[[!tag patch wishlist]]I quite often find myself repeating a boiler-plate
[[ikiwiki/pagespec]] chunk, e.g.

    and !*.png and !*.jpg...

it would be quite nice if I could conveniently bundle them together into a
pagespec "alias", and instead write

    and !image()...

I wrote the following plugin to achieve this:

    commit f3a9dd113338fe5d2b717de1dc69679ff74e2f8d
    Author: Jon Dowland <jmtd@debian.org>
    Date:   Tue May 3 17:40:16 2011 +0100
    
        new plugin: alias.pm - pagespec aliases
    
    diff --git a/IkiWiki/Plugin/alias.pm b/IkiWiki/Plugin/alias.pm
    new file mode 100644
    index 0000000..b8d4574
    --- /dev/null
    +++ b/IkiWiki/Plugin/alias.pm
    @@ -0,0 +1,47 @@
    +package IkiWiki::Plugin::alias;
    +
    +use warnings;
    +use strict;
    +use IkiWiki '3.00';
    +
    +sub import {
    +  hook(type => "getsetup", id=> "alias", call => \&getsetup);
    +  hook(type => "checkconfig", id=> "alias", call => \&checkconfig);
    +}
    +
    +sub getsetup () {
    +    return
    +        plugin => {
    +            description => "allows the definition of pagespec aliases",
    +            safe => 1,
    +            rebuild => 1,
    +            section => "misc",
    +        },
    +        pagespec_aliases => {
    +            type => "string",
    +            example => {"image" => "*jpg or *jpeg or *png or *gif or *ico" },
    +            description => "a set of mappings from alias name to pagespec",
    +            safe => 1,
    +            rebuild => 0,
    +        },
    +}
    +
    +sub checkconfig () {
    +    no strict 'refs';
    +    no warnings 'redefine';
    +
    +    if ($config{pagespec_aliases}) {
    +        foreach my $key (keys %{$config{pagespec_aliases}}) {
    +            my $value = ${$config{pagespec_aliases}}{$key};
    +            # XXX: validate key?
    +            my $subname = "IkiWiki::PageSpec::match_$key";
    +            *{ $subname } = sub {
    +              my $path = shift;
    +              return IkiWiki::pagespec_match($path, $value);
    +            }
    +        }
    +    }
    +}
    +
    +1;

I need to reflect on this a bit more before I send a pull request.  In
particular I imagine the strict/warnings stuff will make you puke.  Also, I'm
not sure whether I should name-grab 'alias' since [[todo/alias_directive]] is
an existing wishlist item.

> I think it would make sense to have "pagespec" in the name somehow.
>
> No, the strict/warnings does not make me puke. Have you read my perl
> code? :-P
> 
> Note that your XXX is right. It would be a security hole to not validate
> `$key`, as anyone with websetup access could cause it to run arbitrary
> perl code.
> 
> Well, except that websetup doesn't currently support configuring hashes
> like used here. Which is a pity, but has led me to try to avoid using
> such hashes in the setup file.
> 
> Have you considered not defining the pagespec aliases in the setup file, but
> instead as directives on pages in the wiki? Using pagestate could store
> up the aliases that have been defined. It could however, be hard to get
> the dependencies right; any page that uses a pagespec containing 
> an alias `foo` would need to somehow depend on the page where the alias
> was defined. --[[Joey]] 

Here's an example setup chunk:

     pagespec_aliases:
       image: "*.png or *.jpg or *.jpeg or *.gif or *.ico"
       helper: "*.css or *.js"
       boring: "image() or helper()"

The above demonstrates self-referential dynamic pagespec aliases.  It doesn't work,
however, to add ' or internal()' to `boring`, for some reason.

-- [[Jon]]

> Probably needs to be `or internal(*)` --[[Joey]] 

> another useful pagespec alias for large maps:

       basewiki: "sandbox or templates or templates/* or ikiwiki or ikiwiki/* or shortcuts or recentchanges or wikiicons/*"

> -- [[Jon]]

>> Useful indeed! --[[Joey]]