Store: support empty stores in cleanupAndVerify (#116059)

Until now if `store.cleanupAndVerify` was called on a store with no
commits, it would throw `IndexNotFoundException`. Based on variable
naming (`metadataOrEmpty`), this appears to be unintentional, though the
issue has been present since the `cleanupAndVerify` method was
introduced.

This change is motivated by #104473 - I would like to be able to use
this method to clean up a store prior to recovery regardless of how
far along a previous recovery attempt got.

Author: bcully

server/src/main/java/org/elasticsearch/index/store/Store.java

@@ -696,7 +696,12 @@ public void cleanupAndVerify(String reason, MetadataSnapshot sourceMetadata) thr
                 }
             }
             directory.syncMetaData();
-            final Store.MetadataSnapshot metadataOrEmpty = getMetadata(null);
+            Store.MetadataSnapshot metadataOrEmpty;
+            try {
+                metadataOrEmpty = getMetadata(null);
+            } catch (IndexNotFoundException e) {
+                metadataOrEmpty = MetadataSnapshot.EMPTY;
+            }
             verifyAfterCleanup(sourceMetadata, metadataOrEmpty);
         } finally {
             metadataLock.writeLock().unlock();

server/src/test/java/org/elasticsearch/index/store/StoreTests.java

@@ -732,6 +732,15 @@ public void testCleanupFromSnapshot() throws IOException {
         IOUtils.close(store);
     }
 
+    public void testCleanupEmptyStore() throws IOException {
+        final ShardId shardId = new ShardId("index", "_na_", 1);
+        Store store = new Store(shardId, INDEX_SETTINGS, StoreTests.newDirectory(random()), new DummyShardLock(shardId));
+
+        store.cleanupAndVerify("test", Store.MetadataSnapshot.EMPTY);
+
+        IOUtils.close(store);
+    }
+
     public void testOnCloseCallback() throws IOException {
         final ShardId shardId = new ShardId(
             new Index(randomRealisticUnicodeOfCodepointLengthBetween(1, 10), "_na_"),