This seemed to be due to the pagetemplate hook calling prerender. I've
observed this making it take *minutes* for the signin page to be displayed.
ltracing ikiwiki showed it was matching pagespecs a lot.
It may be that this is still a speed pain point when rendering pages, not
just for CGI. So more work may be needed here.
Since trail members are explicitly rebuilt if the information used for
their prev/up/next boxes changes, they don't need another dependency
on the trail itself. (If the trail disappears, it will disappear from
the member's member_to_trails entry, causing a rebuild; so the add_depends
is redundant.)
Similarly, since trail members are explicitly rebuilt if their next
or previous item, or its title, changes, the presence dependencies on the
next and previous items are redundant.
If the title of a trail changes, each member of that trail must be
rebuilt, for its prev/up/next box to reflect the new title.
If the title of a member changes, its next and previous items (if any)
must be rebuilt, for their prev/up/next boxes to reflect the new title.
In the unlikely event that the ordered contents of a trail have changed
without the TRAILS or TRAILLOOP template variables being evaluated
(for instance, all trail directives are removed from a former trail
that uses a custom pagetemplate that doesn't contain TRAILS), we might
get here without having already called prerender.
At some point I changed the storage of trail members' membership
and forgot to update this use.
(It turns out to be rather difficult to reach this code, possibly even
impossible: it only applies if a member somehow ceases to match the
trail's pagespec without either the trail or the member changing.)
Joey Hess
Simon McVittie