Upgrade to Kotlin 2.1.0

This commit upgrades to Kotlin 2.1.0. Two related dependencies have been
updated as well: Kotlin Coroutines to 1.10, and Kotlin Serialization to
1.8.

As of Kotlin 2, it is no longer possible to have a Java type and a
Kotlin type with the same name. As our code samples follow that
unfortunate pattern, this commit makes sure that the Kotlin sample code
does not depend on any of the Java counterpart and configure the kotlin
compilation plugin to ignore Java sources.

The minimum version of Gradle is 7.6.4. It bundles a version of Kotlin
that cannot compile a Kotlin build script when spring-core, compiled
with Kotlin 2.1, is on the classpath. Using Gradle 8.12 to run the DSL
tests avoids the problem.

Closes gh-45486

Co-authored-by: Andy Wilkinson <andy.wilkinson@broadcom.com>

.gitignore

@@ -41,3 +41,4 @@ secrets.yml
 .sts4-cache
 .git-hooks/
 node_modules
+/.kotlin/

buildSrc/build.gradle

@@ -42,7 +42,6 @@ dependencies {
 	implementation("org.apache.maven:maven-artifact:${mavenVersion}")
 	implementation("org.antora:gradle-antora-plugin:1.0.0")
 	implementation("org.jetbrains.kotlin:kotlin-gradle-plugin:${kotlinVersion}")
-	implementation("org.jetbrains.kotlin:kotlin-compiler-embeddable:${kotlinVersion}")
 	implementation("org.springframework:spring-context")
 	implementation("org.springframework:spring-core")
 	implementation("org.springframework:spring-web")

buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,15 +17,15 @@
 package org.springframework.boot.build;
 
 import java.net.URI;
-import java.util.ArrayList;
-import java.util.List;
 
 import dev.adamko.dokkatoo.DokkatooExtension;
 import dev.adamko.dokkatoo.formats.DokkatooHtmlPlugin;
 import org.gradle.api.Project;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.SourceSetContainer;
-import org.jetbrains.kotlin.gradle.dsl.KotlinJvmOptions;
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget;
+import org.jetbrains.kotlin.gradle.dsl.KotlinJvmCompilerOptions;
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion;
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile;
 
 /**
@@ -56,14 +56,12 @@ class KotlinConventions {
 	}
 
 	private void configure(KotlinCompile compile) {
-		KotlinJvmOptions kotlinOptions = compile.getKotlinOptions();
+		KotlinJvmCompilerOptions compilerOptions = compile.getCompilerOptions();
-		kotlinOptions.setApiVersion("1.7");
+		compilerOptions.getApiVersion().set(KotlinVersion.KOTLIN_2_1);
-		kotlinOptions.setLanguageVersion("1.7");
+		compilerOptions.getLanguageVersion().set(KotlinVersion.KOTLIN_2_1);
-		kotlinOptions.setJvmTarget("17");
+		compilerOptions.getJvmTarget().set(JvmTarget.JVM_17);
-		kotlinOptions.setAllWarningsAsErrors(true);
+		compilerOptions.getAllWarningsAsErrors().set(true);
-		List<String> freeCompilerArgs = new ArrayList<>(kotlinOptions.getFreeCompilerArgs());
+		compilerOptions.getFreeCompilerArgs().addAll("-Xsuppress-version-warnings");
-		freeCompilerArgs.add("-Xsuppress-version-warnings");
-		kotlinOptions.setFreeCompilerArgs(freeCompilerArgs);
 	}
 
 	private void configureDokkatoo(Project project) {

gradle.properties

@@ -14,7 +14,7 @@ hamcrestVersion=3.0
 jacksonVersion=2.18.4
 javaFormatVersion=0.0.43
 junitJupiterVersion=5.12.2
-kotlinVersion=1.9.25
+kotlinVersion=2.1.0
 mavenVersion=3.9.4
 mockitoVersion=5.17.0
 nativeBuildToolsVersion=0.10.6

