Local dev server fails to start

[zdenda]

Starting the local development server (DevAppServer / Gradle appengineStart) fails with exception:

com.google.appengine.tools.development.jetty.JettyContainerService startHotDeployScanner
INFO: Full scan of the web app in place every 1s.
java.lang.RuntimeException: java.lang.IllegalArgumentException: 'maxDepth' is negative
	at org.eclipse.jetty.util.component.LifeCycle.start(LifeCycle.java:59)
	at com.google.appengine.tools.development.jetty.JettyContainerService.fullWebAppScanner(JettyContainerService.java:527)
	at com.google.appengine.tools.development.jetty.JettyContainerService.startHotDeployScanner(JettyContainerService.java:429)
	at com.google.appengine.tools.development.AbstractContainerService.startup(AbstractContainerService.java:286)
	at com.google.appengine.tools.development.AutomaticInstanceHolder.startUp(AutomaticInstanceHolder.java:42)
	at com.google.appengine.tools.development.AbstractModule.startup(AbstractModule.java:101)
	at com.google.appengine.tools.development.Modules.startup(Modules.java:133)
	at com.google.appengine.tools.development.DevAppServerImpl.doStart(DevAppServerImpl.java:275)
	at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:228)
	at com.google.appengine.tools.development.DevAppServerMain$StartAction.apply(DevAppServerMain.java:383)
	at com.google.appengine.tools.util.Parser$ParseResult.applyArgs(Parser.java:58)
	at com.google.appengine.tools.development.DevAppServerMain.run(DevAppServerMain.java:239)
	at com.google.appengine.tools.development.DevAppServerMain.main(DevAppServerMain.java:230)
Caused by: java.lang.IllegalArgumentException: 'maxDepth' is negative
	at java.base/java.nio.file.FileTreeWalker.<init>(FileTreeWalker.java:188)
	at java.base/java.nio.file.Files.walkFileTree(Files.java:2791)
	at org.eclipse.jetty.util.Scanner.scanFiles(Scanner.java:832)
	at org.eclipse.jetty.util.Scanner.startScanning(Scanner.java:711)
	at org.eclipse.jetty.util.Scanner.doStart(Scanner.java:678)
	at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:92)
	at org.eclipse.jetty.util.component.LifeCycle.start(LifeCycle.java:55)
	... 12 more
Caused by: java.lang.IllegalArgumentException: 'maxDepth' is negative

Environment

• Google Cloud SDK: 572.0.0 (Last working SDK: 568.0.0)
• Runtime: java17
• Build tool: com.google.cloud.tools.appengine-appenginewebxml Gradle plugin, appengineStart
• OS: Windows 11

AI Analysis of this issue (Take this with a grain of salt, but it might help)

Introduced by: fcc24ef#diff-6451d30fd34f0beafb3ec7f80d2acc7ffa27f634727bb7ce71a4437cf7cf4623R516

Summary

Starting the local development server (DevAppServer / Gradle appengineStart) fails immediately when full-scan hot-reload is active, because JettyContainerService.fullWebAppScanner(int) calls scanner.setScanDepth(-1). Jetty 12.1's Scanner passes that value straight to Files.walkFileTree(...), which throws IllegalArgumentException: 'maxDepth' is negative. The comment // -1 means unlimited depth. reflects an old Jetty 9 API contract that no longer holds for the Jetty 12.1 Scanner.

Root cause

runtime/local_jetty121/.../jetty/JettyContainerService.java (current main, line 516):

scanner.setScanDepth(-1); // -1 means unlimited depth.

Jetty's Scanner.scanFiles() (Scanner.java:832) does:

Files.walkFileTree(root, options, _scanDepth, visitor);

and Files.walkFileTree mandates maxDepth >= 0, throwing IllegalArgumentException otherwise. Jetty's Scanner has used the native walkFileTree(maxDepth) form for a long time (the file is byte-identical between jetty-12.1.8 and jetty-12.1.10), so -1 was never valid on Jetty 12.1 — only the older Jetty 9 Scanner tolerated it as "unlimited".

Regression origin

Introduced by commit fcc24ef (2026-05-06):

"Modified JettyContainerService.java to set the file scanner depth to unlimited (-1) in the local development server. This was an ancient regression after removing Jetty9 where the API was different."

It changed setScanDepth(3) → setScanDepth(-1). Verified via bytecode of the shipped runtime jars:

• SDK 568 JettyContainerService.fullWebAppScanner: iconst_3 → setScanDepth(3) (works)
• SDK 572 JettyContainerService.fullWebAppScanner: iconst_m1 → setScanDepth(-1) (throws)

Note the EE11 variant (local_jetty121_ee11/.../JettyContainerService.java) correctly uses setScanDepth(3); only the EE8 local_jetty121 path regressed.

Suggested fix

Use a valid non-negative depth. Jetty's documented "unlimited" value is Integer.MAX_VALUE:

scanner.setScanDepth(Integer.MAX_VALUE); // unlimited; Jetty 12.1 Scanner rejects negative depth

(or restore the previous 3, matching the EE11 runtime). Either keeps deep WEB-INF rescans working without violating Jetty's walkFileTree contract.

[ludoch]

looking.

[ludoch]

Fix will be publish next Tuesday in the new Cloud CLI.

[zdenda]

Thank you. I can confirm that the issue has been fixed and that my local development server is working with Google Cloud SDK 573.0.0 (app-engine-java 5.0.4).