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

[Dmitry Gutov <dmitry@gutov.dev>]

On 14/09/2024 12:17, Eli Zaretskii wrote:
> B. Deprecate the emacs22 style and replace it with a new style called
>     `ignore-suffix` which has this bug fixed, and which replaces emacs22
>     in the default value of completion-styles.

Note that while this is a viable option, we're still lacking a mechanism 
which would fix the problem for the new completion style.

And then we'd have two code paths for this behavior that somehow need to 
distinguish between these styles.

With the original proposal we would delegate to the style's completion 
logic, but it would apparently behave the same between emacs22 and the 
new style.

> Option C is from my POV the least desirable one: it adds some
> complicated logic, which will almost certainly produce unintended
> results, as everything in this completion-related mess we have.

That's probably true, but whether it will make things more complicated 
or not would also depend on the overall design. With some effort, it 
could be the opposite - but with more changes across the board, overall 
not backward compatible ones.

> I'm okay with adding a new style, per B, but why do we need to
> deprecate emacs22 at the same time?  Let users who want this new
> behavior customize their completion styles to use this new style
> instead of emacs22.

I don't envy the person who's going to write documentation and has to 
describe the distinction between these two styles, that they differ in 
this particular place of the UI, and are otherwise the same.

Deprecating the old style would at least say that this complication is a 
wart which would someday go away, and we could take a shortcut in the 
implementation (e.g. hardcode the value `emacs22` in some check).