcomplete/cd but 
>>> eshell-complete-commands-list
>>
>> I guess this is the culprit
>>
>
>No, see below.
>
>>
>> and this is where the time is spent.
>>
>
>Yes, this is what I said.
>
>>
>> `eshell-complete-commands-list` eagerly builds the list of possible 
>> candidates and it takes a while whereas we should here return
>something 
>> quickly and cheaply, e.g. by returning a function which will build
>and 
>> return this list more lazily when completion is actually performed.
>>
>
>No, the bug is in the completion mechanism, not in eshell.  I don't
>know 
>exactly (because the mechanism is so complicated) where the completion 
>functions should be fixed, but it is clear that there is no reason to
>call 
>pcomplete-completions-at-point *three* times.

Would it help to profile the completion process in this use case using the built-in Lisp profiler?