bug#54374: 29.0.50; previous-completion fails at beginning of completions buffer

[Philip Kaludercic]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Philip Kaludercic <philipk@posteo.net>
>> Cc: juri@linkov.net,  54374@debbugs.gnu.org
>> Date: Mon, 14 Mar 2022 08:20:29 +0000
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> >> From: Philip Kaludercic <philipk@posteo.net>
>> >> Date: Sun, 13 Mar 2022 20:39:53 +0000
>> >> Cc: 54374@debbugs.gnu.org
>> >> 
>> >> -      (while (< n 0)
>> >> +      (while (and (< n 0) (< 1 (point)))
>> >
>> > Please always use point-min, never a literal 1.
>> 
>> Can do, but does it make a difference in this case?  The only reason the
>> comparison is made is so that (1- (point)) doesn't return an invalid
>> point value.
>
> Any buffer position outside of the accessible portion of the buffer is
> almost always invalid; the number of APIs which tolerate such values
> of buffer position is very small.
>
> Here, try this:
>
>   emacs -Q
>   M-: (narrow-to-region 20 (point-max)) RET
>   M-: (get-text-property 1 'mouse-face) RET
>
> You will get the same args-out-of-range error.  That's because
> get-text-property validates the position against the accessible
> portion of the buffer, not against some absolute values.

I didn't know that, thank you for the background information!

-- 
        Philip Kaludercic