Make kotlin version mandatory only if Kotlin is enabled

Closes gh-617

initializr-docs/src/main/asciidoc/configuration-format.adoc

@@ -45,7 +45,7 @@ generation uses one of these names, the default is used instead.
 * `googleAnalyticsTrackingCode`: the Google Analytics code to use. If this is set,
 Google analytics is automatically enabled.
 * `kotlin`: kotlin-specific settings. For now, only the kotlin version to use can be
-configured.
+configured and is a mandatory option if Kotlin is enabled.
 * `maven`: maven-specified settings. A custom maven parent POM can be defined and
 whether or not the `spring-boot-dependencies` BOM should be automatically added to
 the project.

initializr-generator/src/main/java/io/spring/initializr/generator/ProjectGenerator.java

@@ -431,9 +431,9 @@ public class ProjectGenerator {
 		// Add various versions
 		model.put("dependencyManagementPluginVersion", metadata.getConfiguration()
 				.getEnv().getGradle().getDependencyManagementPluginVersion());
-		model.put("kotlinVersion", metadata.getConfiguration().getEnv().getKotlin()
-				.resolveKotlinVersion(bootVersion));
 		if ("kotlin".equals(request.getLanguage())) {
+			model.put("kotlinVersion", metadata.getConfiguration().getEnv().getKotlin()
+					.resolveKotlinVersion(bootVersion));
 			model.put("kotlin", true);
 		}
 		if ("groovy".equals(request.getLanguage())) {

initializr-generator/src/main/java/io/spring/initializr/generator/ProjectRequest.java

@@ -20,6 +20,7 @@ import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
 import io.spring.initializr.metadata.BillOfMaterials;
@@ -228,14 +229,13 @@ public class ProjectRequest extends BasicProjectRequest {
 
 	protected void initializeProperties(InitializrMetadata metadata,
 			Version requestedVersion) {
-		String kotlinVersion = metadata.getConfiguration().getEnv().getKotlin()
+		Supplier<String> kotlinVersion = () -> metadata.getConfiguration().getEnv().getKotlin()
 				.resolveKotlinVersion(requestedVersion);
 		if ("gradle".equals(this.build)) {
 			this.buildProperties.getGradle().put("springBootVersion",
 					this::getBootVersion);
 			if ("kotlin".equals(getLanguage())) {
-				this.buildProperties.getGradle().put("kotlinVersion",
+				this.buildProperties.getGradle().put("kotlinVersion", kotlinVersion);
-						() -> kotlinVersion);
 			}
 		}
 		else {
@@ -247,7 +247,7 @@ public class ProjectRequest extends BasicProjectRequest {
 					this::getJavaVersion);
 			if ("kotlin".equals(getLanguage())) {
 				this.buildProperties.getVersions()
-						.put(new VersionProperty("kotlin.version"), () -> kotlinVersion);
+						.put(new VersionProperty("kotlin.version"), kotlinVersion);
 			}
 		}
 	}

initializr-generator/src/test/java/io/spring/initializr/generator/AbstractProjectGeneratorTests.java

@@ -65,7 +65,7 @@ public abstract class AbstractProjectGeneratorTests {
 	public void setup() throws IOException {
 		Dependency web = Dependency.withId("web");
 		web.getFacets().add("web");
-		InitializrMetadata metadata = InitializrMetadataTestBuilder.withDefaults()
+		InitializrMetadata metadata = initializeTestMetadataBuilder()
 				.addDependencyGroup("web", web).addDependencyGroup("test", "security",
 						"data-jpa", "aop", "batch", "integration")
 				.build();
@@ -76,6 +76,10 @@ public abstract class AbstractProjectGeneratorTests {
 		this.projectGenerator.setTmpdir(this.folder.newFolder().getAbsolutePath());
 	}
 
+	protected InitializrMetadataTestBuilder initializeTestMetadataBuilder() {
+		return InitializrMetadataTestBuilder.withDefaults();
+	}
+
 	protected PomAssert generateMavenPom(ProjectRequest request) {
 		request.setType("maven-build");
 		String content = new String(this.projectGenerator.generateMavenPom(request));

initializr-generator/src/test/java/io/spring/initializr/generator/ProjectGeneratorTests.java

@@ -48,6 +48,11 @@ public class ProjectGeneratorTests extends AbstractProjectGeneratorTests {
 	@Rule
 	public final ExpectedException thrown = ExpectedException.none();
 
+	@Override
+	protected InitializrMetadataTestBuilder initializeTestMetadataBuilder() {
+		return InitializrMetadataTestBuilder.withBasicDefaults();
+	}
+
 	@Test
 	public void defaultMavenPom() {
 		ProjectRequest request = createProjectRequest("web");
@@ -348,6 +353,9 @@ public class ProjectGeneratorTests extends AbstractProjectGeneratorTests {
 		request.setBootVersion("1.1.9.RELEASE");
 		request.setName("MyDemo");
 		request.setPackageName("foo");
+
+		applyMetadata(initializeTestMetadataBuilder().addDependencyGroup("core", "web")
+				.setKotlinEnv("1.0.0").build());
 		generateProject(request)
 				.sourceCodeAssert("src/main/kotlin/foo/MyDemoApplication.kt")
 				.hasImports(EnableAutoConfiguration.class.getName(),
@@ -364,6 +372,9 @@ public class ProjectGeneratorTests extends AbstractProjectGeneratorTests {
 		request.setBootVersion("1.2.0.RC1");
 		request.setName("MyDemo");
 		request.setPackageName("foo");
+
+		applyMetadata(initializeTestMetadataBuilder().addDependencyGroup("core", "web")
+				.setKotlinEnv("1.0.0").build());
 		generateProject(request)
 				.sourceCodeAssert("src/main/kotlin/foo/MyDemoApplication.kt")
 				.hasImports(SpringBootApplication.class.getName())

initializr-generator/src/test/java/io/spring/initializr/test/metadata/InitializrMetadataTestBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -43,7 +43,11 @@ public class InitializrMetadataTestBuilder {
 	private final InitializrMetadataBuilder builder = InitializrMetadataBuilder.create();
 
 	public static InitializrMetadataTestBuilder withDefaults() {
-		return new InitializrMetadataTestBuilder().addDefaults();
+		return new InitializrMetadataTestBuilder().addAllDefaults();
+	}
+
+	public static InitializrMetadataTestBuilder withBasicDefaults() {
+		return new InitializrMetadataTestBuilder().addBasicDefaults();
 	}
 
 	public InitializrMetadata build() {
@@ -75,12 +79,16 @@ public class InitializrMetadataTestBuilder {
 		return this;
 	}
 
-	public InitializrMetadataTestBuilder addDefaults() {
+	public InitializrMetadataTestBuilder addAllDefaults() {
-		return addDefaultTypes().addDefaultPackagings().addDefaultJavaVersions()
+		return addBasicDefaults()
-				.addDefaultLanguages().addDefaultBootVersions()
 				.setGradleEnv("0.5.1.RELEASE").setKotlinEnv("1.1.1");
 	}
 
+	public InitializrMetadataTestBuilder addBasicDefaults() {
+		return addDefaultTypes().addDefaultPackagings().addDefaultJavaVersions()
+				.addDefaultLanguages().addDefaultBootVersions();
+	}
+
 	public InitializrMetadataTestBuilder addDefaultTypes() {
 		return addType("maven-build", false, "/pom.xml", "maven", "build")
 				.addType("maven-project", true, "/starter.zip", "maven", "project")