[[!template id=gitbranch branch=smcv/sort-hooks author="[[Simon_McVittie|smcv]]"]]
[[!tag patch]]

The available [[ikiwiki/pagespec/sorting]] methods are currently hard-coded in
IkiWiki.pm, making it difficult to add any extra sorting mechanisms. I've
prepared a branch which adds 'sort' as a hook type and uses it to implement a
new `meta_title` sort type.

Someone could use this hook to make `\[[!inline sort=title]]` prefer the meta
title over the page name, but for compatibility, I'm not going to (I do wonder
whether it would be worth making sort=name an alias for the current sort=title,
and changing the meaning of sort=title in 4.0, though).

Gitweb:
<http://git.pseudorandom.co.uk/smcv/ikiwiki.git?a=shortlog;h=refs/heads/sort-hooks>

I briefly tried to turn *all* the current sort types into hook functions, and
have some of them pre-registered, but decided that probably wasn't a good idea.
That earlier version of the branch is also available for comparison:

<http://git.pseudorandom.co.uk/smcv/ikiwiki.git?a=shortlog;h=refs/heads/sort-hooks-excessive>

(The older version is untested, and probably doesn't really work as-is - I
misunderstood the details of how the built-in function `sort` works when using
`$a` and `$b`. The newer version has been tested, and has a regression test for
its core functionality.)

## Documentation extracted from the branch

### sort hook (added to [[plugins/write]])

       hook(type => "sort", id => "foo", call => \&sort_by_foo);

This hook adds an additional [[ikiwiki/pagespec/sorting]] order or overrides
an existing one. The callback is given two page names as arguments, and
returns negative, zero or positive if the first page should come before,
close to (i.e. undefined order), or after the second page.

For instance, the built-in `title` sort order could be reimplemented as

       sub sort_by_title {
               pagetitle(basename($_[0])) cmp pagetitle(basename($_[1]));
       }

### meta_title sort order (conditionally added to [[ikiwiki/pagespec/sorting]])

* `meta_title` - Order according to the `\[[!meta title="foo" sort="bar"]]`
  or `\[[!meta title="foo"]]` [[ikiwiki/directive]], or the page name if no
  full title was set.

### meta title sort parameter (added to [[ikiwiki/directive/meta]])

An optional `sort` parameter will be used preferentially when
[[ikiwiki/pagespec/sorting]] by `meta_title`:

       \[[!meta title="The Beatles" sort="Beatles, The"]]

       \[[!meta title="David Bowie" sort="Bowie, David"]]