Fixup for the fix of KT-39809

In the original fix for KT-39809, the Kapt plugin was not given a proper
empty implementation stub: it was added to `Kapt3GradleSubplugin`, while
originally the Kapt subplugin's META-INF/services entry pointed to
`Kapt3KotlinGradleSubplugin`.

This commit makes the correct class implement the legacy interface.

Issue #KT-39809 Fixed

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

@@ -5,8 +5,10 @@
 
 package org.jetbrains.kotlin.gradle
 
+import org.jetbrains.kotlin.gradle.util.AGPVersion
 import org.jetbrains.kotlin.gradle.util.checkBytecodeContains
 import org.jetbrains.kotlin.gradle.util.modify
+import org.jetbrains.kotlin.test.KotlinTestUtils
 import org.junit.Test
 import java.io.File
 import kotlin.test.assertTrue
@@ -193,10 +195,10 @@ class SubpluginsIT : BaseGradleIT() {
     }
 
     @Test
-    fun testKotlinVersionDowngradeInSupbrojectKt39809() = with(Project("multiprojectWithDependency")) {
+    fun testKotlinVersionDowngradeInSupbrojectKt39809() = with(Project("android-dagger", directoryPrefix = "kapt2")) {
         setupWorkingDir()
 
-        projectDir.resolve("projA/build.gradle").modify {
+        gradleBuildScript("app").modify {
             """
                 buildscript {
                 	repositories {
@@ -210,7 +212,13 @@ class SubpluginsIT : BaseGradleIT() {
                 $it
             """.trimIndent()
         }
-        build(":projA:compileKotlin") {
+        build(
+            ":app:compileDebugKotlin",
+            options = defaultBuildOptions().copy(
+                androidGradlePluginVersion = AGPVersion.v3_4_1,
+                androidHome = KotlinTestUtils.findAndroidSdk()
+            )
+        ) {
             assertSuccessful()
         }
     }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/kapt/Kapt3KotlinGradleSubplugin.kt

@@ -43,9 +43,7 @@ import javax.inject.Inject
 
 // apply plugin: 'kotlin-kapt'
 class Kapt3GradleSubplugin @Inject internal constructor(private val registry: ToolingModelBuilderRegistry) :
-    KotlinCompilerPluginSupportPlugin,
+    KotlinCompilerPluginSupportPlugin {
-    @Suppress("DEPRECATION") // implementing to fix KT-39809
-    KotlinGradleSubplugin<AbstractCompile> {
 
     override fun apply(target: Project) {
         target.extensions.create("kapt", KaptExtension::class.java)
@@ -591,20 +589,6 @@ class Kapt3GradleSubplugin @Inject internal constructor(private val registry: To
 
     override fun getPluginArtifact(): SubpluginArtifact =
         JetBrainsSubpluginArtifact(artifactId = KAPT_ARTIFACT_NAME)
-
-    //region Stub implementation for legacy API, KT-39809
-    internal constructor(): this(object : ToolingModelBuilderRegistry {
-        override fun register(p0: ToolingModelBuilder) = Unit
-        override fun getBuilder(p0: String): ToolingModelBuilder? = null
-    })
-
-    override fun isApplicable(project: Project, task: AbstractCompile): Boolean = false
-
-    override fun apply(
-        project: Project, kotlinCompile: AbstractCompile, javaCompile: AbstractCompile?, variantData: Any?, androidProjectHandler: Any?,
-        kotlinCompilation: KotlinCompilation<KotlinCommonOptions>?
-    ): List<SubpluginOption> = emptyList()
-    //endregion
 }
 private val artifactType = Attribute.of("artifactType", String::class.java)
 
@@ -708,4 +692,20 @@ private val BaseVariant.dataBindingDependencyArtifactsIfSupported: FileCollectio
     get() = this::class.java.methods
         .find { it.name == "getDataBindingDependencyArtifacts" }
         ?.also { it.isAccessible = true }
-        ?.invoke(this) as? FileCollection
+        ?.invoke(this) as? FileCollection
+
+//region Stub implementation for legacy API, KT-39809
+@Suppress("DEPRECATION") // implementing to fix KT-39809
+class Kapt3KotlinGradleSubplugin : KotlinGradleSubplugin<AbstractCompile> {
+    override fun isApplicable(project: Project, task: AbstractCompile): Boolean = false
+
+    override fun apply(
+        project: Project, kotlinCompile: AbstractCompile, javaCompile: AbstractCompile?, variantData: Any?, androidProjectHandler: Any?,
+        kotlinCompilation: KotlinCompilation<KotlinCommonOptions>?
+    ): List<SubpluginOption> = emptyList()
+
+    override fun getCompilerPluginId(): String = Kapt3GradleSubplugin.KAPT_SUBPLUGIN_ID
+
+    override fun getPluginArtifact(): SubpluginArtifact = JetBrainsSubpluginArtifact(artifactId = Kapt3GradleSubplugin.KAPT_ARTIFACT_NAME)
+}
+//endregion