bug#70968: 29.2.50; choose-completion on an emacs22-style completion deletes text after point

[Eli Zaretskii]

> Cc: dmitry@gutov.dev, juri@linkov.net
> From: Spencer Baugh <sbaugh@janestreet.com>
> Date: Wed, 15 May 2024 16:26:50 -0400
> 
> 
> try-completion and choose-completion have different behavior; with the
> emacs22 completion style, the former preserves the text after point
> (while ignoring it), whereas the latter deletes the text after point.
> 
> 1. emacs -Q
> 
> 2. In scratch, type "inhibit-asdf" and move point to after the "-"
> 
> 3. Type "q" and M-<tab>
>    The buffer now contains "inhibit-quitasdf", because the emacs22 style
>    ignored the text after point and completed on "inhibit-q".
> 
> 4. C-/ C-/ to change the buffer back to "inhibit-asdf"
> 
> 5. M-<tab>
>    The *Completions* buffer will be displayed, containing among others
>    "inhibit-quit" as a completion, because the emacs22 style ignored the
>    text after point and completed on "inhibit-".
> 
> 6. Use M-<down> and M-<ret> to select and choose "inhibit-quit"
>    The buffer now contains "inhibit-quit".
> 
> The two ways of selecting completions should behave the same.
> 
> I suggest that the behavior of not deleting the text after point is
> better.  The emacs22 style takes care to not delete the text after point
> in try-completion and in completion cycling; we should take similar care
> in choose-completion.

If making these two ways consistent means we need to change the
behavior of emacs22 style of completion, then I'm sorry, but we cannot
do that.  This style is a legacy style, and is there to provide the
legacy behavior for those who need it.

So for making the decisions in this case we need to know how did Emacs
22 and later versions behave in the above scenario, and take it from
there.  If they all behaved like you show, then this behavior must
stay unchanged, unfortunately, for backward-compatibility reasons.