Tap: bugfix for desynchronized repos (#1336)

This fixes the issue that was getting repos into a "desynchronized"
state. I was accidentally using `r.Commit`, not realizing that it
created a new commit, not return the existing commit details. This would
cause us to store & compare incorrect, locally-generated revs rather
than the rev from the commit message and subsequently end up skipping
valid commits, thinking they were an old rev.

Resolves #1315

Author: dholms

cmd/tap/firehose.go

@@ -187,15 +187,15 @@ func (fp *FirehoseProcessor) validateCommitAndFilterOps(ctx context.Context, evt
 		}
 	}
 
-	repoCommit, err := r.Commit()
+	dataCid, err := r.MST.RootCID()
 	if err != nil {
 		return nil, err
 	}
 
 	commit := &Commit{
 		Did:     evt.Repo,
-		Rev:     repoCommit.Rev,
-		DataCid: repoCommit.Data.String(),
+		Rev:     evt.Rev,
+		DataCid: dataCid.String(),
 		Ops:     parsedOps,
 	}