fix branch name

[ikiwiki.git] / doc / todo / allow_plugins_to_add_sorting_methods.mdwn

diff --git a/doc/todo/allow_plugins_to_add_sorting_methods.mdwn b/doc/todo/allow_plugins_to_add_sorting_methods.mdwn
index 21800f4ded3f2d4098e25b099f325aa16be3f3c1..8edc95fb9a2120339a5175403cd4f341923b429b 100644 (file)
--- a/doc/todo/allow_plugins_to_add_sorting_methods.mdwn
+++ b/doc/todo/allow_plugins_to_add_sorting_methods.mdwn
@@ -40,14 +40,26 @@ NIH'd sorting mechanisms:
   interpret `sort="x -y z(w)"` as sorting by (pseudocode)
   `{ $cmp_x->($a, $b) || (-$cmp_y->($a, $b)) || $cmp_z->($a, $b, "w") }`?
 
-## Documentation extracted from the branch
+> I've now added both of these features to the sort-hooks branch. --[[smcv]]
+
+>> I wonder if IkiWiki would benefit from the concept of a "sortspec", like a [[ikiwiki/PageSpec]] but dedicated to sorting lists of pages rather than defining lists of pages?  Rather than defining a sort-hook, define a SortSpec class, and enable people to add their own sort methods as functions defined inside that class, similarly to the way they can add their own pagespec definitions. --[[KathrynAndersen]]
+
+>>> [[!template id=gitbranch branch=smcv/sort-package author="[[Simon_McVittie|smcv]]"]]
+>>> I'd be inclined to think that's overkill, but it wasn't very hard to
+>>> implement, and in a way is more elegant. I set it up so sort mechanisms
+>>> share the `IkiWiki::PageSpec` package, but with a `cmp_` prefix. Gitweb:
+>>> <http://git.pseudorandom.co.uk/smcv/ikiwiki.git?a=shortlog;h=refs/heads/sort-package>
+
+## Documentation from sort-hooks 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
+an existing one.
+
+The callback is given two page names followed by the parameter 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.
 
@@ -57,12 +69,32 @@ For instance, the built-in `title` sort order could be reimplemented as
                pagetitle(basename($_[0])) cmp pagetitle(basename($_[1]));
        }
 
+and to sort by an arbitrary `meta` value, you could use:
+
+       # usage: sort="meta(description)"
+       sub sort_by_meta {
+               my $param = $_[2];
+               error "sort=meta requires a parameter" unless defined $param;
+               my $left = $pagestate{$_[0]}{meta}{$param};
+               $left = "" unless defined $left;
+               my $right = $pagestate{$_[1]}{meta}{$param};
+               $right = "" unless defined $right;
+               return $left cmp $right;
+       }
+
+
 ### 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.
 
+### Multiple sort orders (added to [[ikiwiki/pagespec/sorting]])
+
+In addition, you can combine several sort orders and/or reverse the order of
+sorting, with a string like `age -title` (which would sort by age, then by
+title in reverse order if two pages have the same age).
+
 ### meta title sort parameter (added to [[ikiwiki/directive/meta]])
 
 An optional `sort` parameter will be used preferentially when
@@ -71,3 +103,31 @@ An optional `sort` parameter will be used preferentially when
        \[[!meta title="The Beatles" sort="Beatles, The"]]
 
        \[[!meta title="David Bowie" sort="Bowie, David"]]
+
+## Documentation from sort-package branch
+
+The changes to [[ikiwiki/pagespec/sorting]] are the same.
+The changes to [[plugins/write]] are replaced by:
+
+### Sorting plugins
+
+Similarly, it's possible to write plugins that add new functions as
+[[ikiwiki/pagespec/sorting]] methods. To achieve this, add a function to
+the IkiWiki::PageSpec package named `cmp_foo`, which will be used when sorting
+by `foo` or `foo(...)` is requested.
+
+The function will be passed three or more parameters. The first two are
+page names, and the third is `undef` if invoked as `foo`, or the parameter
+`"bar"` if invoked as `foo(bar)`. It may also be passed additional, named
+parameters.
+
+It should return the same thing as Perl's `cmp` and `<=>` operators: negative
+if the first argument is less than the second, positive if the first argument
+is greater, or zero if they are considered equal. It may also raise an
+error using `error`, for instance if it needs a parameter but one isn't
+provided.
+
+You can also define a function called `check_cmp_foo` in the same package.
+If you do, it will be called while preparing to sort by `foo` or `foo(bar)`,
+with argument `undef` or `"bar"` respectively; it may raise an error using
+`error`, if sorting like that isn't going to work.