extsearchidx: avoid needless alternates rewrite in ALL.git

As with fill_alternates in V2Writable, we do not need to update
$GIT_DIR/objects/info/alternates if nothing is changed.

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/PublicInbox/ExtSearchIdx.pm b/lib/PublicInbox/ExtSearchIdx.pm
index 9d576adb..9da42538 100644
--- a/lib/PublicInbox/ExtSearchIdx.pm
+++ b/lib/PublicInbox/ExtSearchIdx.pm
@@ -380,8 +380,11 @@ sub idx_init { # similar to V2Writable
                 $new{$line} = 1;
                 push @new, $line;
         }
-        push @old, @new;
-        PublicInbox::V2Writable::write_alternates($info_dir, $mode, \@old);
+        if (scalar @new) {
+                push @old, @new;
+                my $o = \@old;
+                PublicInbox::V2Writable::write_alternates($info_dir, $mode, $o);
+        }
         $self->parallel_init($self->{indexlevel});
         $self->umask_prepare;
         $self->with_umask(\&PublicInbox::V2Writable::_idx_init, $self, $opt);