I've found myself wanting to know which [[plugins]] are switched on so I know which pre-processor commands I can use.  The attached [[patch]] adds a new plugin that generates the list of available plugins. -- [[Will]]

> Good idea, I do see a few problems:
> 
> - preprocessor directives do not necessarily have the same name as the
>   plugin that contains them (for example, the graphviz plugin adds a graph
>   directive). Won't keys `%{IkiWiki::hooks{preprocess}}` work?

>>> Er, yeah - that's a much better solution. :) -- and done

> - "listplugins" is a bit misnamed since it only does preprocessor directives.

>>> Yes.  Initially this was going to list all enabled plugins.  Then when searching
>>> for enabled plugins I changed my mind and decided that a list of pre-processor
>>> directives was more useful.  I'll fix that too. -- changed to `listpreprocessors`

> - comment was copied from version plugin and still mentions version :-)

>>> :-) -- fixed

> - Seems like [[ikiwiki/formatting]] could benefit from including the
>   list.. however, just a list of preprocessor directive names is not
>   the most user-friendly thing that could be put on that page. It would
>   be nice if there were also a short description and maybe an example of
>   use. Seems like the place to include that info would be in the call
>   to `hook()`.
>   (Maybe adding that is more involved than you want to go though..)
> 
> --[[Joey]]

>> Adding a whole new hook for a usage example is more effort than I
>> wanted to go to.  I was thinking of either:

>>> Just to clarify, I meant adding new parameters to the same hook call
>>> that registers the plugin. --[[Joey]]

>>    - Adding a configuration for a wiki directory.  If a matching page is in the
>>      specified wiki directory then the plugin name gets turned into a link to that
>>      page
>>    - Adding configuration for an external URL.  Each plugin name is added as
>>       a link to the plugin name appended to the URL.

>>The first option is easier to navigate and wouldn't produce broken links,
>>but requires all the plugin documentation to be local.  The second option
>>can link back to the main IkiWiki site, but if you have any non-standard
>>plugins then you'll get broken links.
>>
>>Hrm.  After listing all of that, maybe your idea with the hooks is the better
>>solution.  I'll think about it some more. -- [[Will]]

>>> I've also run into this problem with the websetup plugin, and
>>> considered those ideas too. I don't like the external url, because
>>> ikiwiki.info may be out of sync with the version of ikiwiki being used.
>>> (Or maybe it's gone! :-) The first idea is fine, except for the bloat
>>> issue. If turning on listpreprocessors and/or websetup means adding
>>> hundreds of pages (and of kilobytes) to your wiki, that could be an
>>> incentive to not turn them on..
>>>
>>> Hmm.. maybe the thing to do is to use _internal pages for the plugins;
>>> then the individual pages would not be rendered, and your inlines would
>>> still work. Although I don't know how websetup would use it then, and
>>> also they would have to be non-internal for ikiwiki's own docwiki. Hmm.
>>> Maybe these are two different things; one is a set of pages describing
>>> preprocessor directives, and the second a set of pages describing
>>> plugins. They're so closely related though it seems a shame to keep
>>> them separate..
>>> --[[Joey]]

>>> I started implementing the hook based solution, and decided I didn't like
>>> it because there was no nice way to rebuild pages when the preprocessor
>>> descriptions changed.  So instead I assumed that the the [[plugins]] pages
>>> would be moved into the underlay directory.  This plugin then uses an
>>> `inline` directive to include those pages.  You can use the `inline`
>>> parameter to decide if you want to include all the descriptions or
>>> just the titles.  There is also an option to auto-create default/blank
>>> description pages if they are missing (from a template).  As preprocessor
>>> commands don't list unless they have a description page, auto-creation
>>> is enabled by default.
>>>
>>>  There are three new templates that are needed.  These are for:
>>>
>>>  - The auto-created description pages are generated from `preprocessor-description.tmpl`.
>>>  - When only pre-processor names are listed, the `listpreprocessors-listonly.tmpl` template is used.
>>>  - When pre-processor descriptions are included inline, the `listpreprocessors-inline.tmpl` template is used.
>>>
>>> -- [[Will]]

