Configure Spring JavaFormat in Gradle build

This commit creates a new build convention that applies the Spring
JavaFormat Gradle plugin.
This is also adding a default checkstyle configuration for this project.

See gh-54

.gitignore

@@ -1,4 +1,5 @@
 build
+!/**/src/**/build
 .gradle
 .idea/
 out

buildSrc/build.gradle

@@ -0,0 +1,38 @@
+plugins {
+	id "java-gradle-plugin"
+	id "io.spring.javaformat" version "${javaFormatVersion}"
+	id "checkstyle"
+}
+
+repositories {
+	mavenCentral()
+	gradlePluginPortal()
+	maven { url "https://repo.spring.io/release" }
+}
+
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
+
+dependencies {
+	checkstyle "io.spring.javaformat:spring-javaformat-checkstyle:${javaFormatVersion}"
+	implementation("io.spring.javaformat:spring-javaformat-gradle-plugin:${javaFormatVersion}")
+}
+
+checkstyle {
+	def archive = configurations.checkstyle.filter { it.name.startsWith("spring-javaformat-checkstyle")}
+	config = resources.text.fromArchiveEntry(archive, "io/spring/javaformat/checkstyle/checkstyle.xml")
+	toolVersion = 8.11
+}
+
+gradlePlugin {
+	plugins {
+		conventionsPlugin {
+			id = "org.springframework.graphql.conventions"
+			implementationClass = "org.springframework.graphql.build.ConventionsPlugin"
+		}
+	}
+}
+
+test {
+	useJUnitPlatform()
+}

buildSrc/gradle.properties

@@ -0,0 +1 @@
+javaFormatVersion=0.0.28

buildSrc/settings.gradle

@@ -0,0 +1,13 @@
+pluginManagement {
+	repositories {
+		mavenCentral()
+		gradlePluginPortal()
+	}
+	resolutionStrategy {
+		eachPlugin {
+			if (requested.id.id == "io.spring.javaformat") {
+				useModule "io.spring.javaformat:spring-javaformat-gradle-plugin:${requested.version}"
+			}
+		}
+	}
+}

buildSrc/src/main/java/org/springframework/graphql/build/ConventionsPlugin.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2020-2021 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
+ *
+ *      https://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.graphql.build;
+
+import io.spring.javaformat.gradle.FormatTask;
+import io.spring.javaformat.gradle.SpringJavaFormatPlugin;
+import org.gradle.api.Plugin;
+import org.gradle.api.Project;
+import org.gradle.api.artifacts.DependencySet;
+import org.gradle.api.plugins.JavaBasePlugin;
+import org.gradle.api.plugins.quality.CheckstyleExtension;
+import org.gradle.api.plugins.quality.CheckstylePlugin;
+
+/**
+ * Conventions that are applied in the presence of the {@link JavaBasePlugin}. When the
+ * plugin is applied, the {@link SpringJavaFormatPlugin Spring Java Format} and
+ * {@link CheckstylePlugin Checkstyle}.
+ *
+ * @author Brian Clozel
+ */
+public class ConventionsPlugin implements Plugin<Project> {
+
+	@Override
+	public void apply(Project project) {
+		project.getPlugins().withType(JavaBasePlugin.class, (java) -> applySpringJavaFormat(project));
+	}
+
+	private void applySpringJavaFormat(Project project) {
+		project.getPlugins().apply(SpringJavaFormatPlugin.class);
+		project.getTasks().withType(FormatTask.class, (formatTask) -> formatTask.setEncoding("UTF-8"));
+		project.getPlugins().apply(CheckstylePlugin.class);
+		CheckstyleExtension checkstyle = project.getExtensions().getByType(CheckstyleExtension.class);
+		checkstyle.setToolVersion("8.43");
+		checkstyle.getConfigDirectory().set(project.getRootProject().file("src/checkstyle"));
+		String version = SpringJavaFormatPlugin.class.getPackage().getImplementationVersion();
+		DependencySet checkstyleDependencies = project.getConfigurations().getByName("checkstyle").getDependencies();
+		checkstyleDependencies
+				.add(project.getDependencies().create("io.spring.javaformat:spring-javaformat-checkstyle:" + version));
+	}
+
+}

src/checkstyle/checkstyle-suppressions.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0"?>
+<!DOCTYPE suppressions PUBLIC "-//Checkstyle//DTD SuppressionFilter Configuration 1.2//EN" "https://checkstyle.org/dtds/suppressions_1_2.dtd">
+<suppressions>
+	<!-- generated sources -->
+	<suppress files="[\\/]build[\\/]generated[\\/]sources[\\/]" checks=".*" />
+
+</suppressions>

src/checkstyle/checkstyle.xml

@@ -0,0 +1,53 @@
+<?xml version="1.0"?>
+<!DOCTYPE module PUBLIC
+		"-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+		"https://checkstyle.org/dtds/configuration_1_3.dtd">
+<module name="com.puppycrawl.tools.checkstyle.Checker">
+	<module name="SuppressionFilter">
+		<property name="file" value="${config_loc}/checkstyle-suppressions.xml"/>
+	</module>
+	<module name="io.spring.javaformat.checkstyle.SpringChecks" />
+	<module name="com.puppycrawl.tools.checkstyle.TreeWalker">
+		<module name="io.spring.javaformat.checkstyle.check.SpringJUnit5Check" />
+		<module
+				name="com.puppycrawl.tools.checkstyle.checks.imports.IllegalImportCheck">
+			<property name="id" value="mainCodeIllegalImportCheck"/>
+			<property name="regexp" value="true" />
+			<property name="illegalClasses"
+					  value="^javax.annotation.PostConstruct"/>
+		</module>
+		<module
+				name="com.puppycrawl.tools.checkstyle.checks.imports.ImportControlCheck">
+			<property name="file"
+					  value="${config_loc}/import-control.xml" />
+			<property name="path" value="^.*[\\/]src[\\/]main[\\/].*$" />
+		</module>
+		<module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+			<property name="maximum" value="0"/>
+			<property name="format" value="org\.junit\.Assert\.assert" />
+			<property name="message"
+					  value="Please use AssertJ imports." />
+			<property name="ignoreComments" value="true" />
+		</module>
+		<module
+				name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+			<property name="maximum" value="0" />
+			<property name="format"
+					  value="assertThatExceptionOfType\((NullPointerException|IllegalArgumentException|IOException|IllegalStateException)\.class\)" />
+			<property name="message"
+					  value="Please use specialized AssertJ assertThat*Exception method." />
+			<property name="ignoreComments" value="true" />
+		</module>
+		<module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+			<property name="maximum" value="0"/>
+			<property name="format" value="org\.mockito\.(Mockito|BDDMockito)\.(when|doThrow|doAnswer)" />
+			<property name="message"
+					  value="Please use BDD-style (given, when, then) using BDDMockito imports." />
+			<property name="ignoreComments" value="true" />
+		</module>
+		<module name="io.spring.javaformat.checkstyle.check.SpringJavadocCheck">
+			<property name="publicOnlySinceTags" value="true" />
+			<property name="requireSinceTag" value="true" />
+		</module>
+	</module>
+</module>

src/checkstyle/import-control.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0"?>
+<!DOCTYPE import-control PUBLIC "-//Checkstyle//DTD ImportControl Configuration 1.4//EN" "https://checkstyle.org/dtds/import_control_1_4.dtd">
+<import-control pkg="org.springframework.graphql">
+	<allow pkg=".*" regex="true" />
+</import-control>