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -1174,10 +1174,6 @@ bom {
 		}
 	}
 	library("Kotlin", "${kotlinVersion}") {
-		prohibit {
-			versionRange "[2.0.0-Beta1,)"
-			because "it exceeds our baseline"
-		}
 		group("org.jetbrains.kotlin") {
 			bom("kotlin-bom")
 			plugins = [
@@ -1190,11 +1186,7 @@ bom {
 			releaseNotes("https://github.com/JetBrains/kotlin/releases/tag/v{version}")
 		}
 	}
-	library("Kotlin Coroutines", "1.8.1") {
+	library("Kotlin Coroutines", "1.10.1") {
-		prohibit {
-			versionRange "[1.9.0-RC,)"
-			because "it requires Kotlin 2"
-		}
 		group("org.jetbrains.kotlinx") {
 			bom("kotlinx-coroutines-bom")
 		}
@@ -1203,11 +1195,7 @@ bom {
 			releaseNotes("https://github.com/Kotlin/kotlinx.coroutines/releases/tag/{version}")
 		}
 	}
-	library("Kotlin Serialization", "1.6.3") {
+	library("Kotlin Serialization", "1.8.0") {
-		prohibit {
-			versionRange "[1.7.0-RC,)"
-			because "it requires Kotlin 2"
-		}
 		group("org.jetbrains.kotlinx") {
 			bom("kotlinx-serialization-bom")
 		}

spring-boot-project/spring-boot-docs/build.gradle

@@ -1,3 +1,4 @@
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompilationTask
 import org.springframework.boot.build.docs.ConfigureJavadocLinks
 
 plugins {
@@ -46,6 +47,11 @@ sourcesJar {
 	enabled = false
 }
 
+// To avoid a redeclaration error with Kotlin compiler
+tasks.named('compileKotlin', KotlinCompilationTask.class) {
+    javaSources.from = []
+}
+
 plugins.withType(EclipsePlugin) {
 	eclipse.classpath { classpath ->
 		classpath.plusConfigurations.add(configurations.getByName(sourceSets.main.runtimeClasspathConfigurationName))

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/features/kotlin.adoc

@@ -15,7 +15,7 @@ Feel free to join the #spring channel of https://slack.kotlinlang.org/[Kotlin Sl
 [[features.kotlin.requirements]]
 == Requirements
 
-Spring Boot requires at least Kotlin 1.7.x and manages a suitable Kotlin version through dependency management.
+Spring Boot requires at least Kotlin 2.1.x and manages a suitable Kotlin version through dependency management.
 To use Kotlin, `org.jetbrains.kotlin:kotlin-stdlib` and `org.jetbrains.kotlin:kotlin-reflect` must be present on the classpath.
 The `kotlin-stdlib` variants `kotlin-stdlib-jdk7` and `kotlin-stdlib-jdk8` can also be used.
 

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/data/nosql/cassandra/connecting/User.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.data.nosql.cassandra.connecting
+
+class User

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/features/externalconfig/typesafeconfigurationproperties/usingannotatedtypes/Server.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.features.externalconfig.typesafeconfigurationproperties.usingannotatedtypes
+
+class Server(remoteAddress: Any?) {
+	fun start() {
+
+	}
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/features/springapplication/applicationavailability/managing/CacheCompletelyBrokenException.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.features.springapplication.applicationavailability.managing
+
+class CacheCompletelyBrokenException: RuntimeException()

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/features/testcontainers/atdevelopmenttime/importingcontainerdeclarations/MyContainers.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.features.testcontainers.atdevelopmenttime.importingcontainerdeclarations
+
+class MyContainers {
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/features/testcontainers/atdevelopmenttime/importingcontainerdeclarations/MyContainersConfiguration.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,6 @@
 
 package org.springframework.boot.docs.features.testcontainers.atdevelopmenttime.importingcontainerdeclarations
 
-import org.springframework.boot.docs.features.devservices.testcontainers.atdevelopmenttime.importingcontainerdeclarations.MyContainers
 import org.springframework.boot.test.context.TestConfiguration
 import org.springframework.boot.testcontainers.context.ImportTestcontainers
 

