ClassNotFoundException when running TaskGenerateOpenAPI with flow-maven-plugin

[mshabarov]

Describe the bug

Due to the latest changes in Hilla endpoints discovery, the projects that use flow-maven-plugin and vaadin-spring-boot-starter (e.g. MPR + Spring projects) are failing with

Caused by: java.lang.ClassNotFoundException: org.springframework.boot.loader.tools.MainClassFinder
    at jdk.internal.loader.BuiltinClassLoader.loadClass (BuiltinClassLoader.java:641)
    at java.lang.ClassLoader.loadClass (ClassLoader.java:525)
    at com.vaadin.flow.plugin.maven.Reflector$CombinedClassLoader.loadClass (Reflector.java:392)
    at com.vaadin.hilla.engine.AotBrowserCallableFinder.determineApplicationClass (AotBrowserCallableFinder.java:59)
    at com.vaadin.hilla.engine.AotBrowserCallableFinder.findEndpointClasses (AotBrowserCallableFinder.java:36)
    at com.vaadin.hilla.engine.EngineConfiguration.lambda$getBrowserCallableFinder$1 (EngineConfiguration.java:130)
    at com.vaadin.hilla.internal.TaskGenerateOpenAPIImpl.execute (TaskGenerateOpenAPIImpl.java:64)
    at com.vaadin.flow.server.frontend.NodeTasks.execute (NodeTasks.java:347)
    at com.vaadin.flow.plugin.base.BuildFrontendUtil.runNodeUpdater (BuildFrontendUtil.java:364)
    at com.vaadin.flow.plugin.maven.BuildFrontendMojo.executeInternal (BuildFrontendMojo.java:143)

Note: MPR project uses flow-maven-plugin, because they need to also run the V8 vaadin-maven-plugin.

The problem happens if the project is using vaadin-spring-boot-starter.
When building for production the Hilla's TaskGenerateOpenAPIImpl is called and it fails because of java.lang.ClassNotFoundException: org.springframework.boot.loader.tools.MainClassFinder.

The easy fix is to exclude Hilla from a project, but it's a breaking change.

Expected-behavior

Project should not fail event though it's being build with flow-maven-plugin instead of vaadin-maven-plugin.

Reproduction

Can be reproduced with the MPR test module Session IT.

System Info

Vaadin 24.7.0.alpha7 or 24.7-SNAPSHOT.

[mcollovati]

Another workaround is to use hilla-maven-plugin instead of flow-maven-plugin