manifest issue for shadow plugin with gradle - gradle

Question

I am using gradle v3.4 & shadow plugin v1.2.4. I am publishing a jar file to my local maven repo using the following inside my build.gradle file
mainClassName = 'some.thing.SomeClient'
jar {
manifest {
attributes(
'Class-Path': configurations.compile.collect { it.getName() }.join(' '),
// 'Main-Class': 'some.thing.SomeClient'
)
}
}
shadowJar {
baseName = 'commons-java'
classifier = null
version = '0.0.1-SNAPSHOT'
}
artifacts {
archives shadowJar
}
jar.dependsOn shadowJar
After publishing, I try to use this dependency inside another project as follows but get the error copied below when I run gradle build
/**
* jar/shadow jar (shadow jar extends jar task to create fat jar)
*/
jar {
manifest {
attributes(
'Class-Path': configurations.compile.collect { it.getName() }.join(' '),
//'Main-Class': 'some.thing.SomeClient'
)
}
}
shadowJar {
baseName = 'something-java-client'
classifier = null
version = '0.0.1-SNAPSHOT'
}
artifacts {
archives shadowJar
}
jar.dependsOn shadowJar
error
The value of a manifest attribute must not be null (Key=Main-Class).

Answer 1

The issue was caused by the mainClassName attribute in gradle.properties leading to the exception. Removing it from gradle.properties fixed the issue.

Answer 2

It also could be that the mainClassName is set after the plugin is applied, which seems to be a known issue. The quick and dirty solution is to set the property before applying the plugin, like this:
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.github.jengelman.gradle.plugins:shadow:2.0.2'
}
}
plugins {
id "application"
}
mainClassName = 'some.thing.SomeClient'
apply plugin: 'com.github.johnrengelman.shadow'
// ...