PatchListCache: Add method for getting old ID of a patch set

For a batch NoteDb rebuilding job with its own PatchListCache
implementation, this method is much easier to implement than the more
generic get methods. Plus, it simplifies the code in setCommentRevId.

Change-Id: Iee126283e04328f2a497d99efe0f4f9cdc961590

gerrit-server/src/main/java/com/google/gerrit/server/PatchLineCommentsUtil.java

@@ -41,7 +41,6 @@ import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.notedb.ChangeUpdate;
 import com.google.gerrit.server.notedb.DraftCommentNotes;
 import com.google.gerrit.server.notedb.NotesMigration;
-import com.google.gerrit.server.patch.PatchList;
 import com.google.gerrit.server.patch.PatchListCache;
 import com.google.gerrit.server.patch.PatchListNotAvailableException;
 import com.google.gwtorm.server.OrmException;
@@ -363,14 +362,9 @@ public class PatchLineCommentsUtil {
         "cannot set RevId for patch set %s on comment %s", ps.getId(), c);
     if (c.getRevId() == null) {
       try {
-        if (Side.fromShort(c.getSide()) == Side.REVISION) {
+        c.setRevId(Side.fromShort(c.getSide()) == Side.PARENT
-          c.setRevId(ps.getRevision());
+            ? new RevId(ObjectId.toString(cache.getOldId(change, ps)))
-        } else {
+            : ps.getRevision());
-          PatchList patchList = cache.get(change, ps);
-          c.setRevId((c.getSide() == (short) 0)
-            ? new RevId(ObjectId.toString(patchList.getOldId()))
-            : new RevId(ObjectId.toString(patchList.getNewId())));
-        }
       } catch (PatchListNotAvailableException e) {
         throw new OrmException(e);
       }

gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListCache.java

@@ -18,6 +18,8 @@ import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gerrit.reviewdb.client.Project;
 
+import org.eclipse.jgit.lib.ObjectId;
+
 /** Provides a cached list of {@link PatchListEntry}. */
 public interface PatchListCache {
   PatchList get(PatchListKey key, Project.NameKey project)
@@ -26,6 +28,9 @@ public interface PatchListCache {
   PatchList get(Change change, PatchSet patchSet)
       throws PatchListNotAvailableException;
 
+  ObjectId getOldId(Change change, PatchSet patchSet)
+      throws PatchListNotAvailableException;
+
   IntraLineDiff getIntraLineDiff(IntraLineDiffKey key,
       IntraLineDiffArgs args);
 }

gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListCacheImpl.java

@@ -106,6 +106,12 @@ public class PatchListCacheImpl implements PatchListCache {
     return get(new PatchListKey(null, b, ws), project);
   }
 
+  @Override
+  public ObjectId getOldId(Change change, PatchSet patchSet)
+      throws PatchListNotAvailableException {
+    return get(change, patchSet).getOldId();
+  }
+
   @Override
   public IntraLineDiff getIntraLineDiff(IntraLineDiffKey key,
       IntraLineDiffArgs args) {