K2 kapt: add kapt.use.k2 Gradle property

... and `-Kapt-use-k2` CLI flag to enable K2 kapt.

 #KT-61114 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kapt3IT.kt

@@ -121,6 +121,10 @@ open class Kapt3ClassLoadersCacheIT : Kapt3IT() {
     override fun testMultipleProcessingPasses(gradleVersion: GradleVersion) {
     }
 
+    @Disabled("classloaders cache is leaking file descriptors that prevents cleaning test project")
+    override fun useK2KaptProperty(gradleVersion: GradleVersion) {
+    }
+
     override fun testAnnotationProcessorAsFqName(gradleVersion: GradleVersion) {
         project("annotationProcessorAsFqName".withPrefix, gradleVersion) {
             //classloaders caching is not compatible with includeCompileClasspath
@@ -1268,6 +1272,41 @@ open class Kapt3IT : Kapt3BaseIT() {
         }
     }
 
+    @DisplayName("K2 Kapt can be enabled via Gradle property kapt.use.k2")
+    @GradleTest
+    open fun useK2KaptProperty(gradleVersion: GradleVersion) {
+        project("simple".withPrefix, gradleVersion) {
+            buildGradle.appendText(
+                """
+                |tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
+                |    compilerOptions {
+                |        freeCompilerArgs.addAll([
+                |            "-Xuse-fir-ic",
+                |            "-Xuse-fir-lt"
+                |        ])
+                |    }
+                |    kotlinOptions {
+                |        languageVersion = "2.0"
+                |    }
+                |}
+                |
+                |compileKotlin.kotlinOptions.allWarningsAsErrors = false
+                """.trimMargin()
+            )
+            build("-Pkapt.use.k2=true", "build") {
+                assertKaptSuccessful()
+                assertTasksExecuted(":kaptGenerateStubsKotlin", ":kaptKotlin", ":compileKotlin")
+                assertOutputDoesNotContain("Falling back to 1.9.")
+                assertOutputContains("Kapt 4 is an experimental feature. Use with caution.")
+            }
+            build("-Pkapt.use.k2=true", "cleanCompileKotlin", "compileKotlin") {
+                assertTasksExecuted(":compileKotlin")
+                // The warning should not be displayed for the compile task.
+                assertOutputDoesNotContain("Kapt 4 is an experimental feature. Use with caution.")
+            }
+        }
+    }
+
     @DisplayName("Kapt-generated Kotlin sources can be used in Kotlin")
     @GradleTest
     open fun useGeneratedKotlinSource(gradleVersion: GradleVersion) {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kapt4IT.kt

@@ -36,6 +36,9 @@ class Kapt4IT : Kapt3IT() {
     @Disabled("Doesn't make sense in Kapt 4")
     override fun fallBackModeWithLanguageVersion2_0(gradleVersion: GradleVersion) {}
 
+    @Disabled("Doesn't make sense in Kapt 4")
+    override fun useK2KaptProperty(gradleVersion: GradleVersion) {}
+
     @Disabled("Doesn't make sense in Kapt 4")
     override fun testRepeatableAnnotationsWithOldJvmBackend(gradleVersion: GradleVersion) {}
 

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

@@ -25,6 +25,7 @@ import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.isInf
 import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.isKaptKeepKdocCommentsInStubs
 import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.isKaptVerbose
 import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.isUseJvmIr
+import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.isUseK2
 import org.jetbrains.kotlin.gradle.model.builder.KaptModelBuilder
 import org.jetbrains.kotlin.gradle.plugin.*
 import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinJvmAndroidCompilation
@@ -109,6 +110,10 @@ class Kapt3GradleSubplugin @Inject internal constructor(private val registry: To
             return getBooleanOptionValue(BooleanOption.KAPT_USE_JVM_IR)
         }
 
