Add Spring-specific styling to Gradle Plugin's documentation

This commit replaces the default Asciidoctor styling with
Spring specific styling.

First, we need to unzip the contents of the Spring Asciidoctor
documentation resources provided by the
`io.spring.docsresources:spring-docs-resources` distribution zip. This
is done in a `/target/refdocs` folder. We then copy all files from
`src/main/asciidoc` to the same location, and then launch the generation
process.

See gh-16327

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/pom.xml

@@ -16,6 +16,7 @@
 		<gradle.executable>./gradlew</gradle.executable>
 		<gradle.task>build</gradle.task>
 		<skip.gradle.build>false</skip.gradle.build>
+		<refdocs.build.directory>${project.build.directory}/refdocs/</refdocs.build.directory>
 	</properties>
 	<dependencies>
 		<dependency>
@@ -39,6 +40,24 @@
 	</dependencies>
 	<build>
 		<plugins>
+			<plugin>
+				<groupId>com.googlecode.maven-download-plugin</groupId>
+				<artifactId>download-maven-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>unpack-doc-resources</id>
+						<phase>generate-resources</phase>
+						<goals>
+							<goal>wget</goal>
+						</goals>
+						<configuration>
+							<url>https://repo.spring.io/release/io/spring/docresources/spring-doc-resources/${spring-doc-resources.version}/spring-doc-resources-${spring-doc-resources.version}.zip</url>
+							<unpack>true</unpack>
+							<outputDirectory>${refdocs.build.directory}</outputDirectory>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-dependency-plugin</artifactId>
@@ -69,6 +88,28 @@
 					</execution>
 				</executions>
 			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-resources-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>copy-asciidoc-resources</id>
+						<phase>generate-resources</phase>
+						<goals>
+							<goal>copy-resources</goal>
+						</goals>
+						<configuration>
+							<outputDirectory>${refdocs.build.directory}</outputDirectory>
+							<resources>
+								<resource>
+									<directory>src/main/asciidoc</directory>
+									<filtering>false</filtering>
+								</resource>
+							</resources>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
 			<plugin>
 				<groupId>org.codehaus.mojo</groupId>
 				<artifactId>exec-maven-plugin</artifactId>
@@ -233,17 +274,7 @@
 									<target>
 										<zip
 											destfile="${project.build.directory}/${project.artifactId}-${project.version}-docs.zip">
-											<zipfileset
-												src="build/libs/${project.artifactId}-${project.version}-javadoc.jar"
-												prefix="api" />
-											<zipfileset dir="${project.build.directory}/generated-docs"
-												includes="index.html" prefix="reference/html" />
-											<mappedresources>
-												<fileset dir="${project.build.directory}/generated-docs"
-													includes="index.pdf" />
-												<globmapper from="index.pdf"
-													to="reference/pdf/spring-boot-gradle-plugin-reference.pdf" />
-											</mappedresources>
+											<fileset dir="${project.build.directory}/generated-docs" />
 										</zip>
 									</target>
 								</configuration>
@@ -261,7 +292,19 @@
 									<goal>process-asciidoc</goal>
 								</goals>
 								<configuration>
-									<backend>html</backend>
+									<backend>html5</backend>
+									<outputDirectory>${project.build.directory}/generated-docs/reference/html</outputDirectory>
+									<sourceHighlighter>highlight.js</sourceHighlighter>
+									<doctype>book</doctype>
+									<attributes>
+										<highlightjsdir>js/highlight</highlightjsdir>
+										<highlightjs-theme>atom-one-dark-reasonable</highlightjs-theme>
+										<linkcss>true</linkcss>
+										<imagesdir>./images</imagesdir>
+										<icons>font</icons>
+										<stylesdir>css/</stylesdir>
+										<stylesheet>style.css</stylesheet>
+									</attributes>
 								</configuration>
 							</execution>
 							<execution>
@@ -272,11 +315,12 @@
 								</goals>
 								<configuration>
 									<backend>pdf</backend>
+									<outputDirectory>${project.build.directory}/generated-docs/reference/pdf</outputDirectory>
 								</configuration>
 							</execution>
 						</executions>
 						<configuration>
-							<sourceDocumentName>index.adoc</sourceDocumentName>
+							<sourceDirectory>${refdocs.build.directory}</sourceDirectory>
 							<attributes>
 								<github-tag>${github-tag}</github-tag>
 								<version-type>${version-type}</version-type>

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/asciidoc/css/style.css

@@ -0,0 +1,20 @@
+@import url("spring.css");
+
+div .switch {
+    margin-left: 8px;
+    border-color: #406A2A;
+    border-radius: 4px 4px 0 0;
+}
+
+div .switch--item {
+    color: #406A2A;
+    background-color: transparent;
+}
+
+div .switch--item.selected {
+    background-color: #406A2A;
+}
+
+div .switch--item:not(:first-child) {
+    border-color: #406A2A;
+}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/asciidoc/index.adoc

@@ -7,6 +7,8 @@ Andy Wilkinson
 :numbered:
 :icons: font
 :hide-uri-scheme:
+:docinfo: shared,private
+
 :dependency-management-plugin: https://github.com/spring-gradle-plugins/dependency-management-plugin
 :dependency-management-plugin-documentation: {dependency-management-plugin}/blob/master/README.md
 :gradle-userguide: https://docs.gradle.org/current/userguide
@@ -30,7 +32,6 @@ Andy Wilkinson
 :github-code: https://github.com/spring-projects/spring-boot/tree/{github-tag}
 
 
-
 [[introduction]]
 == Introduction