Polish KGP version checker (#1409)

*  Copy-pasted from https://github.com/vanniktech/gradle-maven-publish-plugin/blob/main/plugin/src/main/kotlin/com/vanniktech/maven/publish/MavenPublishBasePlugin.kt#L17-L41.

* Test for KMP 2.0.21-RC

* Rename

* Simplify `isAtLeastKgpVersion`

* Revert "Test for KMP 2.0.21-RC"

This reverts commit 5eecf0f.

* Revert "Simplify `isAtLeastKgpVersion`"

This reverts commit 595414e.

Author: Goooler

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

@@ -1,13 +1,13 @@
 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.isAtLeastKgpVersion
 import com.github.jengelman.gradle.plugins.shadow.internal.mainClassAttributeKey
 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
-import org.jetbrains.kotlin.gradle.dsl.KotlinVersion as KgpVersion
 import org.jetbrains.kotlin.gradle.targets.jvm.KotlinJvmTarget
 
 public abstract class ShadowKmpPlugin : Plugin<Project> {
@@ -30,7 +30,7 @@ public abstract class ShadowKmpPlugin : Plugin<Project> {
         },
       )
 
-      if (KgpVersion.DEFAULT < KgpVersion.KOTLIN_2_1) return@registerShadowJarCommon
+      if (!isAtLeastKgpVersion(2, 1, 0)) return@registerShadowJarCommon
 
       @OptIn(ExperimentalKotlinGradlePluginApi::class)
       target.mainRun {

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

@@ -1,5 +1,6 @@
 package com.github.jengelman.gradle.plugins.shadow
 
+import com.github.jengelman.gradle.plugins.shadow.internal.KOTLIN_MULTIPLATFORM_PLUGIN_ID
 import com.github.jengelman.gradle.plugins.shadow.legacy.LegacyShadowPlugin
 import org.gradle.api.Plugin
 import org.gradle.api.Project
@@ -18,7 +19,7 @@ public abstract class ShadowPlugin : Plugin<Project> {
     withType(ApplicationPlugin::class.java) {
       apply(ShadowApplicationPlugin::class.java)
     }
-    withId("org.jetbrains.kotlin.multiplatform") {
+    withId(KOTLIN_MULTIPLATFORM_PLUGIN_ID) {
       apply(ShadowKmpPlugin::class.java)
     }
 

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

@@ -0,0 +1,20 @@
+package com.github.jengelman.gradle.plugins.shadow.internal
+
+import org.gradle.api.Project
+import org.jetbrains.kotlin.gradle.plugin.KotlinBasePlugin
+
+internal const val KOTLIN_MULTIPLATFORM_PLUGIN_ID = "org.jetbrains.kotlin.multiplatform"
+
+internal fun Project.isAtLeastKgpVersion(
+  major: Int,
+  minor: Int,
+  patch: Int,
+  id: String = KOTLIN_MULTIPLATFORM_PLUGIN_ID,
+): Boolean {
+  val plugin = plugins.getPlugin(id) as KotlinBasePlugin
+  val elements = plugin.pluginVersion.takeWhile { it != '-' }.split(".")
+  val kgpMajor = elements[0].toInt()
+  val kgpMinor = elements[1].toInt()
+  val kgpPatch = elements[2].toInt()
+  return kgpMajor > major || (kgpMajor == major && (kgpMinor > minor || (kgpMinor == minor && kgpPatch >= patch)))
+}