Re: Order of eshell/pcomplete completions when cycling

[Tassilo Horn <tsdh@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> > I think you want string-collate-lessp, not string-lessp.  AFAIK,
>> > that's what the shells use.
>> 
>> Yes, you are right.  Unfortunately, it seems the function used for
>> `eshell-cmpl-compare-entry-function' (which is the default value for
>> `pcomplete-compare-entry-function' in eshell buffers) has no effect on
>> the order in which completions are cycled when hitting TAB repeatedly.
>
> Well, then maybe they should, at least as an option?

Yes, of course they should. :-)

I have no deep understanding of the emacs completion stuff.  But in
pcomplete.el there is

--8<---------------cut here---------------start------------->8---
(defun pcomplete--entries (&optional regexp predicate)
  "Like `pcomplete-entries' but without env-var handling."
  (let* ((ign-pred
[...snip...]
    (lambda (s p a)
      (if (and (eq a 'metadata) pcomplete-compare-entry-function)
          `(metadata (cycle-sort-function
                      . ,(lambda (comps)
                           (sort comps pcomplete-compare-entry-function)))
                     ,@(cdr (completion-file-name-table s p a)))
        (let ((completion-ignored-extensions nil)
              (completion-ignore-case pcomplete-ignore-case))
          (completion-table-with-predicate
           #'comint-completion-file-name-table pred 'strict s p a))))))
--8<---------------cut here---------------end--------------->8---

where the lambda returns a cycle-sort-function using
`pcomplete-compare-entry-function' if asked for completion metadata.
The docs say

,----[ (info "(elisp)Programmed Completion") ]
| ‘cycle-sort-function’
|      The value should be a function for sorting completions, when
|      ‘completion-cycle-threshold’ is non-‘nil’ and the user is cycling
|      through completion alternatives.  *Note (emacs)Completion
|      Options::.  Its argument list and return value are the same as for
|      ‘display-sort-function’.
`----

so that seems to be what I am looking for and eshell/pcomplete
initialize it correctly.

The returned lambda is only called via

   (complete-with-action action table newstring pred))

where table is that lambda.

I've verified that the lambda is never called with the a(ction) argument
bound to 'metadata, so the cycle-sort-function which would sort using
`pcomplete-compare-entry-function' is never asked for.

Grepping the sources, the only user of cycle-sort-function is
`completion-all-sorted-completions' which is never called by eshell or
pcomplete.  So the `pcomplete-compare-entry-function' will never every
be called.

I suspect that there has been a time where that used to work, and in the
meantime the completion stuff has changed and forgotten that some
completion users want sorted completions also without calling
`completion-all-sorted-completions'.

Bye,
Tassilo