Re: [PATCH] Handle case where `beg` and `end` are strings instead of markers

[James N . V . Cash]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> James N. V. Cash [2022-04-29 10:07:33] wrote:
>> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>>> +  (let ((beg (if (number-or-marker-p beg)
>>>> +                 beg
>>>> +               (save-excursion
>>>> +                 (goto-char (minibuffer-prompt-end))
>>>> +                 (search-forward beg))))
>>>> +        (end (if (number-or-marker-p end)
>>>> +                 end
>>>> +               (save-excursion
>>>> +                 (goto-char (point-max))
>>>> +                 (search-backward end)))))
>>>
>>> What if there are several matches for `beg` and/or for `end` in
>>> the buffer?  How do we know we got the intended one?
>>
>> A good question; as far as I can tell though, `beg` and `end` are only
>> strings when called via `choose-completion` in `simple.el`, when it
>> passes in `base-affixes`. `base-affixes` is in turn set to
>> `completion-base-affixes`, which gets set in
>> `minibuffer-completion-help`. There, the value that becomes `beg` is
>> `(buffer-substring (minibuffer--completion-prompt-end) (+ start base-size))`
>> and `end` is `(buffer-substring (point) (point-max))`, so I think that 
>> changing
>> `minibuffer-prompt-end` in my patch to
>> `minibuffer--completion-prompt-end` would suffice to ensure that it is
>> always matching from the correct point to match the intended positions.
>
> I think rather than (minibuffer--completion-prompt-end) and (point-max),
> we should be using "the beginning of the completion area" and "the end
> of the completion area".  In a typical minibuffer completion, that's
> exactly the same, but in `completing-read-multiple` or
> `complete-in-region` the difference can be significant.

In the `completing-read-multiple` case, the `beg` is going to be the
previous completions, so I think this is exactly finding the completion
area (it also seems that `minibuffer--completion-prompt-end` is the same
value as `minibuffer-prompt-end,` it just also raises an error).

In my brief experimentation, it appears `complete-in-region` receives
`beg` and `end` as numbers, so it doesn't go through this searching
stuff at all.

James