Re: Emacs completion matches selection UI

[Dmitry Gutov <dgutov@yandex.ru>]

On 04.01.2014 07:54, Stefan Monnier wrote:
>> In `company-capf', we iterate though the completion-at-point-functions each
>> time. This works, and works well enough, since the "does it fit" code is
>> usually fast, but it looks fairly bizarre to me, logically.
>
> Agreed.  It was just "the easy" way to fit it in.

Can't we save the last `company--capf-data' value in the `prefix' case? 
Company only calls the rest of the cases after it, and only when the 
returned value is non-nil. Since prefix value has to stay fresh, the 
cached data will also be.

> "The right thing" would be to replace company-backends with
> completion-at-point-functions.

I'm not convinced yet that it's the right thing to do.

a) `c-a-p-f' looks less accessible to the end user than 
`company-backends', and the former isn't even a defcustom. The structure 
of the latter, on the other hand, is easier to read and modify in users' 
init files and major mode hooks.

The Company backends are also easier to spot among other functions in 
the packages that contain them. The names of the c-a-p-functions used by 
e.g. IELM follow no discernible convention.

b) There's no direct analog to "merged" Company backends in 
`completion-at-point-functions'. `company-backends' can contain list 
values, and `company--multi-backend-adapter' handles the merging of the 
returned data.

I'm also tinkering with the idea to make individual candidates remember 
the backends they came from (using text properties, most likely), so 
that we will know which backend's function to use with this candidate. 
Calling `post-completion' action from the wrong backend would be the 
best example of how it's currently broken.