Include Kotlin API documentation in the documentation site

Closes gh-40692

buildSrc/build.gradle

@@ -41,6 +41,7 @@ dependencies {
 
 	implementation(platform("org.springframework:spring-framework-bom:${versions.springFramework}"))
 	implementation("com.diffplug.gradle:goomph:3.37.2")
+	implementation("dev.adamko.dokkatoo:dokkatoo-plugin:2.3.1")
 	implementation("com.fasterxml.jackson.core:jackson-databind:${versions.jackson}")
 	implementation("com.github.node-gradle:gradle-node-plugin:3.5.1")
 	implementation("com.gradle:develocity-gradle-plugin:3.17.2")

buildSrc/src/main/java/org/springframework/boot/build/JavaConventions.java

@@ -261,8 +261,9 @@ class JavaConventions {
 			configuration.setCanBeResolved(false);
 		});
 		configurations
-			.matching((configuration) -> configuration.getName().endsWith("Classpath")
+			.matching((configuration) -> (configuration.getName().endsWith("Classpath")
 					|| JavaPlugin.ANNOTATION_PROCESSOR_CONFIGURATION_NAME.equals(configuration.getName()))
+					&& (!configuration.getName().contains("dokkatoo")))
 			.all((configuration) -> configuration.extendsFrom(dependencyManagement));
 		Dependency springBootParent = project.getDependencies()
 			.enforcedPlatform(project.getDependencies()

buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -19,7 +19,10 @@ package org.springframework.boot.build;
 import java.util.ArrayList;
 import java.util.List;
 
+import dev.adamko.dokkatoo.DokkatooExtension;
+import dev.adamko.dokkatoo.formats.DokkatooHtmlPlugin;
 import org.gradle.api.Project;
+import org.gradle.api.tasks.SourceSet;
 import org.jetbrains.kotlin.gradle.dsl.KotlinJvmOptions;
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile;
 
@@ -44,9 +47,10 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile;
 class KotlinConventions {
 
 	void apply(Project project) {
-		project.getPlugins()
-			.withId("org.jetbrains.kotlin.jvm",
-					(plugin) -> project.getTasks().withType(KotlinCompile.class, this::configure));
+		project.getPlugins().withId("org.jetbrains.kotlin.jvm", (plugin) -> {
+			project.getTasks().withType(KotlinCompile.class, this::configure);
+			configureDokkatoo(project);
+		});
 	}
 
 	private void configure(KotlinCompile compile) {
@@ -60,4 +64,12 @@ class KotlinConventions {
 		compile.getKotlinOptions().setFreeCompilerArgs(freeCompilerArgs);
 	}
 
+	private void configureDokkatoo(Project project) {
+		project.getPlugins().apply(DokkatooHtmlPlugin.class);
+		DokkatooExtension dokkatoo = project.getExtensions().getByType(DokkatooExtension.class);
+		dokkatoo.getDokkatooSourceSets()
+			.named(SourceSet.MAIN_SOURCE_SET_NAME)
+			.configure((spec) -> spec.getSourceRoots().setFrom(project.file("src/main/kotlin")));
+	}
+
 }

spring-boot-project/spring-boot-autoconfigure/build.gradle

@@ -1,6 +1,5 @@
 plugins {
 	id "java-library"
-	id "org.jetbrains.kotlin.jvm"
 	id "org.springframework.boot.auto-configuration"
 	id "org.springframework.boot.configuration-properties"
 	id "org.springframework.boot.conventions"

spring-boot-project/spring-boot-docs/build.gradle

@@ -54,6 +54,9 @@ dependencies {
 	configurationProperties(project(path: ":spring-boot-project:spring-boot-test-autoconfigure", configuration: "configurationPropertiesMetadata"))
 	configurationProperties(project(path: ":spring-boot-project:spring-boot-testcontainers", configuration: "configurationPropertiesMetadata"))
 
+	dokkatoo(project(path: ":spring-boot-project:spring-boot"))
+	dokkatoo(project(path: ":spring-boot-project:spring-boot-test"))
+
 	implementation(project(path: ":spring-boot-project:spring-boot-actuator"))
 	implementation(project(path: ":spring-boot-project:spring-boot-actuator-autoconfigure"))
 	implementation(project(path: ":spring-boot-project:spring-boot-autoconfigure"))
@@ -183,6 +186,10 @@ dependencies {
 	testSlices(project(path: ":spring-boot-project:spring-boot-test-autoconfigure", configuration: "testSliceMetadata"))
 }
 
+dokkatoo {
+	moduleName.set("Spring Boot Kotlin API")
+}
+
 task aggregatedJavadoc(type: Javadoc) {
 	dependsOn dependencyVersions
 	project.rootProject.gradle.projectsEvaluated {
@@ -344,6 +351,9 @@ def antoraApiCatalogContent = tasks.register("antoraApiCatalogContent", Zip) {
 	from(aggregatedJavadoc) {
 		into "java"
 	}
+	from(tasks.named("dokkatooGeneratePublicationHtml")) {
+		into "kotlin"
+	}
 }
 
 def copyAntoraContentDependencies = tasks.register("copyAntoraContentDependencies", Copy) {
@@ -366,6 +376,12 @@ gradle.projectsEvaluated {
 	}
 }
 
+dokkatoo {
+	dokkatooPublications.configureEach {
+		includes.from("src/docs/dokkatoo/dokka-overview.md")
+	}
+}
+
 publishing {
 	publications {
 		getByName("maven") {

spring-boot-project/spring-boot-docs/src/docs/antora/antora.yml

@@ -28,3 +28,5 @@ ext:
     attributes: { external: true}
   - path: [ "Java APIs", "Gradle Plugin" ]
     attributes: { external: true }
+  - path: [ "Kotlin APIs", "Spring Boot" ]
+    attributes: { external: true }

spring-boot-project/spring-boot-docs/src/docs/antora/modules/api/partials/nav-kotlin-api.adoc

@@ -0,0 +1,2 @@
+* Kotlin APIs
+** xref:api:kotlin/index.html[Spring Boot]

spring-boot-project/spring-boot-docs/src/docs/antora/nav.adoc

@@ -6,5 +6,6 @@ include::build-tool-plugin:partial$nav-build-tool-plugin.adoc[]
 include::cli:partial$nav-cli.adoc[]
 include::api:partial$nav-rest-api.adoc[]
 include::api:partial$nav-java-api.adoc[]
+include::api:partial$nav-kotlin-api.adoc[]
 include::specification:partial$nav-specification.adoc[]
 include::appendix:partial$nav-appendix.adoc[]

spring-boot-project/spring-boot-docs/src/docs/dokkatoo/dokka-overview.md

@@ -0,0 +1,2 @@
+# All Modules
+_See also the <a href="../java/index.html" target="_blank">Java API documentation (Javadoc)</a>._