Grails with Vaadin 8 - 'Failed to load the widgetset" - grails

Question

I am a newbie in the areas in Grails and Vaadin 8, and I’m having a bit of trouble trying to add widgets to my Vaadin/Grails application.
To begin, I created a grails/Vaadin app using the me.przepiora.vaadin-grails:web-vaadin8:0.3 profile. I edited the build.gradel file, as advised and
ran the command ”gradle wrapper --gradle-version 4.0” (again, as advised by the profile setup).
Here is my build.gradle after applying the edit:
apply plugin:"com.devsoap.plugin.vaadin"
buildscript {
repositories {
mavenLocal()
maven { url "https://repo.grails.org/grails/core" }
maven { url "https://dl.bintray.com/macprzepiora/gradle-plugins/" }
}
dependencies {
classpath "org.grails:grails-gradle-plugin:$grailsVersion"
classpath "org.grails.plugins:hibernate5:${gormVersion-".RELEASE"}"
classpath "com.devsoap.plugin:gradle-vaadin-plugin:1.2.0.beta1-macprzepiora2"
classpath "com.bertramlabs.plugins:asset-pipeline-gradle:2.14.8"
}
}
version "0.1"
group "foobar"
apply plugin:"eclipse"
apply plugin:"idea"
apply plugin:"war"
apply plugin:"org.grails.grails-web"
apply plugin:"asset-pipeline"
apply plugin:"org.grails.grails-gsp"
repositories {
mavenLocal()
maven { url "https://repo.grails.org/grails/core" }
}
dependencies {
compile "org.springframework.boot:spring-boot-starter-logging"
compile "org.springframework.boot:spring-boot-autoconfigure"
compile "org.grails:grails-core"
compile "org.springframework.boot:spring-boot-starter-actuator"
compile "org.springframework.boot:spring-boot-starter-tomcat"
compile "org.grails:grails-web-boot"
compile "org.grails:grails-logging"
compile "org.grails:grails-plugin-rest"
compile "org.grails:grails-plugin-databinding"
compile "org.grails:grails-plugin-i18n"
compile "org.grails:grails-plugin-services"
compile "org.grails:grails-plugin-url-mappings"
compile "org.grails:grails-plugin-interceptors"
compile "org.grails.plugins:cache"
compile "org.grails.plugins:async"
compile "org.grails.plugins:scaffolding"
compile "com.vaadin:vaadin-spring-boot-starter:2.+"
compile "org.grails.plugins:events"
compile "org.grails.plugins:hibernate5"
compile "org.hibernate:hibernate-core:5.1.5.Final"
compile "org.grails.plugins:gsp"
console "org.grails:grails-console"
profile "me.przepiora.vaadin-grails:web-vaadin8:0.3"
runtime "org.glassfish.web:el-impl:2.1.2-b03"
runtime "com.h2database:h2"
runtime "org.apache.tomcat:tomcat-jdbc"
runtime "com.bertramlabs.plugins:asset-pipeline-grails:2.14.8"
testCompile "org.grails:grails-gorm-testing-support"
testCompile "org.grails:grails-web-testing-support"
}
bootRun {
jvmArgs('-Dspring.output.ansi.enabled=always')
addResources = true
String springProfilesActive = 'spring.profiles.active'
systemProperty springProfilesActive, System.getProperty(springProfilesActive)
}
plugins {
id 'com.devsoap.plugin.vaadin' version '1.3.1'
}
assets {
minifyJs = true
minifyCss = true
}
The resulting grails/Vaadin app worked fine, displaying a button which , when pressed, displayed an error message.
I then tried to enhance the app slightly, by replacing the button with a Vaadin Tree, backup by a TreeData instance.
Unfortunately, when I did this, I got the error message:
“Widgetset 'com.vaadin.DefaultWidgetSet' does not contain implementation for com.vaadin.ui.Tree Check its component connector's #Connect mapping, widgetsets GWT module description file and re-compile your widgetset. In case you have downloaded a vaadin add-on package, you might want to refer to add-on instructions.”
After a google search I found something that appeared to be related at:
How do I fix 'com.vaadin.DefaultWidgetSet' does not contain implementation for com.vaadin.addon.charts.Chart
Based on this, I added the line #Widgetset("AppWidgetset") to my GrailsUI class (the only class in my project that inherits from com.vaadin.ui.UI).
After doing this, I get a new runtime error:
“Failed to load the widgetset: ./VAADIN/widgetsets/AppWidgetset/AppWidgetset.nocache.js?1525623851485”
I feel so frustrated - it feels like i’m really close to a working application, if only I knew the magi incantation :-(