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

[Dmitry Gutov <dmitry@gutov.dev>]

On 16/05/2024 11:13, Eli Zaretskii wrote:
>> 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.

I don't think that would be required exactly.

The problem here (IIUC) is that completion behaves differently with the 
emacs22 style depending on whether the execution path went through 
choose-completion (which is not a method of completion style but a 
common subroutine) or not (when completion--do-completion performed 
expansion).