preserve datastore-indexes-auto across non-clean rebuilds

src/main/java/com/google/cloud/tools/gradle/appengine/standard/ExplodeWarTask.java

@@ -18,15 +18,36 @@
 package com.google.cloud.tools.gradle.appengine.standard;
 
 import java.io.File;
+import org.gradle.api.Action;
 import org.gradle.api.tasks.Sync;
+import org.gradle.api.tasks.util.PatternFilterable;
 
 /** Expand a war. */
 public class ExplodeWarTask extends Sync {
+
+  private File explodedAppDirectory;
+
   public void setWarFile(File warFile) {
     from(getProject().zipTree(warFile));
   }
 
+  /**
+   * Sets the output directory of Sync Task and preserves the setting so it can be recovered later
+   * via getter.
+   */
   public void setExplodedAppDirectory(File explodedAppDirectory) {
+    this.explodedAppDirectory = explodedAppDirectory;
     into(explodedAppDirectory);
+    preserve(
+        new Action<PatternFilterable>() {
+          @Override
+          public void execute(PatternFilterable patternFilterable) {
+            patternFilterable.include("WEB-INF/appengine-generated/datastore-indexes-auto.xml");
+          }
+        });
+  }
+
+  public File getExplodedAppDirectory() {
+    return explodedAppDirectory;
   }
 }

src/test/java/com/google/cloud/tools/gradle/appengine/standard/ExplodeWarTaskTest.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2017 Google Inc. All Right Reserved.
+ *
+ * Licensed 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 com.google.cloud.tools.gradle.appengine.standard;
+
+import com.google.cloud.tools.gradle.appengine.TestProject;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import org.gradle.testkit.runner.BuildResult;
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+public class ExplodeWarTaskTest {
+
+  @Rule public final TemporaryFolder testProjectDir = new TemporaryFolder();
+
+  @Test
+  public void testSyncTask() throws IOException {
+    BuildResult buildResult =
+        new TestProject(testProjectDir.getRoot())
+            .addStandardBuildFile()
+            .addAppEngineWebXml()
+            .applyGradleRunner("explodeWar");
+
+    Path explodedApp =
+        testProjectDir
+            .getRoot()
+            .toPath()
+            .resolve("build")
+            .resolve("exploded-" + testProjectDir.getRoot().getName());
+    Path appengineGenerated = explodedApp.resolve("WEB-INF").resolve("appengine-generated");
+    Path junkXml = appengineGenerated.resolve("junk.xml");
+    Path datastoreIndexesAutoXml = appengineGenerated.resolve("datastore-indexes-auto.xml");
+
+    Assert.assertTrue(Files.isDirectory(explodedApp));
+    Assert.assertFalse(Files.isRegularFile(datastoreIndexesAutoXml));
+    Assert.assertFalse(Files.isRegularFile(junkXml));
+
+    // creates files that we will test persistence on
+    Files.createDirectory(appengineGenerated);
+    Files.createFile(junkXml);
+    Files.createFile(datastoreIndexesAutoXml);
+
+    // run explodeWar again to see if we preserve datastore-indexes-auto and remove junk, force
+    // it to skip UP-TO-DATE checks
+    new TestProject(testProjectDir.getRoot()).applyGradleRunner("explodeWar", "--rerun-tasks");
+
+    Assert.assertTrue(Files.isRegularFile(datastoreIndexesAutoXml));
+    Assert.assertFalse(Files.isRegularFile(junkXml));
+  }
+}