bug#62700: 29.0.60; minibuffer-{previous,next,choose}-completion behave unintuitively when point is not at end of buffer

[sbaugh]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: sbaugh@catern.com
>> Date: Fri, 21 Apr 2023 18:56:35 +0000 (UTC)
>> Cc: Spencer Baugh <sbaugh@janestreet.com>, 62700@debbugs.gnu.org,
>>      juri@linkov.net
>> 
>> >> Ah, I thought Eli still wanted a backport version because this changes
>> >> code which has been on Emacs 29 for over a year.
>> >
>> > Indeed, that's what I would like to see on the release branch.  Mainly
>> > because even if this is deemed a bug, it happens in a relatively rare
>> > situation, so I'd like to avoid risking breakage in code which affects
>> > other situations.
>> 
>> Here's the backport for the release branch.
>
> Thanks, but I'd like to make this still safer for the release branch:
>
>> --- a/lisp/minibuffer.el
>> +++ b/lisp/minibuffer.el
>> @@ -4464,13 +4464,21 @@ minibuffer-next-completion
>>  When `minibuffer-completion-auto-choose' is non-nil, then also
>>  insert the selected completion to the minibuffer."
>>    (interactive "p")
>> -  (let ((auto-choose minibuffer-completion-auto-choose))
>> +  (let* ((auto-choose minibuffer-completion-auto-choose)
>> +         ;; Backported fix for bug#62700
>> +         (md (completion--field-metadata 
>> (minibuffer--completion-prompt-end)))
>> +         (base-suffix
>> +          (if (eq (alist-get 'category (cdr md)) 'file)
>> +              (buffer-substring (save-excursion (search-forward "/" nil t) 
>> (point))
>> +                                (point-max))
>> +            "")))
>>      (with-minibuffer-completions-window
>>        (when completions-highlight-face
>>          (setq-local cursor-face-highlight-nonselected-window t))
>>        (next-completion (or n 1))
>>        (when auto-choose
>> -        (let ((completion-use-base-affixes t))
>> +        (let ((completion-use-base-affixes t)
>> +              (completion-base-affixes (list (car completion-base-affixes) 
>> base-suffix)))
>>            (choose-completion nil t t))))))
>
> Here, the values used only when minibuffer-completion-auto-choose is
> non-nil should be computed only when that variable is non-nil,
> preferably inside the '(when auto-choose' clause.
>
>> @@ -4489,9 +4497,17 @@ minibuffer-choose-completion
>>  If NO-QUIT is non-nil, insert the completion at point to the
>>  minibuffer, but don't quit the completions window."
>>    (interactive "P")
>> -  (with-minibuffer-completions-window
>> -    (let ((completion-use-base-affixes t))
>> -      (choose-completion nil no-exit no-quit))))
>> +  ;; Backported fix for bug#62700
>> +  (let* ((md (completion--field-metadata 
>> (minibuffer--completion-prompt-end)))
>> +         (base-suffix
>> +          (if (eq (alist-get 'category (cdr md)) 'file)
>> +              (buffer-substring (save-excursion (search-forward "/" nil t) 
>> (point))
>> +                                (point-max))
>> +            "")))
>> +    (with-minibuffer-completions-window
>> +      (let ((completion-use-base-affixes t)
>> +            (completion-base-affixes (list (car completion-base-affixes) 
>> base-suffix)))
>> +        (choose-completion nil no-exit no-quit)))))
>
> And here we seem to be modifying code that is not only for when
> minibuffer-completion-auto-choose is non-nil, or what am I missing?

The bug happens regardless of the value of
minibuffer-completion-auto-choose.  It doesn't relate to
minibuffer-completion-auto-choose.