Set Main-Class attr for KMP 2.1.0 or above

docs/changes/README.md

@@ -7,6 +7,8 @@
 
 - Add Kotlin DSL examples in docs. ([#1306](https://github.com/GradleUp/shadow/pull/1306))
 - Support using type-safe dependency accessors in `ShadowJar.dependencies`. ([#1322](https://github.com/GradleUp/shadow/pull/1322))
+- Set `Main-Class` attr from `kotlin.jvm().mainRun.mainClass`. ([#1337](https://github.com/GradleUp/shadow/pull/1337))  
+  This is added from Kotlin 2.1.20, which is still experimental.
 
 **Changed**
 

src/functionalTest/kotlin/com/github/jengelman/gradle/plugins/shadow/KmpPluginTest.kt

@@ -1,7 +1,10 @@
 package com.github.jengelman.gradle.plugins.shadow
 
 import assertk.assertThat
+import assertk.assertions.isEqualTo
+import com.github.jengelman.gradle.plugins.shadow.internal.mainClassAttributeKey
 import com.github.jengelman.gradle.plugins.shadow.util.containsEntries
+import com.github.jengelman.gradle.plugins.shadow.util.getMainAttr
 import kotlin.io.path.appendText
 import kotlin.io.path.writeText
 import org.junit.jupiter.api.BeforeEach
@@ -21,11 +24,14 @@ class KmpPluginTest : BasePluginTest() {
 
   @Test
   fun compatKmpJvmTarget() {
-    val mainClass = writeClass(sourceSet = "jvmMain", isJava = false)
+    val mainClassName = "my.MainKt"
+    val mainClassPath = writeClass(sourceSet = "jvmMain", isJava = false)
     projectScriptPath.appendText(
       """
         kotlin {
-          jvm()
+          jvm().mainRun {
+            mainClass = '$mainClassName'
+          }
           sourceSets {
             commonMain {
               dependencies {
@@ -46,9 +52,10 @@ class KmpPluginTest : BasePluginTest() {
 
     assertThat(outputShadowJar).useAll {
       containsEntries(
-        mainClass,
+        mainClassPath,
         *entriesInAB,
       )
+      getMainAttr(mainClassAttributeKey).isEqualTo(mainClassName)
     }
   }
 }

src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/ShadowKmpPlugin.kt

@@ -1,15 +1,20 @@
 package com.github.jengelman.gradle.plugins.shadow
 
 import com.github.jengelman.gradle.plugins.shadow.ShadowJavaPlugin.Companion.registerShadowJarCommon
+import com.github.jengelman.gradle.plugins.shadow.internal.mainClassAttributeKey
+import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
+import kotlin.collections.contains
 import org.gradle.api.Plugin
 import org.gradle.api.Project
+import org.jetbrains.kotlin.gradle.ExperimentalKotlinGradlePluginApi
 import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformExtension
 
 public abstract class ShadowKmpPlugin : Plugin<Project> {
+  private lateinit var kmpExtension: KotlinMultiplatformExtension
 
   override fun apply(project: Project) {
     with(project) {
-      val kmpExtension = extensions.getByType(KotlinMultiplatformExtension::class.java)
+      kmpExtension = extensions.getByType(KotlinMultiplatformExtension::class.java)
       val kotlinJvmMain = kmpExtension.jvm().compilations.named("main")
       registerShadowJarCommon { task ->
         task.from(kotlinJvmMain.map { it.output.allOutputs })
@@ -18,6 +23,22 @@ public abstract class ShadowKmpPlugin : Plugin<Project> {
             listOf(configurations.getByName(kotlinJvmMain.get().runtimeDependencyConfigurationName))
           },
         )
+        configureMainClass(task)
+      }
+    }
+  }
+
+  private fun configureMainClass(task: ShadowJar) {
+    if (KotlinVersion.CURRENT < KotlinVersion(2, 10, 20)) return
+
+    @OptIn(ExperimentalKotlinGradlePluginApi::class)
+    kmpExtension.jvm().mainRun {
+      task.inputs.property("mainClassName", mainClass)
+      task.doFirst {
+        // Inject the attribute if it is not already present.
+        if (!task.manifest.attributes.contains(mainClassAttributeKey)) {
+          task.manifest.attributes[mainClassAttributeKey] = mainClass.get()
+        }
       }
     }
   }