Misleading error message when vaadin-maven-plugin is missing for npm modules

When migrating from V11 to V14 and running in npm mode, I got the following error message

Caused by: java.lang.IllegalStateException: Couldn't find the definition of the element with tag 'root-layout' in any template file declared using '@JsModule' annotations. Check the availability of the template files in your WAR file or provide alternative implementation of the method getTemplateContent() which should return an element representing the content of the template file

This occurred even when the root-layout.js had been created, and imported with @JsModule('src/root-layout.js');.

The reason turned out to be that this plugin and config was missing from the pom

<plugin>
    <groupId>com.vaadin</groupId>
    <artifactId>vaadin-maven-plugin</artifactId>
    <version>${vaadin.version}</version>
    <executions>
        <execution>
            <goals>
                <goal>validate</goal>
                <goal>build-frontend</goal>
            </goals>
        </execution>
    </executions>
</plugin>

The error message could be improved to detect when this whole part of the build process is missing.

Versions

Platform 14.0.0.alpha3 npm 6.9.0 node v11.9.0 vaadin-spring-boot-starter 14.0.0.alpha3

[pleku]

Manual migration will get some instructions later on, but the plan is to create a migration tool during platform beta which will handle for instance this case #5037

[denis-anisimov]

This should not be valid anymore: we have moved the logic from maven plugin to the server init phase meaning that if the plugin has not been executed then it will be done by the server itself. You have to make sure only that you are running NPM mode.

So :

• verify that this can be reproduced with the latest snapshot
• close the ticket if it can’t be reproduced or add more details about the current behavior if it’s still valid