Help with 'Cannot change dependencies' error

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1

I’m trying to add the following to my build.gradle file:

 jar {
     manifest {
         attributes["Main-Class"] = "${mainClassName}"
         attributes["Class-Path"] = configurations.runtimeClasspath.collect { 'lib/' + it.getName() }.join(' ')
     }
 }

but when I try to build, I get this:

> Failed to notify project evaluation listener.
   > Cannot change dependencies of dependency configuration ':implementation' after it has been included in dependency resolution.
   > Cannot change dependencies of dependency configuration ':implementation' after it has been included in dependency resolution.

The problem seems to be directly related to this line:

        attributes["Class-Path"] = configurations.runtimeClasspath.collect { 'lib/' + it.getName() }.join(' ')

I stripped down my build.gradle file to just the following and I still get the error:

plugins {
    id("io.micronaut.application") version "3.3.2"
}

repositories {
    mavenCentral()
}

def pathInfo = configurations.runtimeClasspath.collect { 'lib/' + it.getName() }.join(' ')
logger.info('pathInfo {}', "${pathInfo}")

I’m fairly new to Gradle, so I’m trying to understand how iterating over the classpath and assigning the result to a variable should have something to do with changing the dependency configuration. There definitely seems to be something with using the Micronaut plugin, but since I don’t fully understand the error, I’m not sure what the real problem might be.

Looking for any insights that anyone might have on this. I’m running Gradle 7.4.2 on Ubuntu 20.04

2

What’s happening is that the runtimeClasspath configuration is being resolved during Gradle’s evalutation/configuration phase. Once this happens the configuration can no longer be mutated by the build/plugins. In order to defer the resolution of the configuration to Gradle’s task execution phase, update your buildscript to configure the manifest like so:

jar {
    doFirst {
        manifest {
            attributes["Main-Class"] = "${mainClassName}"
            attributes["Class-Path"] = configurations.runtimeClasspath.collect { 'lib/' + it.getName() }.join(' ')
        }
    }
}

When the jar task executes it will first configure the manifest attributes and then it will proceed with the creation of the jar.

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