>>>> Just a quick note: pages are only created for pre-processor commands
>>>> that exist when the `refresh` hook is called.  This is before the [[shortcuts]] are
>>>> processed.  However, the list of available pre-processor commands will include
>>>> shortcuts if they have description pages (the list is generated later, after the
>>>> shortcuts have been added).  While this was unplanned, it seems a reasonable
>>>> tradeoff between including all the large number of shortcuts and including none. -- [[Will]]

>>>>>> I think that using an inline is elegant! However, I don't understand
>>>>>> why it has to create stub description pages? I doubt that, if a
>>>>>> directive is missing a page, the stub will be filled out in many
>>>>>> wikis. And it adds a lot of complexity, particularly committing a
>>>>>> bunch of generated pages to revision control when the user just
>>>>>> wants a plugin list seems undesirable.
>>>>>>
>>>>>> Seems to me it could use the inline for pages that exist, and append
>>>>>> to the bottom a generated text for anything that is currently missing.
>>>>>> The generated text could even have a page creation link in it if
>>>>>> you wanted.
>>>>>> --[[Joey]]

>>>>>>> I kinda agree about the page generation.  I don't like mixing an
>>>>>>> inlined and a list though.  Besides which, that ends
>>>>>>> up keeping much of complexity of the page generation because
>>>>>>> the code still has to detect which pages are missing.  I've added
>>>>>>> a patch that uses a list of wikilinks instead.  This way available
>>>>>>> pages get linked correctly, and missing pages get normal creation
>>>>>>> links.  The old patch is still here if you decide you prefer that. -- [[Will]]

>>>>>>>> Can you explain the full/early list (why track both?) and generated parameter?

>>>>>>>>> If you add in all the shortcuts you get quite a long list.  My original idea
>>>>>>>>> was to just track the plugin commands.  This is the early list.  But then
>>>>>>>>> I thought that it might be nice for someone looking at wiki source and
>>>>>>>>> seeing a shortcut to know where it came from.  So I decided to make
>>>>>>>>> displaying the full list an option, with the original concept as the default.

>>>>>>>>> Another option here might be to generate the full list every time, but give
>>>>>>>>> generated pre-processor commands (e.g. shortcuts) a different css class.
>>>>>>>>> I'm not sure that is better than what I have though. 

>>>>>>>>> I keep track of both in the page state because if a command moves from
>>>>>>>>> a shortcut to the early list (or vice versa) it changes what should be
>>>>>>>>> displayed in the default use of the plugin.  I thought about tracking just what
>>>>>>>>> was actually used on the page, but I don't know in the needsbuild hook whether the `generated`
>>>>>>>>> parameter has been supplied (or maybe the plugin is used twice on the page -
>>>>>>>>> once in each form).  It was just easier to track both.

>>>>>>>> Only code change I'd suggest is using `htmllink` rather than 
>>>>>>>> generating a wikilink.

>>>>>>>>> Yeah - that would make sense.  done. -- [[Will]]

    #!/usr/bin/perl
    # Ikiwiki listpreprocessors plugin.
    package IkiWiki::Plugin::listpreprocessors;
    
    use warnings;
    use strict;
    use IkiWiki 2.00;
    
    sub import { #{{{
    	hook(type => "getsetup", id => "listpreprocessors", call => \&getsetup);
    	hook(type => "checkconfig", id => "listpreprocessors", call => \&checkconfig);
    	hook(type => "needsbuild", id => "listpreprocessors", call => \&needsbuild);
    	hook(type => "preprocess", id => "listpreprocessors", call => \&preprocess);
    } # }}}
    
    sub getsetup () { #{{{
    	return
    		plugin => {
    			safe => 1,
    			rebuild => undef,
    		},
    		preprocessor_description_dir => {
    			type => "string",
    			description => "The ikiwiki directory that contains plugin descriptions.",
    			safe => 1,
    			rebuild => 1,
    		},
    } #}}}
    
    my @fullPluginList;
    my @earlyPluginList;
    my $pluginString;
    
    sub checkconfig () { #{{{
        if (!defined $config{plugin_description_dir}) {
            $config{plugin_description_dir} = "ikiwiki/plugin/";
        }
    
