Fix negative maxDepth in Jetty 12.1 fullScan hot-reload scanner

- Resolves IllegalArgumentException on startup by setting scan depth to Integer.MAX_VALUE (which represents unlimited depth in Jetty 12.1) instead of the invalid negative -1 value.
- Applies the fix to both EE8 and EE11 configurations to ensure both support scanning deeply nested directories.
- Added e2e test (DevAppServerFullScanTest) that verifies the server boots without exceptions and successfully reloads when a nested resource file (> 3 levels deep) changes.
- Verified that on the original code, the EE8 server crashes on startup, and the EE11 server fails to trigger reloads for changes nested deeper than 3 directory levels.

Author: ludoch

e2etests/devappservertests/src/test/java/com/google/appengine/tools/development/DevAppServerFullScanTest.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * 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
+ *
+ *     https://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.appengine.tools.development;
+
+import com.google.common.collect.ImmutableList;
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+@RunWith(Parameterized.class)
+public class DevAppServerFullScanTest extends DevAppServerTestBase {
+
+  public DevAppServerFullScanTest(String runtimeVersion, String jettyVersion, String jakartaVersion) {
+    super(runtimeVersion, jettyVersion, jakartaVersion);
+  }
+
+  private File appDir;
+
+  @Before
+  public void setUpClass() throws IOException, InterruptedException {
+    appDir =
+        Boolean.getBoolean("appengine.use.EE10") || Boolean.getBoolean("appengine.use.EE11")
+            ? createApp("allinone_jakarta")
+            : createApp("allinone");
+    setUpClass(appDir);
+  }
+
+  @Override
+  protected List<String> getExtraJvmArgs() {
+    return ImmutableList.of("-Dappengine.fullscan.seconds=1");
+  }
+
+  @Test
+  public void testFullScanStartAndReload() throws Exception {
+    // Basic request to ensure server is running and hot reload scanner starts up fine
+    executeHttpGet("/?memcache_loops=1&memcache_size=1", "Running memcache for 1 loops with value size 1\nCache hits: 1\nCache misses: 0\n", RESPONSE_200);
+
+    // Clear logs to ensure we only search for the subsequent reload event
+    serverLogs.clear();
+
+    // Touch web.xml to trigger a reload
+    File webXml = new File(appDir, "WEB-INF/web.xml");
+    com.google.common.truth.Truth.assertThat(webXml.exists()).isTrue();
+    long oldLastModified = webXml.lastModified();
+    long newTime = oldLastModified + 2000;
+    boolean modified = webXml.setLastModified(newTime);
+    com.google.common.truth.Truth.assertThat(modified).isTrue();
+
+    // Verify that the hot-reload scanner initiates a reload
+    boolean reloaded = awaitLogContains("A file has changed, reloading the web application.", 10);
+    com.google.common.truth.Truth.assertThat(reloaded).isTrue();
+
+    // Clear logs again to test a deeply nested resource file (depth > 3)
+    serverLogs.clear();
+
+    File nestedClassFile = new File(appDir, "WEB-INF/classes/allinone/deeper/package/test/Dummy.properties");
+    nestedClassFile.getParentFile().mkdirs();
+    java.nio.file.Files.write(nestedClassFile.toPath(), new byte[]{0, 1, 2, 3});
+
+    // Verify that the hot-reload scanner initiates a reload for the deeply nested resource file
+    boolean nestedReloaded = awaitLogContains("A file has changed, reloading the web application.", 10);
+    com.google.common.truth.Truth.assertThat(nestedReloaded).isTrue();
+  }
+}

e2etests/devappservertests/src/test/java/com/google/appengine/tools/development/DevAppServerTestBase.java

@@ -48,6 +48,7 @@ public abstract class DevAppServerTestBase {
   int jettyPort;
   private Process runtimeProc;
   private CountDownLatch serverStarted;
+  protected final List<String> serverLogs = java.util.Collections.synchronizedList(new ArrayList<>());
 
   static final int NUMBER_OF_RETRIES = 5;
 
