bug#20365: 24.5; all-completions returns duplicates for Info-read-node-name-1

[Oleh Krehel <ohwoeowho@gmail.com>]

On Sat, Apr 18, 2015 at 7:41 PM, Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
> Just a first comment: it's not considered incorrect for
> `all-completions' to return a list with duplicate entries in it.
> More specifically, it's considered the completion UI's job to remove
> those duplicates.
>
>>   (setq x (all-completions "(" 'Info-read-node-name-1))
>> x will contain many duplicates for each node, like "org" "org" "org"
>> "org" "org.info.gz" "org" "org.info.gz" "org" "org.info.gz".
>
> Maybe the way these entries are generated could be reviewed to try and
> reduce the number of duplicates.  And we could call `delete-dups' on the
> result: while a completion-table shouldn't need to go out of its way to
> reduce the number of duplicates (since the UI is supposed to handle it
> anyway), it's probably good to avoid having such expected large number of
> duplicates, indeed.
>
>> Finally, if one of the elements of `all-completions' is passed, it still
>> doesn't work.
>
> What does "is passed" mean here?  What does "doesn't work" mean here?
>
>> I'm guessing that it expects "(org)" instead of "org", but
>> then why not offer these on the completion list?
>
> What is "it"?

What I think is happening there is that Info calls
`completing-read-function' and ultimately gives it (through
all-completions) a list like '("org" "emacs"...).  And then it expects
the answer to be in the form "(org)" or "(emacs)". Which I think is
strange. I've pushed recently this hack to `ivy-read', which makes
it work for Info:

((eq collection 'Info-read-node-name-1)
 (if (equal Info-current-file "dir")
     (setq collection
           (mapcar (lambda (x) (format "(%s)" x))
                   (cl-delete-duplicates
                    (all-completions "(" collection predicate)
                    :test 'equal)))
   (setq collection (all-completions "" collection predicate))))

This is quite ugly to go to such lengths to deal with just one
completion case.

Oleh