bug#66114: [PATCH] Fix interactive prompt for selecting checkout directory

[Philip Kaludercic <philipk@posteo.net>]

Joseph Turner <joseph@breatheoutbreathe.in> writes:

> Philip Kaludercic <philipk@posteo.net> writes:
>
>> Joseph Turner <joseph@breatheoutbreathe.in> writes:
>>
>>> Tags: patch
>>>
>>> This patch fixes the interactive prompt in package-vc-checkout. See
>>> commit message for details.
>>>
>>> From 70061d76542968575555f247d4715d18ed3c4e75 Mon Sep 17 00:00:00 2001
>>> From: Joseph Turner <joseph@breatheoutbreathe.in>
>>> Date: Tue, 19 Sep 2023 23:58:43 -0700
>>> Subject: [PATCH] Fix interactive prompt for selecting checkout directory
>>>
>>> * lisp/emacs-lisp/package-vc.el (package-vc-checkout): Use
>>> read-directory-name instead of read-file-name with
>>> predicate.  Previously, it was impossible to interactively navigate to
>>> a nested subdirectory.
>>
>> I can "navigate" into whatever directory I want, but I don't get completion.
>
> You're right.
>
>>> ---
>>>  lisp/emacs-lisp/package-vc.el | 17 +++++++++++------
>>>  1 file changed, 11 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/lisp/emacs-lisp/package-vc.el b/lisp/emacs-lisp/package-vc.el
>>> index c7a30736e32..29b540d86b8 100644
>>> --- a/lisp/emacs-lisp/package-vc.el
>>> +++ b/lisp/emacs-lisp/package-vc.el
>>> @@ -823,12 +823,17 @@ repository.  If REV has the special value
>>>  `:last-release' (interactively, the prefix argument), that stands
>>>  for the last released version of the package."
>>>    (interactive
>>> -   (let* ((name (package-vc--read-package-name "Fetch package source: ")))
>>> -     (list (cadr (assoc name package-archive-contents #'string=))
>>> -           (read-file-name "Clone into new or empty directory: " nil nil t nil
>>> -                           (lambda (dir) (or (not (file-exists-p dir))
>>> -                                             (directory-empty-p dir))))
>>> -           (and current-prefix-arg :last-release))))
>>> +   (let* ((name (package-vc--read-package-name "Fetch package source: "))
>>> +          (desc (cadr (assoc name package-archive-contents #'string=)))
>>> +          (dir (read-directory-name "Clone into new or empty directory: ")))
>>> +     (unless (or (not (file-exists-p dir))
>>> +                 (directory-empty-p dir))
>>> +       (let ((subdir (expand-file-name (package-desc-full-name desc) dir)))
>>> +         (if (and (not (file-exists-p subdir))
>>> +                  (y-or-n-p (format "Create new directory %s ?" subdir)))
>>> +             (setf dir subdir)
>>
>> I'd prefer to use a setq here.
>>
>>> +           (user-error "Directory not empty: %S" (expand-file-name dir)))))
>>
>> This seems like an anti-feature to me, because you need to know what
>> directory is empty before confirming your choice, and if it is not
>> empty, you have to restart the entire command again.
>
> Yes, I agree.
>
> IIUC, we want to read from the user a directory which is either
> nonexistent or empty.  However, we also want the completions to include
> non-empty directories so that the user can easily select a deeply nested
> directory.  The current solution does not offer non-empty directories for
> completions, meaning that users must manually type in a potentially long
> path to a nested empty or nonexistent directory.

It is funny to me, that I probably never noticed this issue because I
have the habit of using hippie-expand to complete partial file names,
including in the minibuffer :)

> Here's a different idea I tried:
>
> (read-file-name "Clone into new or empty directory: " nil nil
>                 ;; Must match a nonexistent or empty directory
>                 (lambda (dir) (or (not (file-exists-p dir))
>                                   (directory-empty-p dir)))
>                 nil
>                 ;; `read-directory-name' accepts no PREDICATE
>                 ;; argument: hack `read-file-name' instead.
>                 (lambda (file-name) (file-directory-p file-name)))
>
> but this erroneously returns the default filename, which might be
> buffer-file-name or whatever string is currently in the minibuffer.

An issue I am observing, is that it allows selecting non-empty
directories.

> I would have expected that when MUSTMATCH is a function and it returns
> nil, a "[Match required]" message would appear.  

For the record, what completion system are you using.  I don't appear to
see this message at all.

>                                                  However, the behavior of
> read-file-name is unspecified when a MUSTMATCH function returns nil:
>
> - a function, which will be called with the input as the
>   argument.  If the function returns a non-nil value, the
>   minibuffer is exited with that argument as the value.
>
> Is this a bug, a case of under-documentation, or do I misunderstand something?
>
> I'm happy to post this in a separate bug thread if you think it's worth it.

Perhaps that would be worth doing, that way the people who know more
about completion than I do would be more likely to see it and help out.

>
> Joseph
>
>>> +     (list desc dir (and current-prefix-arg :last-release))))
>>>    (package-vc--archives-initialize)
>>>    (let ((pkg-spec (or (package-vc--desc->spec pkg-desc)
>>>                        (and-let* ((extras (package-desc-extras pkg-desc))

-- 
Philip Kaludercic