Re: why is my cd command on eshell on Windows so slow?

[Wayne Harris via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>]

Wayne Harris via Users list for the GNU Emacs text editor
<help-gnu-emacs@gnu.org> writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>>>>> %cd dir/
>>>>> 0.001 secs
>>>>> %
>> [...]
>>> It appears that the delay has nothing to do with Windows or with the
>>> cd-command.  It seems to be the procedure
>>>
>>>   completion-in-region--postch
>>
>> Sounds like bug#41423.
>> If that's the case, then I suggest you try the code in Emacs's `master`
>> where it should be fixed.
>
> It really sounds like bug#41423, even because the workaround provided by
> Gregory Heytings solves the problem, that is, I don't notice any slow
> down after applying:
>
> (add-hook
>  'eshell-mode-hook
>  (function (lambda ()
>              (setq completion-at-point-functions '(pcomplete t)))))
>
> On the other hand, applying your patch...
>
> diff --git a/lisp/eshell/em-cmpl.el b/lisp/eshell/em-cmpl.el
> index faf749d836..744be525ec 100644
> --- a/lisp/eshell/em-cmpl.el
> +++ b/lisp/eshell/em-cmpl.el
> @@ -399,16 +399,21 @@
>  
>  (defun eshell-complete-commands-list ()
>    "Generate list of applicable, visible commands."
> -  (let ((filename (pcomplete-arg)) glob-name)
> +  ;; Building the commands list can take quite a while, especially over Tramp
> +  ;; (bug#41423), so do it lazily.
> +  (let ((glob-name
> +	 ;; When a command is specified using `eshell-explicit-command-char',
> +         ;; that char is not part of the command and hence not part of what
> +         ;; we complete.  Adjust `pcomplete-stub' accordingly!
> +	 (if (and (> (length pcomplete-stub) 0)
> +	          (eq (aref pcomplete-stub 0) eshell-explicit-command-char))
> +	     (setq pcomplete-stub (substring pcomplete-stub 1)))))
> +    (completion-table-dynamic
> +     (lambda (filename)
>      (if (file-name-directory filename)
>          (if eshell-force-execution
>              (pcomplete-dirs-or-entries nil #'file-readable-p)
>            (pcomplete-executables))
> -      (if (and (> (length filename) 0)
> -	       (eq (aref filename 0) eshell-explicit-command-char))
> -	  (setq filename (substring filename 1)
> -		pcomplete-stub filename
> -		glob-name t))
>        (let* ((paths (eshell-get-path))
>  	     (cwd (file-name-as-directory
>  		   (expand-file-name default-directory)))
> @@ -455,7 +460,7 @@
>  			    (and eshell-show-lisp-alternatives
>  				 (null completions)))
>  			(all-completions filename obarray #'functionp))
> -		   completions)))))))
> +		      completions)))))))))
>  
>  (define-obsolete-function-alias 'eshell-pcomplete #'completion-at-point "27.1")
>
> ...does not make any noticeable change.

[...]

Sorry!  It does make a noticeable change.  Your patch seems to solve the
problem quite well for me.  I believe this is case closed.  Thank you
for the marvelous patch.