Add API and reference documentation for Kotlin support

Issue: SPR-15659

Author: sdeleuze

build.gradle

@@ -15,6 +15,7 @@ plugins {
 	id "com.gradle.build-scan" version "1.8"
 	id "io.spring.dependency-management" version "1.0.3.RELEASE" apply false
 	id "org.jetbrains.kotlin.jvm" version "1.1.4" apply false
+	id "org.jetbrains.dokka" version "0.9.15"
 	id "org.asciidoctor.convert" version "1.5.3"
 }
 

gradle/docs.gradle

@@ -49,6 +49,36 @@ task api(type: Javadoc) {
 	}
 }
 
+// Need https://github.com/Kotlin/dokka/issues/184 to be fixed to avoid "Can't find node by signature" log spam
+dokka {
+	dependsOn {
+		subprojects.collect {
+			it.tasks.getByName("jar")
+		}
+	}
+	doFirst {
+		classpath = subprojects.collect { project -> project.jar.outputs.files.getFiles() }.flatten()
+		classpath += files(subprojects.collect { it.sourceSets.main.compileClasspath })
+
+	}
+	moduleName = "spring-framework"
+	outputFormat = "html"
+	outputDirectory = "$buildDir/docs/kdoc"
+
+	sourceDirs = files(subprojects.collect { project ->
+		project.sourceSets.main.kotlin.srcDirs
+	})
+	externalDocumentationLink {
+		url = new URL("http://docs.spring.io/spring-framework/docs/${version}/javadoc-api/")
+	}
+	externalDocumentationLink {
+		url = new URL("http://projectreactor.io/docs/core/release/api/")
+	}
+	externalDocumentationLink {
+		url = new URL("http://www.reactive-streams.org/reactive-streams-1.0.1-javadoc/")
+	}
+}
+
 asciidoctor {
 	sources {
 		include '*.adoc'
@@ -74,7 +104,7 @@ asciidoctor {
 
 }
 
-task docsZip(type: Zip, dependsOn: ['api', 'asciidoctor']) {
+task docsZip(type: Zip, dependsOn: ['api', 'asciidoctor', 'dokka']) {
 	group = "Distribution"
 	baseName = "spring-framework"
 	classifier = "docs"
@@ -92,6 +122,10 @@ task docsZip(type: Zip, dependsOn: ['api', 'asciidoctor']) {
 	from (asciidoctor) {
 		into "spring-framework-reference"
 	}
+
+	from (dokka) {
+		into "kdoc-api"
+	}
 }
 
 task schemaZip(type: Zip) {

src/docs/asciidoc/index.adoc

@@ -33,6 +33,8 @@ This reference document provides the following sections:
  ** <<web.adoc#spring-web,Servlet-based stack with Spring MVC>>
  ** <<reactive-web.adoc#spring-webflux, Reactive stack with Spring WebFlux>>
 
+* <<kotlin.adoc#kotlin,Kotlin support>>
+
 * <<integration.adoc#spring-integration,Integration with other technologies>>
 
 * <<appendix.adoc#spring-appendices,Appendix>>