Make sure that Maven plugin configuration can be amended

See gh-867

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/code/kotlin/KotlinJpaMavenBuildCustomizer.java

@@ -41,9 +41,9 @@ public class KotlinJpaMavenBuildCustomizer implements BuildCustomizer<MavenBuild
 		if (this.buildMetadataResolver.hasFacet(build, "jpa")) {
 			MavenPlugin kotlinNoArgPlugin = build.plugin("org.jetbrains.kotlin",
 					"kotlin-maven-noarg", "${kotlin.version}");
-			kotlinNoArgPlugin
+			kotlinNoArgPlugin.configuration((configuration) -> configuration.parameter(
-					.configuration((configuration) -> configuration.add("compilerPlugins",
+					"compilerPlugins",
-							(compilerPlugins) -> compilerPlugins.add("plugin", "jpa")));
+					(compilerPlugins) -> compilerPlugins.parameter("plugin", "jpa")));
 		}
 	}
 

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/code/kotlin/KotlinMavenBuildCustomizer.java

@@ -45,10 +45,10 @@ class KotlinMavenBuildCustomizer implements BuildCustomizer<MavenBuild> {
 		MavenPlugin kotlinMavenPlugin = build.plugin("org.jetbrains.kotlin",
 				"kotlin-maven-plugin");
 		kotlinMavenPlugin.configuration((configuration) -> {
-			configuration.add("args", (args) -> this.settings.getCompilerArgs()
+			configuration.parameter("args", (args) -> this.settings.getCompilerArgs()
-					.forEach((arg) -> args.add("arg", arg)));
+					.forEach((arg) -> args.parameter("arg", arg)));
-			configuration.add("compilerPlugins",
+			configuration.parameter("compilerPlugins",
-					(compilerPlugins) -> compilerPlugins.add("plugin", "spring"));
+					(compilerPlugins) -> compilerPlugins.parameter("plugin", "spring"));
 		});
 		kotlinMavenPlugin.dependency("org.jetbrains.kotlin", "kotlin-maven-allopen",
 				"${kotlin.version}");

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/code/kotlin/KotlinMavenFullBuildCustomizer.java

@@ -42,11 +42,11 @@ class KotlinMavenFullBuildCustomizer implements BuildCustomizer<MavenBuild> {
 		MavenPlugin kotlinMavenPlugin = build.plugin("org.jetbrains.kotlin",
 				"kotlin-maven-plugin", "${kotlin.version}");
 		kotlinMavenPlugin.configuration((configuration) -> {
-			configuration.add("args", (args) -> this.settings.getCompilerArgs()
+			configuration.parameter("args", (args) -> this.settings.getCompilerArgs()
-					.forEach((arg) -> args.add("arg", arg)));
+					.forEach((arg) -> args.parameter("arg", arg)));
-			configuration.add("compilerPlugins",
+			configuration.parameter("compilerPlugins",
-					(compilerPlugins) -> compilerPlugins.add("plugin", "spring"));
+					(compilerPlugins) -> compilerPlugins.parameter("plugin", "spring"));
-			configuration.add("jvmTarget", this.settings.getJvmTarget());
+			configuration.parameter("jvmTarget", this.settings.getJvmTarget());
 		});
 		kotlinMavenPlugin.execution("compile",
 				(compile) -> compile.phase("compile").goal("compile"));

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

@@ -18,8 +18,11 @@ package io.spring.initializr.generator.buildsystem.maven;
 
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
+import java.util.stream.Collectors;
 
 /**
  * A plugin in a {@link MavenBuild}.
@@ -139,23 +142,58 @@ public class MavenPlugin {
 	 */
 	public static class ConfigurationCustomization {
 
-		private final List<Setting> settings = new ArrayList<>();
+		private final Map<String, Object> settings = new LinkedHashMap<>();
 
