search: improve reindexing behavior

For reindexing, fresh Xapian DBs do not count as a reindex,
allowing users to blindly use --reindex on the first
run on a clean repo.

While we're at it, allow indexing to override HEAD ref for
multi-head git repos.

1 files changed, 12 insertions, 6 deletions

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 6a34ce71..f0a3687d 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -374,7 +374,7 @@ sub rlog {
 # indexes all unindexed messages
 sub _index_sync {
         my ($self, $opts) = @_;
-        my $head = 'HEAD';
+        my $tip = $opts->{ref} || 'HEAD';
         my $mm = $self->{mm} = eval {
                 require PublicInbox::Msgmap;
                 PublicInbox::Msgmap->new($self->{git_dir}, 1);
@@ -382,8 +382,13 @@ sub _index_sync {
         my $xdb = $self->{xdb};
         $xdb->begin_transaction;
         my $reindex = $opts->{reindex};
-        my $mkey = $reindex ? undef : 'last_commit';
-        my $lx = $reindex ? '' : $xdb->get_metadata('last_commit');
+        my $mkey = 'last_commit';
+        my $last_commit = $xdb->get_metadata($mkey);
+        my $lx = $last_commit;
+        if ($reindex) {
+                $lx = '';
+                $mkey = undef if $last_commit ne '';
+        }
         my $dbh;
         my $cb = sub {
                 my ($commit, $more) = @_;
@@ -398,7 +403,7 @@ sub _index_sync {
                 $xdb = _xdb_acquire($self);
         };
 
-        my $range = $lx eq '' ? $head : "$lx..$head";
+        my $range = $lx eq '' ? $tip : "$lx..$tip";
         if ($mm) {
                 $dbh = $mm->{dbh};
                 $dbh->begin_work;
@@ -413,14 +418,15 @@ sub _index_sync {
                         # This happens if we have to reindex Xapian since
                         # msgmap is a frozen format and our Xapian format
                         # is evolving.
-                        my $r = $lm eq '' ? $head : "$lm..$head";
+                        my $r = $lm eq '' ? $tip : "$lm..$tip";
 
                         # first, ensure msgmap is up-to-date:
+                        my $mkey_prev = $mkey;
                         $mkey = undef; # ignore xapian, for now
                         rlog($self, $r, *index_mm, *unindex_mm, $cb);
 
                         # now deal with Xapian
-                        $mkey = 'last_commit' unless $reindex;
+                        $mkey = $mkey_prev;
                         $dbh = undef;
                         rlog($self, $range, *index_mm2, *unindex_mm2, $cb);
                 }