Group build properties under ext

Closes gh-781

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

@@ -420,6 +420,9 @@ public class ProjectGenerator {
 		model.put("buildPropertiesVersions", versions.entrySet());
 		request.getBuildProperties().getVersions().forEach(
 				(k, v) -> versions.put(computeVersionProperty(request, k), v.get()));
+		if (!versions.isEmpty()) {
+			model.put("hasBuildPropertiesVersions", true);
+		}
 		Map<String, String> gradle = new LinkedHashMap<>();
 		model.put("buildPropertiesGradle", gradle.entrySet());
 		request.getBuildProperties().getGradle()

initializr-generator/src/main/resources/templates/starter-build.gradle

@@ -72,9 +72,13 @@ configurations {
 	providedRuntime
 }
 {{/providedDependencies}}
+{{#hasBuildPropertiesVersions}}
+ext {
 {{#buildPropertiesVersions}}
-ext['{{key}}'] = '{{value}}'
+	set('{{key}}', '{{value}}')
 {{/buildPropertiesVersions}}
+}
+{{/hasBuildPropertiesVersions}}
 
 dependencies {
 	{{#compileDependencies}}

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

@@ -718,8 +718,8 @@ public class ProjectGeneratorTests extends AbstractProjectGeneratorTests {
 		request.getBuildProperties().getMaven().put("ignore.property", () -> "yes");
 
 		generateGradleBuild(request).contains("name = 'test'")
-				.contains("ext['foo.version'] = '1.2.3'")
-				.contains("ext['internalVersion'] = '4.5.6'")
+				.contains("set('foo.version', '1.2.3')")
+				.contains("set('internalVersion', '4.5.6')")
 				.doesNotContain("ignore.property");
 	}
 

initializr-generator/src/test/resources/project/gradle/bom-property-build.gradle.gen

@@ -23,7 +23,9 @@ repositories {
 	mavenCentral()
 }
 
-ext['fooVersion'] = '1.3.3'
+ext {
+	set('fooVersion', '1.3.3')
+}
 
 dependencies {
 	implementation('org.acme:foo')

initializr-generator/src/test/resources/project/gradle/version-override-build.gradle.gen

@@ -23,8 +23,10 @@ repositories {
 	mavenCentral()
 }
 
-ext['springBarVersion'] = '0.2.0.RELEASE'
-ext['spring-foo.version'] = '0.1.0.RELEASE'
+ext {
+	set('springBarVersion', '0.2.0.RELEASE')
+	set('spring-foo.version', '0.1.0.RELEASE')
+}
 
 dependencies {
 	implementation('org.springframework.boot:spring-boot-starter-web')