doc/todo/conditional_text_based_on_ikiwiki_features.mdwn



I'd like to see some way to conditionally include wiki text based on
whether the wiki enables or disables certain features.  For example,
[[helponformatting]], could use \[[if (enabled smiley) """Also, because this wiki has the smiley plugin enabled, you can insert \[[smileys]] and some other useful symbols."""]], and a standard template for [[plugins]]
pages could check for the given plugin name to print "enabled" or
"disabled".
Some potentially useful conditionals:

enabled pluginname
disabled pluginname
any pagespec: true if any of the pages in the [[PageSpec]] exist
all pagespec: true if all of the pages in the [[PageSpec]] exist
no pagespec or none pagespec: true if none of the pages in the [[PageSpec]] exist
thispage pagespec: true if pagespec includes the page getting rendered (possibly one including the page with this content on it).
sourcepage pagespec: true if pagespec includes the page corresponding to the file actually containing this content, rather than a page including it.
included: true if included on another page, via [[plugins/inline]], [[plugins/sidebar]], [[plugins/contrib/navbar]], etc.

You may or may not want to include boolean operations (and, or, and
not); if you do, you could replace disabled with not enabled, and no pagespec or none pagespec with not any pagespec (but you may want to
keep the aliases for simplicity anyway).  You also may or may not want to
include an else clause; if so, you could label the text used if true as
then.
Syntax could vary greatly here, both for the [[PreprocessorDirective]] and
for the condition itself.

I think this is a good thing to consider, although conditionals tend to
make everything a lot more complicated, so I also want to KISS, and not
use too many of them.
I'd probably implement this using the same method as pagespecs, so 'and',
'or', '!', and paren groupings work.
It could be thought of as simply testing to see if a pagespec matches
anything, using a slightly expanded syntax for the pagespec, which would
also allow testing for things like link(somepage),
created_before(somepage), etc.
That also gives us your "any pagespec" for free: "page or page or page".
And for "all pagespec", you can do "page and page and page".
For plugins testing, maybe just use "enabled(name)"?
I'm not sure what the use cases are for thispage, sourcepage, and
included. I don't know if the included test is even doable. I'd be
inclined to not bother with these three unless there are use cases I'm
not seeing.
As to the syntax, to fit it into standard preprocessor syntax, it would
need to look something like this:
[[if test="enabled(smiley)" """foo"""]]
--[[Joey]]


[[PageSpec]] syntax seems perfect, and your proposed syntax for the if
[[PreprocessorDirective]] looks fine to me.
[[PageSpec]]s don't give you none for free, since !foo/* as a boolean
would mean "does any page not matching foo/* exist", not "does foo/*
match nothing"; however, I don't really care much about none, since I
just threw it in while brainstorming, and I don't know any compelling use
cases for it.
enabled(pluginname) will work perfectly, and !enabled(pluginname)
makes disabled unnecessary.
A few use cases for included, which I would really like to see:


On the sidebar page, you could say something like [[if test="!included"
"""This page, without this help message, appears as a sidebar on all
pages."""]].  The help text would then only appear on the sidebar page
itself, not the sidebar included on all pages.


On [[blog]] entries, you could use included to implement a cut.
(Please don't take that as an argument against. :) ) For instance, you
could use included rather than [[plugins/toggle]] for the detailed
changelogs of ikiwiki, or to embed an image as a link in the feed rather
than an embedded image.


Some use cases for thispage:


You could use thispage to include or exclude parts of the sidebar based
on the page you include it in.  You can already use subpages/sidebar for
subpages/*, but thispage seems more flexible, makes it trivial to have
common portions rather than using [[plugins/inline]] with the raw
option, and keeps the sidebar in one place.


You could use thispage to implement multiple different feeds for the
same content with slightly different presentation.  For instance, using
templates for image inclusion, you could offer a feed with image links
and a feed with embedded images. Similarly, using templates for cuts, you
could offer a feed with cuts and a feed with full content in every post.


I don't have any particular attachment to sourcepage.  It only makes
sense as part of a template, since otherwise you know the source page when
typing in the if.
--[[JoshTriplett]]