How to write Gradle Plugins in Kotlin

Given at Droidcon Italy 2018

Every Android Developer is familiar with Gradle, right?
We know how to apply a plugin, how to setup the Android extension and how to declare our dependencies.

But from where does the Android extension come from?
Which settings are possible here?
How can a task use these information to run a specific action?

I'll explain all the Gradle magic by showing how to write a Gradle plugin.
The plugin will be pretty simple and straightforward but shows you what Gradle does behind the scenes.

Naturally we will write the plugin in Kotlin.
We will also cover a little bit about Gradle's Kotlin DSL.

Basically you will leave my talk knowing the basics of the Gradle plugin development:
* How can I declare my own task?
* How can I declare my own extension?
* How can I test my plugin?

Transcript

1. How to write Gradle plugins in Kotlin 1 / 42
2. plugins { id("person-creater") version "26" } person { create("stefan") { name = "Stefan" lastName = "May" country = "Germany" avatar = "https://goo.gl/BV2a67" jobTitle = "Android Developer" workingSince = "07/2014" company { name = "grandcentrix" location = "Cologne" 2 / 42
3. lastName = "May" country = "Germany" avatar = "https://goo.gl/BV2a67" jobTitle = "Android Developer" workingSince = "07/2014" company { name = "grandcentrix" location = "Cologne" remoteWorker = true } social { twitter = "@StefMa91" github = "StefMa" medium = "@StefMa" } } } 2 / 42
4. • Why? • The Project: Gloc (Gradle Lines Of Code) • How to write a Plugin 3 / 42
5. • Android Developer since July 2014 • Android Studio stable December 2014 together with the Gradle Plugin Gradle… what is Gradle? • Copy & Paste from stackoverflow • The raise of build variants & product flavors • Raise of plugins… 5 / 42
6. • Android Developer since July 2014 • Android Studio stable December 2014 together with the Gradle Plugin Gradle… what is Gradle? • Copy & Paste from stackoverflow • The raise of build variants & product flavors • Raise of plugins… WHAT IS GRADLE!!!111!1oneeleven 5 / 42
7. • Why? • The Project: Gloc (Gradle Lines Of Code) • How to write a Plugin 6 / 42
8. plugins { id("guru.stefma.gloc") version "0.0.1" } gloc { enabled = true dirs = arrayOf("src/main", "src/test") } 7 / 42
9. ./gradlew gloc --console=plain Hello Plugin \o/ :glocInput :gloc Output can be found at /Users/stefan/Developer/DroidconItaly/Gloc/gloc/build/gloc/gloc.txt BUILD SUCCESSFUL in 0s 2 actionable tasks: 2 executed 8 / 42
10. BUILD SUCCESSFUL in 0s 2 actionable tasks: 2 executed ./gradlew gloc --console=plain Hello Plugin \o/ :glocInput :gloc UP-TO-DATE BUILD SUCCESSFUL in 0s 2 actionable tasks: 1 executed, 1 up-to-date 8 / 42
11. 2 actionable tasks: 1 executed, 1 up-to-date ./gradlew clean gloc --build-cache --console=plain Hello Plugin \o/ :clean :glocInput :gloc Output can be found at /Users/stefan/Developer/DroidconItaly/Gloc/gloc/build/gloc/gloc.txt BUILD SUCCESSFUL in 0s 3 actionable tasks: 3 executed 8 / 42
12. BUILD SUCCESSFUL in 0s 3 actionable tasks: 3 executed ./gradlew clean gloc --build-cache --console=plain Hello Plugin \o/ :clean :glocInput :gloc FROM-CACHE BUILD SUCCESSFUL in 0s 3 actionable tasks: 2 executed, 1 from cache 8 / 42
13. cat /Users/stefan/Developer/DroidconItaly/Gloc/gloc/build/gloc/gloc.txt Directory 'main': 'kt' has '145' LOC in sum Directory 'test': 'kt' has '413' LOC in sum 9 / 42
14. • Why? • The Project: Gloc • How to write a Plugin 10 / 42
15.  gradle
     wrapper
     gradle-wrapper.jar
     gradle-wrapper.properties  gradlew  gradlew.bat   build.gradle.kts  settings.gradle.kts   src  main
     kotlin
     guru.stefma.gloc  test 11 / 42
16.  gradle
     wrapper
     gradle-wrapper.jar
     gradle-wrapper.properties  gradlew  gradlew.bat   build.gradle.kts  settings.gradle.kts   src  main
     kotlin
     guru.stefma.gloc  test  kotlin  guru.stefma.gloc 11 / 42
17. plugins { kotlin("jvm") version ("1.2.30") id("java-gradle-plugin") id("maven-publish") } 12 / 42
18. lugins { kotlin("jvm") version ("1.2.30") id("java-gradle-plugin") id("maven-publish") • applies java plugin • gradleApi() dependency • gradleTestKit() dependency 13 / 42
19. plugins { kotlin("jvm") version ("1.2.30") id("java-gradle-plugin") id("maven-publish") } repositories { 14 / 42
20. } repositories { jcenter() } dependencies { implementation(kotlin("stdlib-jdk8")) testImplementation("org.assertj:assertj-core:3.9.0") testImplementation("org.junit.jupiter:junit-jupiter-api:5.1.0") testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.1.0") } 14 / 42
21. testImplementation("org.junit.jupiter:junit-jupiter-api:5.1.0") testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.1.0") } (tasks.findByName("test") as Test).useJUnitPlatform() group = "guru.stefma.gloc" version = "0.0.1" gradlePlugin { plugins { create("gloc") { id = "guru.stefma.gloc" implementationClass = "guru.stefma.gloc.GlocPlugin" } } } 14 / 42
