Fail fast when plugin is used with an unsupported version of Gradle

Closes gh-8820

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

@@ -19,10 +19,12 @@ package org.springframework.boot.gradle.plugin;
 import java.util.Arrays;
 import java.util.List;
 
+import org.gradle.api.GradleException;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.component.SoftwareComponent;
+import org.gradle.util.GradleVersion;
 
 import org.springframework.boot.gradle.dsl.SpringBootExtension;
 import org.springframework.boot.gradle.tasks.bundling.BootJar;
@@ -74,9 +76,31 @@ public class SpringBootPlugin implements Plugin<Project> {
 
 	@Override
 	public void apply(Project project) {
+		verifyGradleVersion();
+		createExtension(project);
+		Configuration bootArchives = createBootArchivesConfiguration(project);
+		registerPluginActions(project, bootArchives);
+		unregisterUnresolvedDependenciesAnalyzer(project);
+	}
+
+	private void verifyGradleVersion() {
+		if (GradleVersion.current().compareTo(GradleVersion.version("3.4")) < 0) {
+			throw new GradleException("Spring Boot plugin requires Gradle 3.4 or later."
+					+ " The current version is " + GradleVersion.current());
+		}
+	}
+
+	private void createExtension(Project project) {
 		project.getExtensions().create("springBoot", SpringBootExtension.class, project);
+	}
+
+	private Configuration createBootArchivesConfiguration(Project project) {
 		Configuration bootArchives = project.getConfigurations()
 				.create(BOOT_ARCHIVES_CONFIGURATION_NAME);
+		return bootArchives;
+	}
+
+	private void registerPluginActions(Project project, Configuration bootArchives) {
 		SinglePublishedArtifact singlePublishedArtifact = new SinglePublishedArtifact(
 				bootArchives.getArtifacts());
 		List<PluginApplicationAction> actions = Arrays.asList(
@@ -88,6 +112,9 @@ public class SpringBootPlugin implements Plugin<Project> {
 			project.getPlugins().withType(action.getPluginClass(),
 					plugin -> action.execute(project));
 		}
+	}
+
+	private void unregisterUnresolvedDependenciesAnalyzer(Project project) {
 		UnresolvedDependenciesAnalyzer unresolvedDependenciesAnalyzer = new UnresolvedDependenciesAnalyzer();
 		project.getConfigurations().all(configuration -> configuration.getIncoming()
 				.afterResolve(resolvableDependencies -> unresolvedDependenciesAnalyzer

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

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2012-2017 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
+ *
+ *      http://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.gradle.plugin;
+
+import org.gradle.testkit.runner.BuildResult;
+import org.junit.Rule;
+import org.junit.Test;
+
+import org.springframework.boot.gradle.testkit.GradleBuild;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for {@link SpringBootPlugin}.
+ *
+ * @author Andy Wilkinson
+ */
+public class SpringBootPluginIntegrationTests {
+
+	@Rule
+	public final GradleBuild gradleBuild = new GradleBuild();
+
+	@Test
+	public void failFastWithVersionOfGradleLowerThanRequired() {
+		BuildResult result = this.gradleBuild.gradleVersion("3.3").buildAndFail();
+		assertThat(result.getOutput()).contains("Spring Boot plugin requires Gradle 3.4"
+				+ " or later. The current version is Gradle 3.3");
+	}
+
+	@Test
+	public void succeedWithVersionOfGradleHigherThanRequired() {
+		this.gradleBuild.gradleVersion("3.5-rc-3").build();
+	}
+
+	@Test
+	public void succeedWithVersionOfGradleMatchingWhatIsRequired() {
+		this.gradleBuild.gradleVersion("3.4").build();
+	}
+
+}

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

@@ -55,6 +55,8 @@ public class GradleBuild implements TestRule {
 
 	private String script;
 
+	private String gradleVersion;
+
 	@Override
 	public Statement apply(Statement base, Description description) {
 		URL scriptUrl = findDefaultScript(description);
@@ -149,6 +151,9 @@ public class GradleBuild implements TestRule {
 				new FileWriter(new File(this.projectDir, "build.gradle")));
 		GradleRunner gradleRunner = GradleRunner.create().withProjectDir(this.projectDir)
 				.forwardOutput();
+		if (this.gradleVersion != null) {
+			gradleRunner.withGradleVersion(this.gradleVersion);
+		}
 		List<String> allArguments = new ArrayList<String>();
 		allArguments.add("-PpluginClasspath=" + pluginClasspath());
 		allArguments.add("-PbootVersion=" + getBootVersion());
@@ -164,6 +169,11 @@ public class GradleBuild implements TestRule {
 		this.projectDir = projectDir;
 	}
 
+	public GradleBuild gradleVersion(String version) {
+		this.gradleVersion = version;
+		return this;
+	}
+
 	private static String getBootVersion() {
 		return evaluateExpression(
 				"/*[local-name()='project']/*[local-name()='parent']/*[local-name()='version']"

spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/SpringBootPluginIntegrationTests.gradle

@@ -0,0 +1,7 @@
+buildscript {
+	dependencies {
+		classpath files(pluginClasspath.split(','))
+	}
+}
+
+apply plugin: 'org.springframework.boot'