Task copying frontend resources does not visit the full classpath (dev-mode 2.0.3)

[manolo]

Issue

• clone bookstore-starter-flow project
• update platform version to 14.0.0.rc5
• when in the root folder run mvn install -DskipTests
• move to the bookstore-starter-flow-ui and run mvn jetty:run
• you can see that web-pack-dev-server fails because it does not find connectors in node_modules/@vaadin/flow-frontend

Cause

TaskUpdatePackages cleans the node_modules folder because platform version changed, but TaskCopyFrontendFiles does not copies all the files since apparently the system property java.class.path does not include all the jars in the application classpath.

In my local only one jar was passed /usr/local/Cellar/maven/3.6.0/libexec/boot/plexus-classworlds-2.5.2.jar which obviously is not the classpath of the application. The servlet container does not set the system property appropriately, and we need to figure out the jars used in the app from the class loader

Workaround

run mvn prepare-package before running mvn jetty:run the first time. It needs to be run again after cleaning or changing dependencies

[caalador]

The question is why would you use maven without using the maven plugin?
The runtime copying is only for when the application is started from an ide that actually adds the dependencies to the property (maven doesn't do this).

I expect the problem is that the copyResources step is in BuildFrontend and not in PrepareFrontend

[Legioth]

#6083 will also be needed before this issue can be properly closed.