22. open class GlocPlugin : Plugin<Project> { override fun apply(project: Project) { println("Hello Plugin \\o/") } } 15 / 42
23. val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("tasks") .build() 16 / 42
24. File(tempDir, "build.gradle").run { writeText(""" plugins { id "guru.stefma.gloc" } """) } val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .build() assertThat(buildResult.output).contains("Hello Plugin \\o/") 17 / 42
25. open class GlocExtension { var enabled: Boolean = true var dirs: Array<String> = emptyArray() } 18 / 42
26. override fun apply(project: Project) { println("Hello Plugin \\o/") val extension = project.extensions.run { create("gloc", GlocExtension::class.java) } } 19 / 42
27. override fun apply(project: Project) { val extension = project.extensions.run { create("gloc", GlocExtension::class.java) } project.afterEvaluate { if (!extension.enabled) return@afterEvaluate println("Hello Plugin \\o/") } } 20 / 42
28. fun `apply and enabled false should not print hello plugin`(tempDir: File) { File(tempDir, "build.gradle").run { writeText(""" plugins { id "guru.stefma.gloc" } gloc { enabled = false } """) } val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() 21 / 42
29. File(tempDir, "build.gradle").run { writeText(""" plugins { id "guru.stefma.gloc" } gloc { enabled = false } """) } val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .build() assertThat(buildResult.output).doesNotContain("Hello Plugin \\o/") } 21 / 42
30. plugins { id "guru.stefma.gloc" } gloc { enabled = false enabled = true } """) } val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .build() assertThat(buildResult.output).doesNotContain("Hello Plugin \\o/") assertThat(buildResult.output).contain(„Hello Plugin \\o/") } 22 / 42
31. plugins { id("guru.stefma.gloc") version "0.0.1" } gloc { enabled = true dirs = arrayOf("src/main", "src/test") } 23 / 42
32. open class GlocTask : DefaultTask() { @TaskAction fun action() { println("Hello from Task") } } 24 / 42
33. override fun apply(project: Project) { ... val glocTask = with(project.tasks) { create("gloc", GlocTask::class.java) { it.group = "Development" it.description = "Get the lines of code for files" } } } 25 / 42
34. File(tempDir, "build.gradle").run { writeText( """ plugins { id("guru.stefma.gloc") } """ ) } val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() 26 / 42
35. """ plugins { id("guru.stefma.gloc") } """ ) } val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() assertThat(buildResult.output).contains("Hello from Task") assertThat(buildResult.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) 26 / 42
36. val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() val buildResult2 = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() assertThat(buildResult.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) assertThat(buildResult2.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.UP_TO_DATE) 27 / 42
37. val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() val buildResult2 = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() assertThat(buildResult.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) assertThat(buildResult2.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.UP_TO_DATE) ❌ 27 / 42
38. open class GlocTask : DefaultTask() { @OutputFile var output = project.file("${project.buildDir}/gloc/gloc.txt") @TaskAction fun action() { output.createNewFile() output.writeText("Hello World") } } 28 / 42
39. val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() val buildResult2 = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() assertThat(buildResult.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) assertThat(buildResult2.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.UP_TO_DATE) 29 / 42
40. val buildResult = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() val buildResult2 = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() assertThat(buildResult.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) assertThat(buildResult2.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.UP_TO_DATE) ✅ 29 / 42
41. open class GlocTask : DefaultTask() { @OutputFile var output = project.file("${project.buildDir}/gloc/gloc.txt") @TaskAction fun action() { val extension = project.extensions.run { findByName("gloc") as GlocExtension } if (extension.enabled) { createPrettyOutputFile(extensions.dirs) println("Output can be found at ${output.absolutePath}") } 30 / 42
42. open class GlocTask : DefaultTask() { @OutputFile var output = project.file("${project.buildDir}/gloc/gloc.txt") @TaskAction fun action() { val extension = project.extensions.run { findByName("gloc") as GlocExtension } if (extension.enabled) { createPrettyOutputFile(extensions.dirs) println("Output can be found at ${output.absolutePath}") } } } 30 / 42