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/packaging/nativeimage/advanced/nestedconfigurationproperties/Nested.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.packaging.nativeimage.advanced.nestedconfigurationproperties
+
+class Nested {
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/using/springbeansanddependencyinjection/multipleconstructors/AccountService.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.using.springbeansanddependencyinjection.multipleconstructors
+
+interface AccountService {
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/using/springbeansanddependencyinjection/multipleconstructors/RiskAssessor.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.using.springbeansanddependencyinjection.multipleconstructors
+
+interface RiskAssessor {
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/using/springbeansanddependencyinjection/singleconstructor/AccountService.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.using.springbeansanddependencyinjection.singleconstructor
+
+interface AccountService {
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/using/springbeansanddependencyinjection/singleconstructor/RiskAssessor.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.using.springbeansanddependencyinjection.singleconstructor
+
+interface RiskAssessor {
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/using/usingthespringbootapplicationannotation/individualannotations/AnotherConfiguration.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.using.usingthespringbootapplicationannotation.individualannotations
+
+class AnotherConfiguration

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/using/usingthespringbootapplicationannotation/individualannotations/SomeConfiguration.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.using.usingthespringbootapplicationannotation.individualannotations
+
+class SomeConfiguration

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/web/servlet/springmvc/errorhandling/MyErrorBody.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.web.servlet.springmvc.errorhandling
+
+class MyErrorBody(value: Int, message: String?)

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/web/servlet/springmvc/errorhandling/MyException.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.web.servlet.springmvc.errorhandling
+
+class MyException: RuntimeException()

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/web/servlet/springmvc/errorhandling/SomeController.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.web.servlet.springmvc.errorhandling
+
+class SomeController

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/web/servlet/springmvc/errorhandling/errorpageswithoutspringmvc/SomeController.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.web.servlet.springmvc.errorhandling.errorpageswithoutspringmvc
+
+class SomeController

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/build.gradle

@@ -54,7 +54,6 @@ dependencies {
 	testImplementation("org.assertj:assertj-core")
 	testImplementation("org.graalvm.buildtools:native-gradle-plugin")
 	testImplementation("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
-	testImplementation("org.jetbrains.kotlin:kotlin-compiler-embeddable:$kotlinVersion")
 	testImplementation("org.jetbrains.kotlin:kotlin-compiler-runner:$kotlinVersion")
 	testImplementation("org.jetbrains.kotlin:kotlin-daemon-client:$kotlinVersion")
 	testImplementation("org.junit.jupiter:junit-jupiter")

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/KotlinPluginAction.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -49,7 +49,7 @@ class KotlinPluginAction implements PluginApplicationAction {
 	private void enableJavaParametersOption(Project project) {
 		project.getTasks()
 			.withType(KotlinCompile.class)
-			.configureEach((compile) -> compile.getKotlinOptions().setJavaParameters(true));
+			.configureEach((compile) -> compile.getCompilerOptions().getJavaParameters().set(true));
 	}
 
 	@Override

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/junit/GradleMultiDslExtension.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,7 +30,6 @@ import org.springframework.boot.gradle.testkit.PluginClasspathGradleBuild;
 import org.springframework.boot.testsupport.gradle.testkit.Dsl;
 import org.springframework.boot.testsupport.gradle.testkit.GradleBuild;
 import org.springframework.boot.testsupport.gradle.testkit.GradleBuildExtension;
-import org.springframework.boot.testsupport.gradle.testkit.GradleVersions;
 
 /**
  * {@link Extension} that runs {@link TestTemplate templated tests} against the Groovy and
@@ -61,8 +60,7 @@ public class GradleMultiDslExtension implements TestTemplateInvocationContextPro
 
 		@Override
 		public List<Extension> getAdditionalExtensions() {
-			GradleBuild gradleBuild = new PluginClasspathGradleBuild(this.dsl)
+			GradleBuild gradleBuild = new PluginClasspathGradleBuild(this.dsl);
-				.gradleVersion(GradleVersions.minimumCompatible());
 			return Arrays.asList(new GradleBuildFieldSetter(gradleBuild), new GradleBuildExtension());
 		}
 

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/KotlinPluginActionIntegrationTests.java

@@ -43,7 +43,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 @ExtendWith(GradleBuildExtension.class)
 class KotlinPluginActionIntegrationTests {
 
-	GradleBuild gradleBuild = new PluginClasspathGradleBuild();
+	GradleBuild gradleBuild = new PluginClasspathGradleBuild().kotlin();
 
