+
+----
+
+I implemented the above in a branch.
+[[!template id=gitbranch branch=origin/dependency-types author="[[joey]]"]]
+
+Then I found some problems:
+
+* Something simple like pagecount, that seems like it could use a
+ contentless dependency, can have a pagespec that uses metadata, like
+ `author()` or `copyright()`.
+* pagestats, orphans and brokenlinks cannot use contentless dependencies
+ because they need to update when links change.
+
+Now I'm thinking about having a contentless dependency look at page
+metadata, and fire if the metadata changes. And it seems links should
+either be included in that, or there should be a way to make a dependency
+that fires when a page's links change. (And what about backlinks?)
+
+It's easy to see when a page's links change, since there is `%oldlinks`.
+To see when metadata is changed is harder, since it's stored in the
+pagestate by the meta plugin.
+
+Quick alternative: Make add_depends look at the pagespec. Ie, if it
+is a simple page name, or a glob, we know a contentless dependency
+can be valid. If's more complex, convert the dependency from
+contentless to full.
+
+There is a lot to dislike about this method. Its parsing of the
+pagespec, as currently implemented, does not let plugins add new types of
+pagespecs that are contentless. Its pagespec parsing is also subject to
+false negatives (though these should be somewhat rare, and no false
+positives). Still, it does work, and it makes things like simple maps and
+pagecounts much more efficient.