-		public ConfigurationCustomization add(String key, String value) {
+		/**
-			this.settings.add(new Setting(key, value));
+		 * Set the specified parameter with a single value.
+		 * @param name the name of the parameter
+		 * @param value the single value of the parameter
+		 * @return this for method chaining
+		 */
+		public ConfigurationCustomization parameter(String name, String value) {
+			this.settings.put(name, value);
 			return this;
 		}
 
-		public ConfigurationCustomization add(String key,
+		/**
+		 * Configure the parameter with the specified {@code name}.
+		 * @param parameter the name of the parameter
+		 * @param consumer a consumer to further configure the parameter
+		 * @return this for method chaining
+		 * @throws IllegalArgumentException if a parameter with the same name is
+		 * registered with a single value
+		 */
+		public ConfigurationCustomization parameter(String parameter,
 				Consumer<ConfigurationCustomization> consumer) {
-			ConfigurationCustomization nestedConfiguration = new ConfigurationCustomization();
+			Object value = this.settings.computeIfAbsent(parameter,
+					(id) -> new ConfigurationCustomization());
+			if (!(value instanceof ConfigurationCustomization)) {
+				throw new IllegalArgumentException(String.format(
+						"Could not customize parameter '%s', a single value %s is already registered",
+						parameter, value));
+			}
+			ConfigurationCustomization nestedConfiguration = (ConfigurationCustomization) value;
 			consumer.accept(nestedConfiguration);
-			this.settings.add(new Setting(key, nestedConfiguration.settings));
 			return this;
 		}
 
 		Configuration build() {
-			return new Configuration(this.settings);
+			return new Configuration(this.settings.entrySet().stream()
+					.map((entry) -> resolve(entry.getKey(), entry.getValue()))
+					.collect(Collectors.toList()));
+		}
+
+		private Setting resolve(String key, Object value) {
+			if (value instanceof ConfigurationCustomization) {
+				List<Setting> values = ((ConfigurationCustomization) value).settings
+						.entrySet().stream()
+						.map((entry) -> resolve(entry.getKey(), entry.getValue()))
+						.collect(Collectors.toList());
+				return new Setting(key, values);
+			}
+			else {
+				return new Setting(key, value);
+			}
 		}
 
 	}

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

@@ -336,9 +336,10 @@ class MavenBuildWriterTests {
 		build.setArtifact("demo");
 		MavenPlugin kotlin = build.plugin("org.jetbrains.kotlin", "kotlin-maven-plugin");
 		kotlin.configuration((configuration) -> {
-			configuration.add("args", (args) -> args.add("arg", "-Xjsr305=strict"));
+			configuration.parameter("args",
-			configuration.add("compilerPlugins",
+					(args) -> args.parameter("arg", "-Xjsr305=strict"));
-					(compilerPlugins) -> compilerPlugins.add("plugin", "spring"));
+			configuration.parameter("compilerPlugins",
+					(compilerPlugins) -> compilerPlugins.parameter("plugin", "spring"));
 		});
 		generatePom(build, (pom) -> {
 			NodeAssert plugin = pom.nodeAtPath("/project/build/plugins/plugin");
@@ -363,8 +364,8 @@ class MavenBuildWriterTests {
 			execution.goal("process-asciidoc");
 			execution.phase("generateProject-resources");
 			execution.configuration((configuration) -> {
-				configuration.add("doctype", "book");
+				configuration.parameter("doctype", "book");
-				configuration.add("backend", "html");
+				configuration.parameter("backend", "html");
 			});
 		});
 		generatePom(build, (pom) -> {