 	@Test
 	void noKotlinVersionPropertyWithoutKotlinPlugin() {
@@ -87,7 +87,7 @@ class KotlinPluginActionIntegrationTests {
 				configured.add(line.substring("Configuring :".length()));
 			}
 		}
-		assertThat(configured).containsExactlyInAnyOrder("help", "compileJava", "clean");
+		assertThat(configured).containsExactlyInAnyOrder("help", "clean");
 	}
 
 	private void expectConfigurationCacheRequestedDeprecationWarning() {

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/testkit/PluginClasspathGradleBuild.java

@@ -18,7 +18,7 @@ package org.springframework.boot.gradle.testkit;
 
 import java.io.File;
 import java.io.IOException;
-import java.util.Arrays;
+import java.util.ArrayList;
 import java.util.List;
 
 import com.fasterxml.jackson.annotation.JsonView;
@@ -55,6 +55,8 @@ import org.springframework.boot.testsupport.gradle.testkit.GradleBuild;
  */
 public class PluginClasspathGradleBuild extends GradleBuild {
 
+	private boolean kotlin = false;
+
 	public PluginClasspathGradleBuild() {
 		super();
 	}
@@ -63,35 +65,53 @@ public class PluginClasspathGradleBuild extends GradleBuild {
 		super(dsl);
 	}
 
+	public PluginClasspathGradleBuild kotlin() {
+		this.kotlin = true;
+		return this;
+	}
+
 	@Override
 	public GradleRunner prepareRunner(String... arguments) throws IOException {
 		return super.prepareRunner(arguments).withPluginClasspath(pluginClasspath());
 	}
 
