Deprecate 1.2.x MPP Gradle plugins

Issue #KT-31570 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/MultiplatformGradleIT.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.gradle
 
 import com.intellij.testFramework.TestDataPath
+import org.jetbrains.kotlin.gradle.internals.KOTLIN_12X_MPP_DEPRECATION_WARNING
 import org.jetbrains.kotlin.gradle.plugin.EXPECTED_BY_CONFIG_NAME
 import org.jetbrains.kotlin.gradle.plugin.IMPLEMENT_CONFIG_NAME
 import org.jetbrains.kotlin.gradle.plugin.IMPLEMENT_DEPRECATION_WARNING
@@ -35,6 +36,9 @@ class MultiplatformGradleIT : BaseGradleIT() {
 
         project.build("build") {
             assertSuccessful()
+
+            assertContains(KOTLIN_12X_MPP_DEPRECATION_WARNING)
+
             assertTasksExecuted(
                 ":lib:compileKotlinCommon",
                 ":lib:compileTestKotlinCommon",
@@ -50,6 +54,13 @@ class MultiplatformGradleIT : BaseGradleIT() {
             assertFileExists("libJs/build/classes/kotlin/main/libJs.js")
             assertFileExists("libJs/build/classes/kotlin/test/libJs_test.js")
         }
+
+        project.projectDir.resolve("gradle.properties").appendText("\nkotlin.internal.mpp12x.deprecation.suppress=true")
+        project.build {
+            assertSuccessful()
+
+            assertNotContains(KOTLIN_12X_MPP_DEPRECATION_WARNING)
+        }
     }
 
     @Test

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinMultiplatformPlugin.kt

@@ -26,6 +26,7 @@ import org.gradle.api.tasks.SourceSet
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
 import org.jetbrains.kotlin.gradle.logging.kotlinWarn
 import org.jetbrains.kotlin.gradle.tasks.AbstractKotlinCompile
+import org.jetbrains.kotlin.gradle.utils.SingleWarningPerBuild
 
 abstract class KotlinPlatformPluginBase(protected val platformName: String) : Plugin<Project> {
     companion object {
@@ -38,6 +39,7 @@ abstract class KotlinPlatformPluginBase(protected val platformName: String) : Pl
 
 open class KotlinPlatformCommonPlugin : KotlinPlatformPluginBase("common") {
     override fun apply(project: Project) {
+        warnAboutKotlin12xMppDeprecation(project)
         project.applyPlugin<KotlinCommonPluginWrapper>()
     }
 }
@@ -55,6 +57,8 @@ open class KotlinPlatformImplementationPluginBase(platformName: String) : Kotlin
         listOf(project.configurations.getByName("compile"))
 
     override fun apply(project: Project) {
+        warnAboutKotlin12xMppDeprecation(project)
+
         val implementConfig = project.configurations.create(IMPLEMENT_CONFIG_NAME)
         val expectedByConfig = project.configurations.create(EXPECTED_BY_CONFIG_NAME)
 
@@ -245,3 +249,17 @@ open class KotlinPlatformJsPlugin : KotlinPlatformImplementationPluginBase("js")
         super.apply(project)
     }
 }
+
+internal val KOTLIN_12X_MPP_DEPRECATION_WARNING = "\n" + """
+    The 'org.jetbrains.kotlin.platform.*' plugins are deprecated and will no longer be available in Kotlin 1.4.
+    Please migrate the project to the 'org.jetbrains.kotlin.multiplatform' plugin.
+    See: https://kotlinlang.org/docs/reference/building-mpp-with-gradle.html
+    """.trimIndent()
+
+private const val KOTLIN_12X_MPP_DEPRECATION_SUPPRESS_FLAG = "kotlin.internal.mpp12x.deprecation.suppress"
+
+private fun warnAboutKotlin12xMppDeprecation(project: Project) {
+    if (project.findProperty(KOTLIN_12X_MPP_DEPRECATION_SUPPRESS_FLAG) != "true") {
+        SingleWarningPerBuild.show(project, KOTLIN_12X_MPP_DEPRECATION_WARNING)
+    }
+}

libraries/tools/kotlin-gradle-plugin/src/test/kotlin/org/jetbrains/kotlin/gradle/internals/ExposedForIntegrationTests.kt

@@ -27,4 +27,6 @@ const val DISABLED_NATIVE_TARGETS_REPORTER_WARNING_PREFIX: String =
     DisabledNativeTargetsReporter.WARNING_PREFIX
 
 const val NO_NATIVE_STDLIB_WARNING = NO_NATIVE_STDLIB_WARNING
-const val NO_NATIVE_STDLIB_PROPERTY_WARNING = NO_NATIVE_STDLIB_PROPERTY_WARNING
+const val NO_NATIVE_STDLIB_PROPERTY_WARNING = NO_NATIVE_STDLIB_PROPERTY_WARNING
+
+val KOTLIN_12X_MPP_DEPRECATION_WARNING = org.jetbrains.kotlin.gradle.plugin.KOTLIN_12X_MPP_DEPRECATION_WARNING