        @earlyPluginList = sort( keys %{ $IkiWiki::hooks{preprocess} } );
    } #}}}
    
    sub needsbuild (@) { #{{{
    	my $needsbuild=shift;
    
    	@fullPluginList = sort( keys %{ $IkiWiki::hooks{preprocess} } );
    	$pluginString = join (' ', @earlyPluginList) . " : ". join (' ', @fullPluginList);
    
    	foreach my $page (keys %pagestate) {
    		if (exists $pagestate{$page}{listpreprocessors}{shown}) {
    			if ($pagestate{$page}{listpreprocessors}{shown} ne $pluginString) {
    				push @$needsbuild, $pagesources{$page};
    			}
    			if (exists $pagesources{$page} &&
    					grep { $_ eq $pagesources{$page} } @$needsbuild) {
    				# remove state, will be re-added if
    				# the [[!listpreprocessors]] is still there during the
    				# rebuild
    				delete $pagestate{$page}{listpreprocessors}{shown};
    			}
    		}
    	}
    } # }}}
    
    sub preprocess (@) { #{{{
    	my %params=@_;
    	
    	$pagestate{$params{destpage}}{listpreprocessors}{shown}=$pluginString;
    	
    	my @pluginlist;
    	
    	if (defined $params{generated}) {
    		@pluginlist = @fullPluginList;
    	} else {
    		@pluginlist = @earlyPluginList;
    	}
    	
    	my $result = '<ul class="listpreprocessors">';
    	
    	foreach my $plugin (@pluginlist) {
    		$result .= '<li class="listpreprocessors">';
    		$result .= htmllink($params{page}, $params{destpage}, IkiWiki::linkpage($config{plugin_description_dir} . $plugin));
    		$result .= '</li>';
    	}
    	
    	$result .= "</ul>";
    
    	return $result;
    } # }}}
    
    1

----

Here is the main listpreprocessors plugin. (Note, because this has double
square brackets in the source, it isn't quite displaying correctly - look
at the page source for details.)  New template files follow:

    #!/usr/bin/perl
    # Ikiwiki listpreprocessors plugin.
    package IkiWiki::Plugin::listpreprocessors;
    
    use warnings;
    use strict;
    use Encode;
    use IkiWiki 2.00;
    
    sub import { #{{{
    	hook(type => "getsetup", id => "listpreprocessors", call => \&getsetup);
    	hook(type => "preprocess", id => "listpreprocessors", call => \&preprocess);
    	hook(type => "refresh", id => "listpreprocessors", call => \&refresh);
    } # }}}
    
    sub getsetup () { #{{{
    	return
    		plugin => {
    			safe => 1,
    			rebuild => undef,
    		},
    		preprocessor_description_dir => {
    			type => "string",
    			description => "The ikiwiki directory that contains plugin descriptions.",
    			safe => 1,
    			rebuild => 1,
    		},
    		preprocessor_description_autocreate => {
    			type => "boolean",
    			description => "Should pre-processor command descriptions be automatically created from a template.",
    			safe => 1,
    			rebuild => 1,
    		},
    } #}}}
    
    sub gendescription ($$) { #{{{
    	my $plugin=shift;
    	my $page=shift;
    	my $file=$page.".".$config{default_pageext};
    	my $template=template("preprocessor-description.tmpl");
    	$template->param(page => $page, plugin => $plugin);
    	writefile($file, $config{srcdir}, $template->output);
    	if ($config{rcs}) {
    		IkiWiki::rcs_add($file);
    	}
    } #}}}
    
    sub refresh () { #{{{
    	eval q{use File::Find};
    	error($@) if $@;
    
