Gradle Kotlin DSL: could not find or load main class

$ ./gradlew --version                                                                                                    

------------------------------------------------------------
Gradle 7.1.1
------------------------------------------------------------

Build time:   2021-07-02 12:16:43 UTC
Revision:     774525a055494e0ece39f522ac7ad17498ce032c

Kotlin:       1.4.31
Groovy:       3.0.7
Ant:          Apache Ant(TM) version 1.10.9 compiled on September 27 2020
JVM:          11.0.11 (Amazon.com Inc. 11.0.11+9-LTS)
OS:           Mac OS X 11.4 x86_64

I have defined tasks.jar like so:

tasks.jar {
    manifest {
        attributes(mapOf("Main-Class" to mainClassName))
    }

    configurations["compileClasspath"].forEach { file: File ->
        from(zipTree(file.absoluteFile))
    }
}

I have other dependencies in the project that I would like to package into a fat jar.

When I run ./gradlew jar, the build succeeds but it cannot find the main class:

$ ./gradlew jar

BUILD SUCCESSFUL in 1s
2 actionable tasks: 2 executed

$ java -jar build/libs/myapp-0.0.1-SNAPSHOT.jar
Error: Could not find or load main class mypackage.Hello
Caused by: java.lang.ClassNotFoundException: mypackage.Hello

$ jar xf build/libs/myapp-0.0.1-SNAPSHOT.jar META-INF/MANIFEST.MF
$ cat META-INF/MANIFEST.MF
Manifest-Version: 1.0
Main-Class: mypackage.Hello

$ jar -tf build/libs/myapp-0.0.1-SNAPSHOT.jar | grep mypackage                                                          1
mypackage/
mypackage/Hello.class

If I remove this section:

    configurations["compileClasspath"].forEach { file: File ->
        from(zipTree(file.absoluteFile))
    }

then it can find the main class, but the other dependencies are no longer packaged into the fat jar.

$ java -jar build/libs/myapp-0.0.1-SNAPSHOT.jar
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/logging/log4j/LogManager
        at mypackage.Hello.<clinit>(Hello.java:8)
Caused by: java.lang.ClassNotFoundException: org.apache.logging.log4j.LogManager
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
        ... 1 more

Here is the full build.gradle.kts file:

group = "mypackage"
version = "0.0.1-SNAPSHOT"

java {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
    withSourcesJar()
}

plugins {
    `java-library`
}

repositories {
    mavenCentral()
    maven {
        url = uri("https://mvnrepository.com/artifact/com.microsoft.azure/azure-storage")
    }
}

dependencies {
    val azureStorageVersion = "12.12.0"
    val log4jCoreVersion = "2.14.1"
    val log4jSlf4jImplVersion = "2.14.1"

    implementation("com.azure:azure-storage-blob:$azureStorageVersion")
    implementation("org.apache.logging.log4j:log4j-core:$log4jCoreVersion")
    implementation("org.apache.logging.log4j:log4j-slf4j-impl:$log4jSlf4jImplVersion")

    val junitVersion = "5.7.1"
    testImplementation("org.junit.jupiter:junit-jupiter:$junitVersion")
}

val mainClassName = "mypackage.Hello"
tasks.jar {
    duplicatesStrategy = DuplicatesStrategy.INCLUDE
    manifest {
        attributes(mapOf("Main-Class" to mainClassName))
    }

    from(configurations.compileClasspath.get().map { if (it.isDirectory) it else zipTree(it) })
}

tasks.test {
    useJUnitPlatform()
}

Bumping this thread for help.

Adding sample project: GitHub - darkasphalt/myapp