SOLR-18303: Stop backup cleanup from hiding the original failure

changelog/unreleased/SOLR-18303-incremental-backup-cleanup-masks-error.yml

@@ -0,0 +1,8 @@
+# See https://github.com/apache/solr/blob/main/dev-docs/changelog.adoc
+title: Incremental backup failures now report the original error instead of an unrelated missing zk_backup directory exception
+type: fixed
+authors:
+  - name: Prithvi S
+links:
+  - name: SOLR-18303
+    url: https://issues.apache.org/jira/browse/SOLR-18303

solr/core/src/java/org/apache/solr/cloud/api/collections/BackupCmd.java

@@ -133,8 +133,16 @@ public void call(AdminCmdContext adminCmdContext, ZkNodeProps message, NamedList
                     "Error happened during incremental backup for collection: {}",
                     collectionName,
                     e);
-                CollectionHandlingUtils.cleanBackup(
-                    repository, backupUri, backupMgr.getBackupId(), ccc);
+                try {
+                  CollectionHandlingUtils.cleanBackup(
+                      repository, backupUri, backupMgr.getBackupId(), ccc);
+                } catch (Exception cleanupException) {
+                  log.warn(
+                      "Unable to clean up incomplete backup for collection: {}",
+                      collectionName,
+                      cleanupException);
+                  e.addSuppressed(cleanupException);
+                }
                 throw e;
               }
             } else {

solr/core/src/java/org/apache/solr/cloud/api/collections/DeleteBackupCmd.java

@@ -25,6 +25,7 @@
 import java.io.IOException;
 import java.lang.invoke.MethodHandles;
 import java.net.URI;
+import java.nio.file.NoSuchFileException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -206,13 +207,14 @@ void deleteBackupIds(
             .map(ShardBackupId::getBackupMetadataFilename)
             .collect(Collectors.toList()));
     repository.delete(incBackupFiles.getIndexDir(), unusedFiles);
-    try {
-      for (BackupId backupId : backupIdsDeletes) {
-        repository.deleteDirectory(
-            repository.resolveDirectory(backupUri, BackupFilePaths.getZkStateDir(backupId)));
+    for (BackupId backupId : backupIdsDeletes) {
+      URI zkStateDir =
+          repository.resolveDirectory(backupUri, BackupFilePaths.getZkStateDir(backupId));
+      try {
+        repository.deleteDirectory(zkStateDir);
+      } catch (FileNotFoundException | NoSuchFileException e) {
+        // zk_backup_* is created after shard copy, so a failed incremental backup may not have it
       }
-    } catch (FileNotFoundException e) {
-      // ignore this
     }
 
     // add details to result before deleting backupPropFiles

solr/core/src/test/org/apache/solr/cloud/api/collections/DeleteBackupCmdTest.java

@@ -0,0 +1,92 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.cloud.api.collections;
+
+import java.io.IOException;
+import java.net.URI;
+import java.util.Set;
+import java.util.UUID;
+import org.apache.solr.SolrTestCase;
+import org.apache.solr.common.util.NamedList;
+import org.apache.solr.core.backup.BackupFilePaths;
+import org.apache.solr.core.backup.BackupId;
+import org.apache.solr.core.backup.repository.BackupRepository;
+import org.apache.solr.core.backup.repository.LocalFileSystemRepository;
+import org.junit.Before;
+import org.junit.Test;
+
+/** Unit tests for {@link DeleteBackupCmd}. */
+public class DeleteBackupCmdTest extends SolrTestCase {
+
+  private BackupRepository repository;
+  private URI backupUri;
+
+  @Before
+  public void setUpRepo() throws Exception {
+    repository = new LocalFileSystemRepository();
+    backupUri =
+        repository.createDirectoryURI(
+            createTempDir("backup_" + UUID.randomUUID()).toAbsolutePath().toString());
+    new BackupFilePaths(repository, backupUri).createIncrementalBackupFolders();
+  }
+
+  @Test
+  public void testDeleteBackupIdsIgnoresMissingZkStateDir() throws Exception {
+    NamedList<Object> results = new NamedList<>();
+    new DeleteBackupCmd(null)
+        .deleteBackupIds(backupUri, repository, Set.of(BackupId.zero()), results);
+
+    assertNotNull(results.get("deleted"));
+    assertFalse(repository.exists(zkStateDir(BackupId.zero())));
+  }
+
+  @Test
+  public void testDeleteBackupIdsRemovesExistingZkStateDir() throws Exception {
+    URI zkStateDir = zkStateDir(BackupId.zero());
+    repository.createDirectory(zkStateDir);
+    assertTrue(repository.exists(zkStateDir));
+
+    new DeleteBackupCmd(null)
+        .deleteBackupIds(backupUri, repository, Set.of(BackupId.zero()), new NamedList<>());
+
+    assertFalse(repository.exists(zkStateDir));
+  }
+
+  @Test
+  public void testDeleteBackupIdsPropagatesUnexpectedDeleteErrors() {
+    BackupRepository failingRepository =
+        new LocalFileSystemRepository() {
+          @Override
+          public void deleteDirectory(URI path) throws IOException {
+            throw new IOException("simulated repository failure");
+          }
+        };
+
+    IOException thrown =
+        expectThrows(
+            IOException.class,
+            () ->
+                new DeleteBackupCmd(null)
+                    .deleteBackupIds(
+                        backupUri, failingRepository, Set.of(BackupId.zero()), new NamedList<>()));
+    assertEquals("simulated repository failure", thrown.getMessage());
+  }
+
+  private URI zkStateDir(BackupId backupId) {
+    return repository.resolveDirectory(backupUri, BackupFilePaths.getZkStateDir(backupId));
+  }
+}