+# returns prefix => pathname mapping
+# (pathname is NOT public, but prefix is used for Xapian queries)
+sub altid_map ($) {
+ my ($self) = @_;
+ $self->{-altid_map} //= eval {
+ require PublicInbox::AltId;
+ my $altid = $self->{altid} or return {};
+ my %h = map {;
+ my $x = PublicInbox::AltId->new($self, $_);
+ "$x->{prefix}" => $x->{filename}
+ } @$altid;
+ \%h;
+ } // {};
+}
+