@@ -177,6 +178,7 @@ public void setUpClass(File appDir) throws IOException, InterruptedException {
     runtimeArgs.add("-Dappengine.use.EE10=" + System.getProperty("appengine.use.EE10"));
     runtimeArgs.add("-Dappengine.use.EE11=" + System.getProperty("appengine.use.EE11"));
     runtimeArgs.add("-Dappengine.use.jetty121=" + System.getProperty("appengine.use.jetty121"));
+    runtimeArgs.addAll(getExtraJvmArgs());
     runtimeArgs.add("-cp");
     runtimeArgs.add(TOOLS_JAR);
     runtimeArgs.add("com.google.appengine.tools.development.DevAppServerMain");
@@ -185,10 +187,19 @@ public void setUpClass(File appDir) throws IOException, InterruptedException {
     runtimeArgs.add("--allow_remote_shutdown"); // Keep as used in Maven plugin
     runtimeArgs.add("--disable_update_check"); // Keep, as used in Maven plugin
 
+    runtimeArgs.addAll(getExtraAppArgs());
     runtimeArgs.add(appDir.toString());
     createRuntime(ImmutableList.copyOf(runtimeArgs), ImmutableMap.of(), jettyPort);
   }
 
+  protected List<String> getExtraJvmArgs() {
+    return ImmutableList.of();
+  }
+
+  protected List<String> getExtraAppArgs() {
+    return ImmutableList.of();
+  }
+
   void createRuntime(
       ImmutableList<String> runtimeArgs,
       ImmutableMap<String, String> extraEnvironmentEntries,
@@ -221,8 +232,8 @@ private Process launchRuntime(
     pb.environment().putAll(extraEnvironmentEntries);
     Process process = pb.start();
 
-    OutputPump outPump = new OutputPump(process.getInputStream(), serverStarted);
-    OutputPump errPump = new OutputPump(process.getErrorStream(), serverStarted);
+    OutputPump outPump = new OutputPump(process.getInputStream(), serverStarted, serverLogs);
+    OutputPump errPump = new OutputPump(process.getErrorStream(), serverStarted, serverLogs);
     new Thread(outPump).start();
     new Thread(errPump).start();
     if (!serverStarted.await(120, TimeUnit.SECONDS)) {
@@ -284,12 +295,28 @@ void executeHttpGetWithRetriesContains(
     assertThat(retCode).isEqualTo(expectedReturnCode);
   }
 
+  protected boolean awaitLogContains(String expected, int timeoutSeconds) throws InterruptedException {
+    for (int i = 0; i < timeoutSeconds * 10; i++) {
+      synchronized (serverLogs) {
+        for (String logLine : serverLogs) {
+          if (logLine.contains(expected)) {
+            return true;
+          }
+        }
+      }
+      Thread.sleep(100);
+    }
+    return false;
+  }
+
   private static class OutputPump implements Runnable {
     private final BufferedReader stream;
     private final CountDownLatch serverStarted;
+    private final List<String> serverLogs;
 
-    public OutputPump(InputStream instream, CountDownLatch serverStarted) {
+    public OutputPump(InputStream instream, CountDownLatch serverStarted, List<String> serverLogs) {
       this.serverStarted = serverStarted;
+      this.serverLogs = serverLogs;
       this.stream = new BufferedReader(new InputStreamReader(instream, UTF_8));
     }
 
@@ -299,6 +326,7 @@ public void run() {
       try {
         while ((line = stream.readLine()) != null) {
           System.out.println(line);
+          serverLogs.add(line);
           if (line.contains("INFO: Dev App Server is now running")) {
             serverStarted.countDown();
           }

runtime/local_jetty121/src/main/java/com/google/appengine/tools/development/jetty/JettyContainerService.java

@@ -513,7 +513,7 @@ private void fullWebAppScanner(int interval) throws IOException {
     scanner.setScanInterval(interval);
     scanner.setScanDirs(scanList);
     scanner.setReportExistingFilesOnStartup(false);
-    scanner.setScanDepth(-1); // -1 means unlimited depth.
+    scanner.setScanDepth(Integer.MAX_VALUE); // Integer.MAX_VALUE means unlimited depth.
 
     scanner.addListener(
         new Scanner.BulkListener() {

runtime/local_jetty121_ee11/src/main/java/com/google/appengine/tools/development/jetty/ee11/JettyContainerService.java

@@ -507,7 +507,7 @@ private void fullWebAppScanner(int interval) throws IOException {
     scanner.setScanInterval(interval);
     scanner.setScanDirs(scanList);
     scanner.setReportExistingFilesOnStartup(false);
-    scanner.setScanDepth(3);
+    scanner.setScanDepth(Integer.MAX_VALUE); // Integer.MAX_VALUE means unlimited depth.
 
     scanner.addListener(
         new Scanner.BulkListener() {