function injection overhaul

Add an inject function, that can be used by plugins that want to replace
one of ikiwiki's functions with their own version. (This is a scary thing
that grubs through the symbol table, and replaces all exported occurances
of a function with the injected version.)

external: RPC functions can be injected to replace exported functions.

Removed the stupid displaytime hook, and use injection instead.

2 files changed, 55 insertions, 0 deletions

diff --git a/doc/plugins/contrib/po.mdwn b/doc/plugins/contrib/po.mdwn
index 30ede95a6..c4b7f9ee9 100644
--- a/doc/plugins/contrib/po.mdwn
+++ b/doc/plugins/contrib/po.mdwn
@@ -47,6 +47,11 @@ Any thoughts on this?
 >>> `targetpage`, `bestlink`, and `beautify_urlpath`. But, I noticed
 >>> the other day that such wrappers around exported functions are only visible by
 >>> plugins loaded after the plugin that defines them.
+>>> 
+>>> Update: Take a look at the new "Function overriding" section of
+>>> [[plugins/write]]. I think you can just inject wrappers about a few ikiwiki
+>>> functions, rather than adding hooks. The `inject` function is pretty
+>>> insane^Wlow level, but seems to work great. --[[Joey]]
 >>
 >> The Discussion pages issue is something I am not sure about yet. But I will
 >> probably decide that "slave" pages, being only translations, don't deserve
diff --git a/doc/plugins/write.mdwn b/doc/plugins/write.mdwn
index 856b34ba1..2e11e6234 100644
--- a/doc/plugins/write.mdwn
+++ b/doc/plugins/write.mdwn
@@ -854,6 +854,56 @@ By the way, to parse a ikiwiki setup file and populate `%config`, a
 program just needs to do something like:
 `use IkiWiki::Setup; IkiWiki::Setup::load($filename)`
 
+### Function overriding
+
+Sometimes using ikiwiki's pre-defined hooks is not enough. Your plugin
+may need to replace one of ikiwiki's own functions with a modified version,
+or wrap one of the functions.
+
+For example, your plugin might want to override `displaytime`, to change
+the html markup used when displaying a date. Or it might want to override
+`IkiWiki::formattime`, to change how a date is formatted. Or perhaps you
+want to override `bestlink` and change how ikiwiki deals with WikiLinks.
+
+By venturing into this territory, your plugin is becoming tightly tied to
+ikiwiki's internals. And it might break if those internals change. But
+don't let that stop you, if you're brave.
+
+Ikiwiki provides an `inject()` function, that is a powerful way to replace
+any function with one of your own. This even allows you to inject a
+replacement for an exported function, like `bestlink`. Everything that
+imports that function will get your version instead. Pass it the name of
+the function to replace, and a new function to call. 
+
+For example, here's how to replace `displaytime` with a version using HTML 5
+markup:
+
+	inject(name => 'IkiWiki::displaytime', call => sub {
+		return "<time>".formattime(@_)."</time>";
+	});
+
+Here's how to wrap `bestlink` with a version that tries to handle
+plural words:
+
+	my $origbestlink=\&bestlink;
+	inject(name => 'IkiWiki::bestlink', call => \&mybestlink);
+
+	sub deplural ($) {
+		my $word=shift;
+		$word =~ s/e?s$//; # just an example :-)
+		return $word;
+	}
+
+	sub mybestlink ($$) {
+		my $page=shift;
+		my $link=shift;
+		my $ret=$origbestlink->($page, $link);
+		if (! length $ret) {
+			$ret=$origbestlink->($page, deplural($link));
+		}
+		return $ret;
+	}
+
 ### Javascript
 
 Some plugins use javascript to make ikiwiki look a bit more web-2.0-ish.