+        fun Project.isUseK2(): Boolean {
+            return getBooleanOptionValue(BooleanOption.KAPT_USE_K2)
+        }
+
         fun Project.classLoadersCacheSize(): Int = findPropertySafe(CLASSLOADERS_CACHE_SIZE)?.toString()?.toInt() ?: 0
 
         fun Project.disableClassloaderCacheForProcessors(): Set<String> {
@@ -203,6 +208,7 @@ class Kapt3GradleSubplugin @Inject internal constructor(private val registry: To
             KAPT_INCLUDE_COMPILE_CLASSPATH("kapt.include.compile.classpath", true),
             KAPT_KEEP_KDOC_COMMENTS_IN_STUBS("kapt.keep.kdoc.comments.in.stubs", true),
             KAPT_USE_JVM_IR("kapt.use.jvm.ir", true),
+            KAPT_USE_K2("kapt.use.k2", false),
         }
     }
 
@@ -546,6 +552,7 @@ internal fun buildKaptSubpluginOptions(
     pluginOptions += SubpluginOption("showProcessorTimings", "${kaptExtension.showProcessorStats}")
     pluginOptions += SubpluginOption("detectMemoryLeaks", kaptExtension.detectMemoryLeaks)
     pluginOptions += SubpluginOption("useJvmIr", "${project.isUseJvmIr()}")
+    pluginOptions += SubpluginOption("useK2", "${project.isUseK2()}")
     pluginOptions += SubpluginOption("infoAsWarnings", "${project.isInfoAsWarnings()}")
     pluginOptions += FilesSubpluginOption("stubs", kaptStubsDir)
 

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/internal/kapt/KaptGenerateStubsTask.kt

@@ -17,9 +17,10 @@
 package org.jetbrains.kotlin.gradle.internal
 
 import org.gradle.api.Project
-import org.gradle.api.file.*
-import org.gradle.api.model.ObjectFactory
 import org.gradle.api.file.ConfigurableFileCollection
+import org.gradle.api.file.DirectoryProperty
+import org.gradle.api.file.FileCollection
+import org.gradle.api.model.ObjectFactory
 import org.gradle.api.provider.Property
 import org.gradle.api.tasks.*
 import org.gradle.work.Incremental
@@ -65,6 +66,9 @@ abstract class KaptGenerateStubsTask @Inject constructor(
     @get:Input
     abstract val verbose: Property<Boolean>
 
+    @get:Input
+    abstract val useK2Kapt: Property<Boolean>
+
     /**
      * Changes in this additional sources will trigger stubs regeneration,
      * but the sources themselves will not be used to find kapt annotations and generate stubs.
@@ -125,6 +129,10 @@ abstract class KaptGenerateStubsTask @Inject constructor(
 
             args.verbose = verbose.get()
             args.destinationAsFile = destinationDirectory.get().asFile
+
+            if (useK2Kapt.get()) {
+                args.freeArgs += "-Xuse-kapt4"
+            }
         }
 
         pluginClasspath { args ->

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/tasks/configuration/KaptGenerateStubsConfig.kt

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.gradle.dsl.KotlinTopLevelExtension
 import org.jetbrains.kotlin.gradle.internal.*
 import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.KAPT_SUBPLUGIN_ID
 import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.isIncludeCompileClasspath
+import org.jetbrains.kotlin.gradle.internal.Kapt3GradleSubplugin.Companion.isUseK2
 import org.jetbrains.kotlin.gradle.plugin.KaptExtension
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilationInfo
@@ -49,6 +50,7 @@ internal class KaptGenerateStubsConfig : BaseKotlinCompileConfig<KaptGenerateStu
         configureTask { task ->
             task.verbose.set(KaptTask.queryKaptVerboseProperty(project))
             task.pluginOptions.add(buildOptions(kaptExtension, task))
+            task.useK2Kapt.value(project.isUseK2()).finalizeValueOnRead()
 
             if (!isIncludeCompileClasspath(kaptExtension)) {
                 task.onlyIf {