Why won't my Groovy main class execute from the built jar? - gradle

Question

I'm trying to build an executable JAR with a Groovy main class. I can get a Java main class to run exactly as expected, but the Groovy equivalent just isn't found and won't run.
In src/main/groovy/foo/Test.groovy:
package foo
public class Test { // (Yes, the public keywords here and below are redundant)
public static void main(String[] args) {
println "groovy world"
}
}
In src/main/groovy/foo/Test2.java:
package foo;
public class Test2 {
public static void main(String[] args) {
System.out.println("java world");
}
}
Gradle file:
plugins {
id 'java'
id 'groovy'
id 'application'
}
sourceCompatibility = 1.8
targetCompatibility = 1.8
mainClassName = 'foo.Test'
repositories {
mavenCentral()
}
dependencies {
compile group: 'org.codehaus.groovy', name: 'groovy-all', version: '2.4.7'
}
jar {
manifest {
attributes 'Main-Class': mainClassName
}
}
I build a JAR:
$ ./gradlew build
And try and run it (overriding the manifest Main-Class):
$ java -cp build/libs/test-groovy-main.jar foo.Test2
java world
$ java -cp build/libs/test-groovy-main.jar foo.Test
Error: Could not find or load main class foo.Test
If I turn on verbose output whilst doing this, in the second case I see "Loaded foo.Test2", but no "Loaded foo.Test" in the first.
I had thought that Groovy source compiles to plain java classes, and indeed decompiling the Test.class file I can see a public static main(String...) method in a public Test class. What am I doing wrong?
I'm using Gradle 2.6, Java 1.8.0 and Groovy 2.4.7 on Ubuntu 16.04.
I have the test case in version control here:
https://github.com/wu-lee/test-groovy-main

Answer 1

Adding of from section worked for me:
jar {
manifest {
attributes 'Main-Class': mainClassName
}
from {
configurations.compile.collect { it.isDirectory() ? it : zipTree(it) }
}
}
it puts the org.codehaus.groovy:groovy-all:2.4.7 dependency to your jar.
UPD
Created a pull-request https://github.com/wu-lee/test-groovy-main/pull/1