trail: call prerender from build_affected

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.

1 files changed, 6 insertions, 0 deletions

diff --git a/IkiWiki/Plugin/trail.pm b/IkiWiki/Plugin/trail.pm
index cf0f0a15e..86c94642a 100644
--- a/IkiWiki/Plugin/trail.pm
+++ b/IkiWiki/Plugin/trail.pm
@@ -359,6 +359,12 @@ sub prerender {
 sub build_affected {
 	my %affected;
 
+	# In principle we might not have done this yet, although in practice
+	# at least the trail itself has probably changed, and its template
+	# almost certainly contains TRAILS or TRAILLOOP, triggering our
+	# prerender as a side-effect.
+	prerender();
+
 	foreach my $member (keys %rebuild_trail_members) {
 		$affected{$member} = sprintf(gettext("building %s, its previous or next page has changed"), $member);
 	}