If the title of a trail or trail-member changes, rebuild affected pages

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.

IkiWiki/Plugin/trail.pm

@@ -62,12 +62,20 @@ sub getsetup () {
 		},
 }
 
+# Cache of pages' old titles, so we can tell whether they changed
+my %old_trail_titles;
+
 sub needsbuild (@) {
 	my $needsbuild=shift;
+
 	foreach my $page (keys %pagestate) {
 		if (exists $pagestate{$page}{trail}) {
 			if (exists $pagesources{$page} &&
 			    grep { $_ eq $pagesources{$page} } @$needsbuild) {
+				# Remember its title, so we can know whether
+				# it changed.
+				$old_trail_titles{$page} = title_of($page);
+
 				# Remove state, it will be re-added
 				# if the preprocessor directive is still
 				# there during the rebuild. {item} is the
@@ -78,6 +86,7 @@ sub needsbuild (@) {
 			}
 		}
 	}
+
 	return $needsbuild;
 }
 
@@ -230,6 +239,12 @@ sub trails_differ {
 		if (! exists $new->{$trail}) {
 			return 1;
 		}
+
+		if (exists $old_trail_titles{$trail} &&
+			title_of($trail) ne $old_trail_titles{$trail}) {
+			return 1;
+		}
+
 		my ($old_p, $old_n) = @{$old->{$trail}};
 		my ($new_p, $new_n) = @{$new->{$trail}};
 		$old_p = "" unless defined $old_p;
@@ -239,9 +254,20 @@ sub trails_differ {
 		if ($old_p ne $new_p) {
 			return 1;
 		}
+
+		if (exists $old_trail_titles{$old_p} &&
+			title_of($old_p) ne $old_trail_titles{$old_p}) {
+			return 1;
+		}
+
 		if ($old_n ne $new_n) {
 			return 1;
 		}
+
+		if (exists $old_trail_titles{$old_n} &&
+			title_of($old_n) ne $old_trail_titles{$old_n}) {
+			return 1;
+		}
 	}
 
 	foreach my $trail (keys %$new) {

t/trail.t

@@ -275,21 +275,15 @@ check_trail("limited/c.html", "n=limited/d p=limited/b");
 check_trail("limited/d.html", "n= p=limited/c");
 # Also, b and d should pick up the change to c. This regressed with the
 # change to using a presence dependency.
-TODO: {
-local $TODO = "trail members don't pick up other members' title changes";
 $blob = readfile("t/tmp/out/limited/b.html");
 ok($blob =~ /New C page >/m);
 $blob = readfile("t/tmp/out/limited/d.html");
 ok($blob =~ /< New C page/m);
-}
 
 # Members of a retitled trail should pick up that change.
 # This regressed with the change to using a presence dependency.
-TODO: {
-local $TODO = "trail members don't pick up the trail's title changes";
 $blob = readfile("t/tmp/out/retitled/a.html");
 ok($blob =~ /\^ the new title \^/m);
-}
 
 # untrail is no longer a trail, so these are no longer in it.
 check_no_trail("untrail/a.html");