Re: project--completing-read-strict breaks ada-mode project completion table

[Dmitry Gutov <dgutov@yandex.ru>]

Hi Stephen,

On 16.01.2019 22:02, Stephen Leake wrote:
> Commit 8f9d93f3054 (Dmitry Gutov   2018-12-29 415) breaks my ada-mode
> completion table.

I'm sorry to hear that, but:

> That commit modifies the completion table by first calling the actual
> completion table to get all the file names, then removing any common
> prefix directory, then calling completing read with that file list.

Yup. It solved a valid user complaint, with a solution proposed by Stefan.

> This violates assumptions made within the ada-mode completion table, and
> breaks the expected completion style - it requires typing the remaining
> directory names first; the ada-mode completion table allows completing
> on the base name only.

TBH, I kind of struggling to understand how the previous version worked 
for you. But I guess when a completion table comes with a strongly 
coupled completion style, it's kind of possible.

> I can understand the motivation behind removing common prefixes, but the
> proper way to do that is to implement a completion style and/or table
> that does that, and make that style/table the default for projects.

How exactly would you propose to do that?

I don't see a way. Styles are an entirely different thing (they don't 
modify how completion strings are presented), and as for a table... for 
one thing, if a table removes a common parent directory from the 
strings, how would it pass that information to the command that's going 
to use it? To expand the file name later on.

> The ada-mode completion style and table eliminates all directories from
> the visible completion string, except the minimum needed to make the
> string unique. I think this is a better solution to the problem;
> project.el should allow the user to choose their prefered solution, by
> choosing a completion style and table.

The user is not choosing a table. The project backend does, and in your 
case it presents an entirely different look for file names from the 
other backends, with no way for the user to change it.

I think that's bad. Namely, that e.g. M-x project-find-file can look 
drastically different for the same user when using different project 
backends.

Far be it from me to criticize the exact "uniquified" look for the 
entries, but I don't think it's a good place to produce them. If it's 
not possible to implement them via a completion style or something like 
that, that would apply to all project backends and their completion 
tables if the user so chooses, maybe it should just be a different 
command. E.g. named project-uniquify-find-file which would modify the 
completion table returned by the project (or, more trivially, the list 
of files). Whereas the completion tables should contain more or less the 
same kind of entries.

IOW, to me this looks like an argument *against* having 
project-file-completion-table be a generic. The project backend should 
produce *data*, not formatting, in the same uniform format, for all 
backends. The more differences there are, the harder it's going to be to 
consume.