thoughts on some future stuff

doc/todo/optimisations.mdwn

@@ -2,9 +2,21 @@
   times in worst case (8 times if there's an rss feed).
 
   The issue is that rendering a page is used to gather info like the links
-  on the page that can effect rendering other pages. So it needs a
-  multi-pass system. But rendering the whole page in each pass is rather
-  obscene.
+  on the page (and other stuff) that can effect rendering other pages. So it
+  needs a multi-pass system. But rendering the whole page in each pass is
+  rather obscene.
+  
+  It would be better to have the first pass be a data gathering pass. Such
+  a pass would still need to load and parse the page contents etc, but
+  wouldn't need to generate html or write anything to disk.
+
+  One problem with this idea is that it could turn into 2x the work in
+  cases where ikiwiki currently efficiently renders a page just once. And
+  caching between the passes to avoid that wouldn't do good things to the
+  memory footprint.
+
+  Might be best to just do a partial first pass, getting eg, the page links
+  up-to-date, and then multiple, but generally fewer, rendering passes.
 
 * Don't render blog archive pages unless a page is added/removed. Just
   changing a page doesn't affect the archives as they show only the title.

doc/todo/plugin_dependency_calulation.mdwn

@@ -0,0 +1,23 @@
+A few plugins need more complex dependency calculations than ikiwiki can do
+on its own:
+
+* Use of a version plugin should only make the page rebuild when it's built
+  with a new version of ikiwiki.
+* The [[plugins/sidebar]] plugin should make any page get rebuilt if a
+  sidebar is created "closer" to it than the current sidebar.
+* Some plugin might want to _always_ rebuild the page that uses it.
+* If backlinks were turned into a plugin, it would need to make a page
+  rebuild when its backlinks changed.
+
+These suggest there should be a way for plugins to have hooks that tweak
+the list of pages to rebuild.
+
+Which in turn suggests that there should *be* a list of pages to rebuild;
+currently there's not, and the best such an interface could do would be to
+rebuild the pages even if they were already going to be rebuilt for some
+other reason. (See [[optimisation]].)
+
+It also suggests that plugins will want to examine pages and/or
+[[store_data|plugin_data_storage]] about them to use in the dependency
+calculations. For example, the version plugin would need to store info
+about what pages use it.