import: rewrite less history during purge

We do not need to rewrite old commits unaffected by the object_id
purge, only newer commits.  This was a state management bug :x

We will also return the new commit ID of rewritten history to
aid in incremental indexing of mirrors for the next change.

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/PublicInbox/V2Writable.pm b/lib/PublicInbox/V2Writable.pm
index 479e2b5d..b6532ac5 100644
--- a/lib/PublicInbox/V2Writable.pm
+++ b/lib/PublicInbox/V2Writable.pm
@@ -224,11 +224,13 @@ sub purge_oids {
         my ($self, $purge) = @_; # $purge = { $object_id => 1, ... }
         $self->done;
         my $pfx = "$self->{-inbox}->{mainrepo}/git";
+        my $purges = [];
         foreach my $i (0..$self->{max_git}) {
                 my $git = PublicInbox::Git->new("$pfx/$i.git");
                 my $im = $self->import_init($git, 0);
-                $im->purge_oids($purge);
+                $purges->[$i] = $im->purge_oids($purge);
         }
+        $purges;
 }
 
 sub remove_internal {
@@ -285,7 +287,7 @@ sub remove_internal {
                 $self->barrier;
         }
         if ($purge && scalar keys %$purge) {
-                purge_oids($self, $purge);
+                return purge_oids($self, $purge);
         }
         $removed;
 }