    	if (defined $config{preprocessor_description_autocreate} && ! $config{preprocessor_description_autocreate}) {
    		return;	# create pages unless they explicitly ask us not to
    	}
    
    	if (!defined $config{preprocessor_description_dir}) {
    		$config{preprocessor_description_dir} = "ikiwiki/plugin/";
    	}
    	
    	my @pluginlist = sort( keys %{ $IkiWiki::hooks{preprocess} } );
    	my %pluginpages;
    
    	if (@pluginlist) {
    		my ($plugin,$page);
    		
    		foreach $plugin (@pluginlist) {
    			$pluginpages{$plugin} = $config{preprocessor_description_dir} . $plugin;
    		}
    
    		my %pages;
    		foreach my $dir ($config{srcdir}, @{$config{underlaydirs}}, $config{underlaydir}) {
    			find({
    				no_chdir => 1,
    				wanted => sub {
    					$_=decode_utf8($_);
    					if (IkiWiki::file_pruned($_, $dir)) {
    						$File::Find::prune=1;
    					}
    					elsif (! -l $_) {
    						my ($f)=/$config{wiki_file_regexp}/; # untaint
    						return unless defined $f;
    						$f=~s/^\Q$dir\E\/?//;
    						return unless length $f;
    						return if $f =~ /\._([^.]+)$/; # skip internal page
    						if (! -d _) {
    							$pages{pagename($f)}=$f;
    						}
    					}
    				}
    			}, $dir);
    		}
    
    		if ($config{rcs}) {
    			IkiWiki::disable_commit_hook();
    		}
    		
    		my $needcommit = 0;
    		
    		while (($plugin,$page) = each %pluginpages) {
    			if (! exists $pages{$page}) {
    				$needcommit = 1;
    				gendescription($plugin,$page);
    			}
    		}
    		
    		if ($config{rcs}) {
    			if ($needcommit) {
    				IkiWiki::rcs_commit_staged(
    					gettext("automatic pre-processor description generation"),
    					undef, undef);
    			}
    			IkiWiki::enable_commit_hook();
    		}
    	}
    } #}}}
    
    sub preprocess (@) { #{{{
    	my %params=@_;
    	
    	if (!defined $config{plugin_description_dir}) {
    		$config{plugin_description_dir} = "ikiwiki/plugin/";
    	}
    	
    	my @pluginlist = sort( keys %{ $IkiWiki::hooks{preprocess} } );
    	foreach my $plugin (@pluginlist) {
    		$plugin = $config{plugin_description_dir} . $plugin;
    	}
    	my $pluginString = join (' or ', @pluginlist);
    	
    	my $result = "[[!inline pages=\"$pluginString\" feeds=\"no\" show=0 sort=\"title\"";
    	
    	if (defined $params{inline}) {
    		$result .= ' template=\"listpreprocessors-listonly\" archive="yes"';
    	} else {
    		$result .= ' template=\"listpreprocessors-inline\" archive="no"';
    	}
    	
    	$result .= "]]";
    	
    	return IkiWiki::preprocess($params{page}, $params{destpage}, 
    		IkiWiki::filter($params{page}, $params{destpage}, $result));
    } # }}}
    
    1

--------

This is what I was using for `listpreprocessors-inline.tmpl`:

    <div class="listpreprocessorsinline">
    
    <div class="inlineheader">
    
    <span class="header">
    <a href="<TMPL_VAR PAGEURL>"><TMPL_VAR TITLE></a>
    </span>
    
    </div><!--.inlineheader-->
    
    <div class="inlinecontent">
    <TMPL_VAR CONTENT>
    </div><!--.inlinecontent-->
    
    </div><!--.listpreprocessorsinline-->

--------

This is what I was using for `listpreprocessors-listonly.tmpl`:

    <p class="listpreprocessors"><a href="<TMPL_VAR PAGEURL>"><TMPL_VAR TITLE></a></p>

--------

This is what I was using for `preprocessor-description.tmpl`:

    The <TMPL_VAR plugin> preprocessor command currently has no description.
    
    Maybe you should edit this page to add one.