Allow adding <extensions>true</extensions> to plugin config

See gh-921

initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/maven/MavenBuildWriter.java

@@ -43,6 +43,7 @@ import io.spring.initializr.generator.version.VersionReference;
  *
  * @author Andy Wilkinson
  * @author Stephane Nicoll
+ * @author Olga Maciaszek-Sharma
  */
 public class MavenBuildWriter {
 
@@ -270,6 +271,9 @@ public class MavenBuildWriter {
 			writeSingleElement(writer, "groupId", plugin.getGroupId());
 			writeSingleElement(writer, "artifactId", plugin.getArtifactId());
 			writeSingleElement(writer, "version", plugin.getVersion());
+			if (plugin.shouldLoadExtensions()) {
+				writeSingleElement(writer, "extensions", Boolean.toString(true));
+			}
 			writePluginConfiguration(writer, plugin.getConfiguration());
 			if (!plugin.getExecutions().isEmpty()) {
 				writeElement(writer, "executions", () -> writeCollection(writer,

initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/maven/MavenPlugin.java

@@ -28,6 +28,7 @@ import java.util.stream.Collectors;
  * A plugin in a {@link MavenBuild}.
  *
  * @author Andy Wilkinson
+ * @author Olga Maciaszek-Sharma
  */
 public class MavenPlugin {
 
@@ -43,6 +44,8 @@ public class MavenPlugin {
 
 	private ConfigurationCustomization configurationCustomization = null;
 
+	private boolean extensions;
+
 	public MavenPlugin(String groupId, String artifactId) {
 		this(groupId, artifactId, null);
 	}
@@ -99,6 +102,17 @@ public class MavenPlugin {
 				: this.configurationCustomization.build();
 	}
 
+	public boolean shouldLoadExtensions() {
+		return this.extensions;
+	}
+
+	/**
+	 * Enables loading plugin extensions.
+	 */
+	public void extensions() {
+		this.extensions = true;
+	}
+
 	/**
 	 * Builder for creation an {@link Execution}.
 	 */

initializr-generator/src/test/java/io/spring/initializr/generator/buildsystem/maven/MavenBuildTests.java

@@ -24,6 +24,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link MavenBuild}.
  *
  * @author Stephane Nicoll
+ * @author Olga Maciaszek-Sharma
  */
 class MavenBuildTests {
 
@@ -94,4 +95,24 @@ class MavenBuildTests {
 				.containsExactly("run-this", "run-that");
 	}
 
+	@Test
+	void mavenPluginExtensionsNotLoadedByDefault() {
+		MavenBuild build = new MavenBuild();
+		build.plugin("com.example", "test-plugin");
+
+		MavenPlugin testPlugin = build.getPlugins().get(0);
+
+		assertThat(testPlugin.shouldLoadExtensions()).isFalse();
+	}
+
+	@Test
+	void mavenPluginExtensionsCanBeLoaded() {
+		MavenBuild build = new MavenBuild();
+		build.plugin("com.example", "test-plugin").extensions();
+
+		MavenPlugin testPlugin = build.getPlugins().get(0);
+
+		assertThat(testPlugin.shouldLoadExtensions()).isTrue();
+	}
+
 }

initializr-generator/src/test/java/io/spring/initializr/generator/buildsystem/maven/MavenBuildWriterTests.java

@@ -34,6 +34,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link MavenBuildWriter}.
  *
  * @author Stephane Nicoll
+ * @author Olga Maciaszek-Sharma
  */
 class MavenBuildWriterTests {
 
@@ -381,6 +382,7 @@ class MavenBuildWriterTests {
 			assertThat(plugin).textAtPath("artifactId")
 					.isEqualTo("spring-boot-maven-plugin");
 			assertThat(plugin).textAtPath("version").isNullOrEmpty();
+			assertThat(plugin).textAtPath("extensions").isNullOrEmpty();
 		});
 	}
 
@@ -460,6 +462,21 @@ class MavenBuildWriterTests {
 		});
 	}
 
+	@Test
+	void pomWithPluginWithExtensions() throws Exception {
+		MavenBuild build = new MavenBuild();
+		build.setGroup("com.example.demo");
+		build.setArtifact("demo");
+		MavenPlugin demoPlugin = build.plugin("com.example.demo", "demo-plugin");
+		demoPlugin.extensions();
+		generatePom(build, (pom) -> {
+			NodeAssert plugin = pom.nodeAtPath("/project/build/plugins/plugin");
+			assertThat(plugin).textAtPath("groupId").isEqualTo("com.example.demo");
+			assertThat(plugin).textAtPath("artifactId").isEqualTo("demo-plugin");
+			assertThat(plugin).textAtPath("extensions").isEqualTo(Boolean.toString(true));
+		});
+	}
+
 	@Test
 	void pomWithMavenCentral() throws Exception {
 		MavenBuild build = new MavenBuild();