Align PackStatistics and DfsPackDescription list length

Without this the caller cannot tell which PackStatistics is for which
pack file.

Change-Id: Ifa530f8bc82459611ae694c0a0d111daec3e08f3
Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java

@@ -486,7 +486,12 @@ public class DfsGarbageCollector {
 		return newPackDesc;
 	}
 
-	/** @return statistics corresponding to the {@link #getNewPacks()}. */
+	/**
+	 * @return statistics corresponding to the {@link #getNewPacks()}.
+	 *
+	 * <p>The elements can be null if the stat is not available for the pack
+	 * file.
+	 */
 	public List<PackStatistics> getNewPackStatistics() {
 		return newPackStats;
 	}
@@ -637,7 +642,6 @@ public class DfsGarbageCollector {
 			ProgressMonitor pm, long estimatedPackSize) throws IOException {
 		DfsPackDescription pack = repo.getObjectDatabase().newPack(source,
 				estimatedPackSize);
-		newPackDesc.add(pack);
 
 		if (source == GC && reftableConfig != null) {
 			writeReftable(pack);
@@ -671,6 +675,7 @@ public class DfsGarbageCollector {
 		PackStatistics stats = pw.getStatistics();
 		pack.setPackStats(stats);
 		pack.setLastModified(startTimeMillis);
+		newPackDesc.add(pack);
 		newPackStats.add(stats);
 		newPackObj.add(pw.getObjectSet());
 		return pack;
@@ -680,6 +685,7 @@ public class DfsGarbageCollector {
 		if (reftableConfig != null) {
 			DfsPackDescription pack = objdb.newPack(GC);
 			newPackDesc.add(pack);
+			newPackStats.add(null);
 			writeReftable(pack);
 		}
 	}

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackCompactor.java

@@ -350,9 +350,13 @@ public class DfsPackCompactor {
 				: Collections.emptyList();
 	}
 
-	/** @return statistics corresponding to the {@link #getNewPacks()}. */
+	/**
+	 * @return statistics corresponding to the {@link #getNewPacks()}.
+	 *
+	 * <p>The element may be null if the stat is not available.
+	 */
 	public List<PackStatistics> getNewPackStatistics() {
-		return newStats != null
+		return outDesc != null
 				? Collections.singletonList(newStats)
 				: Collections.emptyList();
 	}