fix: copy backup issue when backup is done across different instance IDs

README.md

@@ -50,20 +50,20 @@ If you are using Maven without the BOM, add this to your dependencies:
 If you are using Gradle 5.x or later, add this to your dependencies:
 
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:26.25.0')
+implementation platform('com.google.cloud:libraries-bom:26.27.0')
 
 implementation 'com.google.cloud:google-cloud-spanner'
 ```
 If you are using Gradle without BOM, add this to your dependencies:
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-spanner:6.52.1'
+implementation 'com.google.cloud:google-cloud-spanner:6.53.0'
 ```
 
 If you are using SBT, add this to your dependencies:
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.52.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.53.0"
 ```
 <!-- {x-version-update-end} -->
 
@@ -432,7 +432,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-spanner/java11.html
 [stability-image]: https://img.shields.io/badge/stability-stable-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-spanner.svg
-[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.52.1
+[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.53.0
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication
 [auth-scopes]: https://developers.google.com/identity/protocols/oauth2/scopes
 [predefined-iam-roles]: https://cloud.google.com/iam/docs/understanding-roles#predefined_roles

google-cloud-spanner/src/main/java/com/google/cloud/spanner/BackupInfo.java

@@ -156,9 +156,6 @@ public Builder setVersionTime(Timestamp versionTime) {
 
     @Override
     public Builder setDatabase(DatabaseId database) {
-      Preconditions.checkArgument(
-          database.getInstanceId().equals(id.getInstanceId()),
-          "The instance of the source database must be equal to the instance of the backup.");
       this.database = Preconditions.checkNotNull(database);
       return this;
     }

google-cloud-spanner/src/test/java/com/google/cloud/spanner/DatabaseAdminClientImplTest.java

@@ -73,6 +73,7 @@
 public class DatabaseAdminClientImplTest {
   private static final String PROJECT_ID = "my-project";
   private static final String INSTANCE_ID = "my-instance";
+  private static final String INSTANCE_ID_2 = "my-instance-2";
   private static final String INSTANCE_NAME = "projects/my-project/instances/my-instance";
   private static final String DB_ID = "my-db";
   private static final String DB_NAME = "projects/my-project/instances/my-instance/databases/my-db";
@@ -591,6 +592,41 @@ public void copyBackupWithBackupObject() throws ExecutionException, InterruptedE
     assertThat(op.get().getId().getName()).isEqualTo(BK_NAME);
   }
 
+  @Test
+  public void copyBackupWithBackupObject_onDifferentInstances()
+      throws ExecutionException, InterruptedException {
+    Backup testProto =
+        Backup.newBuilder()
+            .setName(BK_NAME)
+            .setDatabase("projects/my-project/instances/my-instance-2/databases/my-db")
+            .setState(Backup.State.READY)
+            .build();
+    final OperationFuture<Backup, CopyBackupMetadata> rawOperationFuture =
+        OperationFutureUtil.immediateOperationFuture(
+            "copyBackup", testProto, CopyBackupMetadata.getDefaultInstance());
+    final Timestamp expireTime =
+        Timestamp.ofTimeMicroseconds(
+            TimeUnit.MILLISECONDS.toMicros(System.currentTimeMillis())
+                + TimeUnit.HOURS.toMicros(28));
+    final Timestamp versionTime =
+        Timestamp.ofTimeMicroseconds(
+            TimeUnit.MILLISECONDS.toMicros(System.currentTimeMillis()) - TimeUnit.DAYS.toMicros(2));
+    final com.google.cloud.spanner.Backup requestBackup =
+        client
+            .newBackupBuilder(BackupId.of(PROJECT_ID, INSTANCE_ID_2, BK_ID))
+            .setExpireTime(expireTime)
+            .setVersionTime(versionTime)
+            .build();
+    BackupId sourceBackupId = BackupId.of(PROJECT_ID, INSTANCE_ID, BK_ID);
+
+    when(rpc.copyBackup(sourceBackupId, requestBackup)).thenReturn(rawOperationFuture);
+
+    final OperationFuture<com.google.cloud.spanner.Backup, CopyBackupMetadata> op =
+        client.copyBackup(sourceBackupId, requestBackup);
+    assertThat(op.isDone()).isTrue();
+    assertThat(op.get().getId().getName()).isEqualTo(BK_NAME);
+  }
+
   @Test
   public void copyEncryptedBackup() throws ExecutionException, InterruptedException {
     final OperationFuture<Backup, CopyBackupMetadata> rawOperationFuture =