handle empty data directory in index check (#3981)

fixes #3980

Author: vladak

opengrok-indexer/src/main/java/org/opengrok/indexer/index/IndexCheck.java

@@ -18,7 +18,7 @@
  */
 
 /*
- * Copyright (c) 2018, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2022, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright (c) 2018, Chris Fraire <[email protected]>.
  */
 package org.opengrok.indexer.index;
@@ -28,6 +28,8 @@
 import java.util.Collection;
 import java.util.logging.Level;
 import java.util.logging.Logger;
+
+import org.apache.lucene.index.IndexNotFoundException;
 import org.apache.lucene.index.SegmentInfos;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.FSDirectory;
@@ -135,8 +137,13 @@ public static void checkDir(File dir) throws IndexVersionException, IOException
         int segVersion;
 
         try (Directory indexDirectory = FSDirectory.open(dir.toPath(), lockFactory)) {
-            SegmentInfos segInfos = SegmentInfos.readLatestCommit(indexDirectory);
-            segVersion = segInfos.getIndexCreatedVersionMajor();
+            try {
+                SegmentInfos segInfos = SegmentInfos.readLatestCommit(indexDirectory);
+                segVersion = segInfos.getIndexCreatedVersionMajor();
+            } catch (IndexNotFoundException e) {
+                LOGGER.log(Level.FINE, "no index found in ''{0}''", indexDirectory);
+                return;
+            }
         }
 
         if (segVersion != Version.LATEST.major) {

opengrok-indexer/src/test/java/org/opengrok/indexer/index/IndexCheckTest.java

@@ -18,7 +18,7 @@
  */
 
 /*
- * Copyright (c) 2018, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2022, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright (c) 2019, Chris Fraire <[email protected]>.
  */
 package org.opengrok.indexer.index;
@@ -33,6 +33,7 @@
 import java.util.Arrays;
 import java.util.List;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -42,6 +43,7 @@
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 import org.opengrok.indexer.configuration.Configuration;
 import org.opengrok.indexer.configuration.RuntimeEnvironment;
 import org.opengrok.indexer.history.RepositoryFactory;
@@ -140,4 +142,10 @@ void testIndexVersionOldIndex() throws Exception {
 
         assertThrows(IndexCheck.IndexVersionException.class, () -> IndexCheck.checkDir(indexDir));
     }
+
+    @Test
+    void testEmptyDir(@TempDir Path tempDir) throws Exception {
+        assertEquals(0, tempDir.toFile().list().length);
+        IndexCheck.checkDir(tempDir.toFile());
+    }
 }