 	private List<File> pluginClasspath() {
-		return Arrays.asList(new File("bin/main"), new File("build/classes/java/main"),
+		List<File> classpath = new ArrayList<>();
-				new File("build/resources/main"), new File(pathOfJarContaining(LaunchScript.class)),
+		classpath.add(new File("bin/main"));
-				new File(pathOfJarContaining(ClassVisitor.class)),
+		classpath.add(new File("build/classes/java/main"));
-				new File(pathOfJarContaining(DependencyManagementPlugin.class)),
+		classpath.add(new File("build/resources/main"));
-				new File(pathOfJarContaining("org.jetbrains.kotlin.cli.common.PropertiesKt")),
+		classpath.add(new File(pathOfJarContaining(LaunchScript.class)));
-				new File(pathOfJarContaining(KotlinPlatformJvmPlugin.class)),
+		classpath.add(new File(pathOfJarContaining(ClassVisitor.class)));
-				new File(pathOfJarContaining(KotlinProject.class)),
+		classpath.add(new File(pathOfJarContaining(DependencyManagementPlugin.class)));
-				new File(pathOfJarContaining(KotlinToolingVersion.class)),
+		if (this.kotlin) {
-				new File(pathOfJarContaining("org.jetbrains.kotlin.daemon.client.KotlinCompilerClient")),
+			classpath.add(new File(pathOfJarContaining("org.jetbrains.kotlin.cli.common.PropertiesKt")));
-				new File(pathOfJarContaining(KotlinCompilerPluginSupportPlugin.class)),
+			classpath.add(new File(pathOfJarContaining(KotlinPlatformJvmPlugin.class)));
-				new File(pathOfJarContaining(LanguageSettings.class)),
+			classpath.add(new File(pathOfJarContaining(KotlinProject.class)));
-				new File(pathOfJarContaining(ArchiveEntry.class)), new File(pathOfJarContaining(BuildRequest.class)),
+			classpath.add(new File(pathOfJarContaining(KotlinToolingVersion.class)));
-				new File(pathOfJarContaining(HttpClientConnectionManager.class)),
+			classpath.add(new File(pathOfJarContaining("org.jetbrains.kotlin.build.report.metrics.BuildTime")));
-				new File(pathOfJarContaining(HttpRequest.class)),
+			classpath.add(new File(pathOfJarContaining("org.jetbrains.kotlin.buildtools.api.CompilationService")));
-				new File(pathOfJarContaining(HttpVersionPolicy.class)), new File(pathOfJarContaining(Module.class)),
+			classpath.add(new File(pathOfJarContaining("org.jetbrains.kotlin.daemon.client.KotlinCompilerClient")));
-				new File(pathOfJarContaining(Versioned.class)),
+			classpath.add(new File(pathOfJarContaining("org.jetbrains.kotlin.konan.library.KonanLibrary")));
-				new File(pathOfJarContaining(ParameterNamesModule.class)),
+			classpath.add(new File(pathOfJarContaining(KotlinCompilerPluginSupportPlugin.class)));
-				new File(pathOfJarContaining("com.github.openjson.JSONObject")),
+			classpath.add(new File(pathOfJarContaining(LanguageSettings.class)));
-				new File(pathOfJarContaining(JsonView.class)), new File(pathOfJarContaining(Platform.class)),
+		}
-				new File(pathOfJarContaining(Toml.class)), new File(pathOfJarContaining(Lexer.class)),
+		classpath.add(new File(pathOfJarContaining(ArchiveEntry.class)));
-				new File(pathOfJarContaining("org.graalvm.buildtools.gradle.NativeImagePlugin")),
+		classpath.add(new File(pathOfJarContaining(BuildRequest.class)));
-				new File(pathOfJarContaining("org.graalvm.reachability.GraalVMReachabilityMetadataRepository")),
+		classpath.add(new File(pathOfJarContaining(HttpClientConnectionManager.class)));
-				new File(pathOfJarContaining("org.graalvm.buildtools.utils.SharedConstants")));
+		classpath.add(new File(pathOfJarContaining(HttpRequest.class)));
+		classpath.add(new File(pathOfJarContaining(HttpVersionPolicy.class)));
+		classpath.add(new File(pathOfJarContaining(Module.class)));
+		classpath.add(new File(pathOfJarContaining(Versioned.class)));
+		classpath.add(new File(pathOfJarContaining(ParameterNamesModule.class)));
+		classpath.add(new File(pathOfJarContaining("com.github.openjson.JSONObject")));
+		classpath.add(new File(pathOfJarContaining(JsonView.class)));
+		classpath.add(new File(pathOfJarContaining(Platform.class)));
+		classpath.add(new File(pathOfJarContaining(Toml.class)));
+		classpath.add(new File(pathOfJarContaining(Lexer.class)));
+		classpath.add(new File(pathOfJarContaining("org.graalvm.buildtools.gradle.NativeImagePlugin")));
+		classpath.add(new File(pathOfJarContaining("org.graalvm.reachability.GraalVMReachabilityMetadataRepository")));
+		classpath.add(new File(pathOfJarContaining("org.graalvm.buildtools.utils.SharedConstants")));
+		return classpath;
 	}
 
 	private String pathOfJarContaining(String className) {

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/KotlinPluginActionIntegrationTests-kotlinCompileTasksCanOverrideDefaultJavaParametersFlag.gradle

@@ -4,16 +4,18 @@ plugins {
 
 apply plugin: 'org.jetbrains.kotlin.jvm'
 
-import org.jetbrains.kotlin.gradle.dsl.KotlinCompile
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 tasks.withType(KotlinCompile) {
-	kotlinOptions.javaParameters = false
+	compilerOptions {
+		javaParameters = false
+	}
 }
 
 task('kotlinCompileTasksJavaParameters') {
 	doFirst {
 		tasks.withType(KotlinCompile) {
-			println "${name} java parameters: ${kotlinOptions.javaParameters}"
+			println "${name} java parameters: ${compilerOptions.javaParameters.get()}"
 		}
 	}
 }

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/KotlinPluginActionIntegrationTests-kotlinCompileTasksUseJavaParametersFlagByDefault.gradle

@@ -4,12 +4,12 @@ plugins {
 
 apply plugin: 'org.jetbrains.kotlin.jvm'
 
-import org.jetbrains.kotlin.gradle.dsl.KotlinCompile
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 task('kotlinCompileTasksJavaParameters') {
 	doFirst {
 		tasks.withType(KotlinCompile) {
-			println "${name} java parameters: ${kotlinOptions.javaParameters}"
+			println "${name} java parameters: ${compilerOptions.javaParameters.get()}"
 		}
 	}
 }