Substring matching for info index command

Substring matching for info index command

[Tom]

I've never used the builtin completion-styles, because I 
use other completion packages, but I thought I give it a try
and try substring matching for the info index command.

I added this advice to the command which wraps it in a
let and sets completion-styles to substring:

(defadvice Info-index (around my-Info-index activate)
  (let ((completion-styles '(substring)))
    ad-do-it))


However, it has no effect, it still uses the prefix
completion style. Why is that?

RE: Substring matching for info index command

[Drew Adams]

> I've never used the builtin completion-styles, because I
> use other completion packages, but I thought I give it a try
> and try substring matching for the info index command.
> 
> I added this advice to the command which wraps it in a
> let and sets completion-styles to substring:
> 
> (defadvice Info-index (around my-Info-index activate)
>   (let ((completion-styles '(substring)))
>     ad-do-it))
> 
> However, it has no effect, it still uses the prefix
> completion style. Why is that?

The reason is that `Info-index' uses your input not only
to match against the possible completions but also (and
first) to come up with (calculate/find) the possible
completions.

And when it uses your input to gather the possible
completions it simply searches the indexes of the manual
for your input, prefixed by `* '.

In other words, the problem is not with completion; it is
with the way `Info-index' gathers the completion candidates
from the indexes.  It does that by simply searching for
your input, as a prefix (prepended by `* ', which is what
is on the index-entry line in the index.

For example, in the Emacs manual, node `Command Index',
there is an entry that looks like this:

* ask-user-about-lock

When you type `user' as input, `Info-index' searches all
of the indexes for this regexp:

"
\\* +\\([^
]*\\(user\\)[^
]*\\):[ 	]+\\([^
]*\\)\\.\\(?:[ 	
]*(line +\\([0-9]+\\))\\)?"

which is essentially a search for `* user'.

It is only after gathering all matches for this regexp,
across all indexes, that `Info-index' presents them to you,
providing completion (substring completion, in your case).

In sum, you would need to rewrite `Info-index' or heavily
advise it, to get it to DTRT.

Or you can just use Icicles.  `i user S-TAB' shows these
index-entry completion candidates for the Emacs manual:

--user
ange-ftp-default-user
apropos-user-option 
ask-user-about-lock
backup, and user-id
GDB User Interface layout 
load init file of another user
mail-user-agent
package-user-dir 
USER
user name for remote file access
user option 
user options, changing
user-full-name
user-mail-address 
user-mail-address <1>
user-mail-address, initialization 

Re: Substring matching for info index command

[Tom]

Drew Adams <drew.adams <at> oracle.com> writes:
> 
> In other words, the problem is not with completion; it is
> with the way `Info-index' gathers the completion candidates
> from the indexes.  It does that by simply searching for
> your input, as a prefix (prepended by `* ', which is what
> is on the index-entry line in the index.


Thanks for your investigation, but why should info use
my input to gather completion candidates? It should
gather all candiates and pass them them to 
completing-read, shouldn't it?

Isn't it a bug? Incosistent behavior with the
builtin completion-styles?

RE: Substring matching for info index command

[Drew Adams]

> > In other words, the problem is not with completion; it is
> > with the way `Info-index' gathers the completion candidates
> > from the indexes.  It does that by simply searching for
> > your input, as a prefix (prepended by `* ', which is what
> > is on the index-entry line in the index.
> 
> Thanks for your investigation, but why should info use
> my input to gather completion candidates? 

I didn't say that it should.  I said that it does.
Feel free to file a bug report: `M-x report-emacs-bug'.

> It should gather all candiates and pass them them to
> completing-read, shouldn't it?
> Isn't it a bug? Incosistent behavior with the
> builtin completion-styles?

My opinion?  Yes.  (And that's what Icicles does.)

Re: Substring matching for info index command

[Eli Zaretskii]

> From: Tom <adatgyujto@gmail.com>
> Date: Sun, 7 Dec 2014 12:15:52 +0000 (UTC)
> 
> I've never used the builtin completion-styles, because I 
> use other completion packages, but I thought I give it a try
> and try substring matching for the info index command.

info.el already does that: it first searches for the string at the
beginning of the index entries, and then anywhere inside the entries.

Re: Substring matching for info index command

[Stefan Monnier]

> I've never used the builtin completion-styles, because I 
> use other completion packages, but I thought I give it a try
> and try substring matching for the info index command.

Info should setup a "completion category" so you could configure this
via `completion-category-overrides'.  Please M-x report-emacs-bug.

> I added this advice to the command which wraps it in a
> let and sets completion-styles to substring:

> (defadvice Info-index (around my-Info-index activate)
>   (let ((completion-styles '(substring)))
>     ad-do-it))

That affects the body of the function (i.e. the code that, given
a query, will look for the corresponding place in the index), whereas
you want to tweak the way the interactive-spec works.

You might like to try something like (guaranteed 100% untested):

   (advice-add 'Info-index :before
               (lambda (&rest _)
                 (interactive
                   (lambda (spec)
                     (let ((completion-styles '(substring)))
                       (advice-eval-interactive-spec spec))))
                 nil))
                             
-- Stefan