I'd like to see some way to include certain files from the underlay only when the wiki has certain plugins enabled. For example:
- Only include smileys.mdwn and the smileys subdirectory if you enable the smiley plugin.
- Exclude openid.mdwn if you disable the openid plugin.
- Include shortcuts.mdwn only if you enable the shortcut plugin.
- Include blog.mdwn only if you don't disable the inline plugin.
- Include favicon.ico only if you enable the favicon plugin.
- Include wikiicons/diff.png (and the wikiicons directory) only if you enable the CGI.
- Include a hypothetical restructuredtexthelp.rst or similar for other formats only with those formats enabled.
I can see two good ways to implement this. Ideally, with conditional text based on ikiwiki features available, ikiwiki could parse a page like conditionalpages.mdwn, which could contain a set of conditional-wrapped page names; that seems like the most elegant and ikiwiki-like approach. Alternatively, ikiwiki.setup could contain a Perl-generated exclude option by default; that would work, but it seems hackish.
Another way might be to have a third directory of source files where plugins could drop in pages, and only build the files from there if their plugins were enabled.
Using the conditionals in a page to control what other pages get built feels complex to me.