bug#48356: 28.0.50; choose-completion discards the suffix after the completion boundary

[Dmitry Gutov <dmitry@gutov.dev>]

On 10/04/2024 05:38, Stefan Monnier wrote:
>>>> ...which translates to "/" because of the double slash -- the filesystem
>>>>    root directory (*). But that's the same data which would be used by any
>>>>    other proposed solution, too.
>>> More or less, tho the "ideal" solution is to do that in the
>>> completion-style code, which has a bit more knowledge about it.
>> Doing it in completion-style, though, would either require a relatively
>> awkward change in most/all styles (e.g. the "new dynamic variable" route),
>> or a more straightforward change in styles together with an incompatible
>> change in completion-all-completions.
> 
> Yup, hence the quotes around "ideal".
> 
>> So on balance, would you say it's a good idea to a) use this approach in
>> minibuffer-completion-help, b) create a named function for it, for other
>> callers to take advantage of it as well?
> 
> Yes, while waiting for a new API it seems like a good stop gap.
> 
>> Looks like completion--merge-suffix is the helper to use.
> 
> Yup.
> 
>>> In theory this approach can "do the wrong thing" with some completion
>>> styles, but AFAIK they haven't been written yet.  🙂
>> So you figure that such theoretical style would return adjusted base-suffix
>> in -all-completions method, not just in -try-completion?
> 
> A completion style could make use of (and list) things after the
> boundary.  E.g. completing a file name like
> 
>      foo/ba<|>ar/baz
> 
> could decide to list all the files that match
> 
>      *f*o*o*/*b*a*a*r*/*b*a*z*
> 
> in which case the "end boundary" of the `completion-all-completions`
> output should not be the `cdr` of the `completion-boundaries`.
> 
> I wouldn't worry about it, tho.

All right, please see the new function completion-base-suffix added in 
0288bc6c949. Any docstring improvements (and others) are welcome.

I guess we should also mention it in NEWS...