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

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2012-2019 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 io.spring.initializr.generator.buildsystem.maven;
+
+import java.util.List;
+
+import io.spring.initializr.generator.buildsystem.maven.MavenPlugin.Setting;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link MavenPlugin}.
+ *
+ * @author Stephane Nicoll
+ */
+class MavenPluginTests {
+
+	@Test
+	void configurationCanBeCustomized() {
+		MavenPlugin plugin = new MavenPlugin("com.example", "test-plugin");
+		plugin.configuration((customizer) -> customizer.parameter("enabled", "false")
+				.parameter("skip", "true"));
+		plugin.configuration((customizer) -> customizer.parameter("another", "test"));
+		assertThat(plugin.getConfiguration().getSettings().stream().map(Setting::getName))
+				.containsExactly("enabled", "skip", "another");
+		assertThat(
+				plugin.getConfiguration().getSettings().stream().map(Setting::getValue))
+						.containsExactly("false", "true", "test");
+	}
+
+	@Test
+	void configurationCanBeOverridden() {
+		MavenPlugin plugin = new MavenPlugin("com.example", "test-plugin");
+		plugin.configuration((customizer) -> customizer.parameter("enabled", "true"));
+		plugin.configuration((customizer) -> customizer.parameter("enabled", "false"));
+		assertThat(plugin.getConfiguration().getSettings().stream().map(Setting::getName))
+				.containsExactly("enabled");
+		assertThat(
+				plugin.getConfiguration().getSettings().stream().map(Setting::getValue))
+						.containsExactly("false");
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	void configurationWithNestedValuesCanBeCustomized() {
+		MavenPlugin plugin = new MavenPlugin("com.example", "test-plugin");
+		plugin.configuration((customizer) -> customizer.parameter("items",
+				(items) -> items.parameter("one", "true")));
+		plugin.configuration((customizer) -> customizer.parameter("items",
+				(items) -> items.parameter("two", "false")));
+		assertThat(plugin.getConfiguration().getSettings()).hasSize(1);
+		Setting setting = plugin.getConfiguration().getSettings().get(0);
+		assertThat(setting.getName()).isEqualTo("items");
+		assertThat(setting.getValue()).isInstanceOf(List.class);
+		List<Setting> values = (List<Setting>) setting.getValue();
+		assertThat(values.stream().map(Setting::getName)).containsExactly("one", "two");
+		assertThat(values.stream().map(Setting::getValue)).containsExactly("true",
+				"false");
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	void configurationWithSeveralLevelOfNestedValuesCanBeCustomized() {
+		MavenPlugin plugin = new MavenPlugin("com.example", "test-plugin");
+		plugin.configuration((customizer) -> customizer.parameter("items",
+				(items) -> items.parameter("subItems",
+						(subItems) -> subItems.parameter("one", "true"))));
+		plugin.configuration((customizer) -> customizer.parameter("items",
+				(items) -> items.parameter("subItems", (subItems) -> subItems
+						.parameter("one", "false").parameter("two", "true"))));
+		assertThat(plugin.getConfiguration().getSettings()).hasSize(1);
+		Setting setting = plugin.getConfiguration().getSettings().get(0);
+		assertThat(setting.getName()).isEqualTo("items");
+		assertThat(setting.getValue()).isInstanceOf(List.class);
+		List<Setting> items = (List<Setting>) setting.getValue();
+		assertThat(items).hasSize(1);
+		Setting item = items.get(0);
+		assertThat(item.getName()).isEqualTo("subItems");
+		assertThat(item.getValue()).isInstanceOf(List.class);
+		List<Setting> subItems = (List<Setting>) item.getValue();
+		assertThat(subItems.stream().map(Setting::getName)).containsExactly("one", "two");
+		assertThat(subItems.stream().map(Setting::getValue)).containsExactly("false",
+				"true");
+	}
+
+	@Test
+	void configurationCannotBeSwitchedToNestedValue() {
+		MavenPlugin plugin = new MavenPlugin("com.example", "test-plugin");
+		plugin.configuration((customizer) -> customizer.parameter("test", "value"));
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> plugin.configuration((customizer) -> customizer
+						.parameter("test", (test) -> test.parameter("one", "true"))))
+				.withMessageContaining("test").withMessageContaining("value");
+	}
+
+}