Gradle Application Plugin Main Class Not Recognized

Description of the issue: I’m using the Gradle application plugin and setting the main class for that:

application {
    mainClassName = "WebAppKt"
}

But the jib plugin is not picking up that setting:

com.google.cloud.tools.jib.plugins.common.MainClassInferenceException: Main class was not found, perhaps you should add a `mainClass` configuration to jib

Expected behavior: The main class should be picked up for jib if set for the application plugin.

Steps to reproduce: Create a build.gradle.kts with:

plugins {
    java
    application
    kotlin("jvm") version "1.3.20"
    id("kotlinx-serialization") version "1.3.20"
    id("com.google.cloud.tools.jib") version "1.0.0"
    id("com.github.johnrengelman.shadow") version "4.0.4"
}

repositories {
    mavenLocal()
    mavenCentral()
    maven("https://kotlin.bintray.com/kotlinx")
}

dependencies {
    compile("io.ktor:ktor-server-core:1.1.3")
    compile("io.ktor:ktor-server-netty:1.1.3")
    compile("io.ktor:ktor-freemarker:1.1.3")
    compile("io.ktor:ktor-client-cio:1.1.3")
    compile("io.ktor:ktor-client-json-jvm:1.1.3")
    compile("ch.qos.logback:logback-classic:1.2.3")
}

java {
    sourceCompatibility = JavaVersion.VERSION_1_8
}

tasks.compileKotlin {
    kotlinOptions.jvmTarget = "1.8"
}

application {
    mainClassName = "WebAppKt"
}

jib {
    val projectId: String? by project
    to.image = "gcr.io/$projectId/where-am-i"
}

Run with the latest gradle.

Environment: Linux

[chanseokoh]

Hi @jamesward,

IIRC, Jib is not able to automatically infer a main class in Kotlin (but I need to double-check that). I’m sure setting it explicitly will work.

jib {
  ...
  container.mainClass = "WebAppKt"
}

That said, we should understand why we cannot infer it for Kotlin.

[chanseokoh]

The auto-detection is fixed in 1.0.1 (by #1457), and #1503 is opened for reusing the application plugin’s settings. I’ll close this issue.