43. fun `task should read test xml file and should write loc in it`(tempDir: File) { File(tempDir, "build.gradle").run { writeText( """ plugins { id "guru.stefma.gloc" } gloc { enabled = true dirs = [projectDir.path + "/source"] } """ ) } 31 / 42
44. enabled = true dirs = [projectDir.path + "/source"] } """ ) } File(tempDir, "source/test.xml").apply { parentFile.mkdirs() createNewFile() writeText("This\nis\ndroidcon\nitaly\nturin") } GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() 31 / 42
45. ) } File(tempDir, "source/test.xml").apply { parentFile.mkdirs() createNewFile() writeText("This\nis\ndroidcon\nitaly\nturin") } GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc") .build() val glocFileText = File(tempDir, "build/gloc/gloc.txt") assertThat(glocFileText.readText()).contains("5") } 31 / 42
46. @Test fun `task run twice with different dirs should be run twice`(tempDir: File) { runTest(tempDir, "source") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } runTest(tempDir, "anotherSource") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } } 32 / 42
47. @Test fun `task run twice with different dirs should be run twice`(tempDir: File) { runTest(tempDir, "source") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } runTest(tempDir, "anotherSource") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } } ❌ 32 / 42
48. @Test fun `task run twice with different dirs should be run twice`(tempDir: File) { runTest(tempDir, "source") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } runTest(tempDir, "anotherSource") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) TaskOutcome.UP_TO_DATE } } # 33 / 42
49. open class GlocTask : DefaultTask() { @OutputFile var output = project.file("${project.buildDir}/gloc/gloc.txt") @Input var inputDirs = (project.extensions.findByName("gloc") as GlocExtension) .dirs.run { map { it }.toString() } ... } 34 / 42
50. open class GlocTask : DefaultTask() { ... @Input var inputDirs = (project.extensions.findByName("gloc") as GlocExtension) .dirs.run { map { it }.toString() } @InputFile var inputDirs = project.file("${project.buildDir}/gloc/inputdirs.txt") ... } 35 / 42
51. open class GlocInputTask : DefaultTask() { @TaskAction fun writeInput() { val filePath = "{project.buildDir}/gloc/inputdirs.txt" val inputFile = project.file("$filePath").apply { parentFile.mkdirs() createNewFile() writeText("") } (project.extensions.findByName("gloc") as GlocExtension) .dirs.forEach { inputFile.appendText(it) } } } 36 / 42
52. override fun apply(project: Project) { val inputTask = project.tasks.run { create("glocInput", GlocInputTask::class.java) } with(project.tasks) { create("gloc", GlocTask::class.java) { it.group = "Development" it.description = "Get the lines of code for files" it.dependsOn(inputTask) } } } 37 / 42
53. @Test fun `task run twice with different dirs should be run twice`(tempDir: File) { runTest(tempDir, "source") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } runTest(tempDir, "anotherSource") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } } 38 / 42
54. @Test fun `task run twice with different dirs should be run twice`(tempDir: File) { runTest(tempDir, "source") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } runTest(tempDir, "anotherSource") { assertThat(it.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) } } ✅ 38 / 42
55. open class GlocTask : DefaultTask() { @OutputFile ... @InputFile ... @TaskAction ... } 39 / 42
56. open class GlocTask : DefaultTask() { @OutputFile ... @InputFile ... @TaskAction ... } @CacheableTask 39 / 42
57. fun `task should read from build cache`(tempDir: File) { File(tempDir, "build.gradle").run { writeText( """ plugins { id "guru.stefma.gloc" } gloc { enabled = true dirs = [projectDir.path + "/source"] } """ ) } 40 / 42
58. plugins { id "guru.stefma.gloc" } gloc { enabled = true dirs = [projectDir.path + "/source"] } """ ) } File(tempDir, "source/test.xml").apply { parentFile.mkdirs() createNewFile() writeText("This\nis\droidcon\nitaly\nturin") } 40 / 42
59. createNewFile() writeText("This\nis\droidcon\nitaly\nturin") } File(tempDir, "settings.gradle").run { writeText( """ buildCache { local { directory = "$tempDir/cache" } } """ ) } val build = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc", "--build-cache") .build() 40 / 42
60. } val build = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc", "--build-cache") .build() assertThat(build.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) // Clean build dir and run again - should be read from build cache File(tempDir, "build/").deleteRecursively() val build2 = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc", "--build-cache") .build() 40 / 42
61. .withPluginClasspath() .withArguments("gloc", "--build-cache") .build() assertThat(build.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.SUCCESS) // Clean build dir and run again - should be read from build cache File(tempDir, "build/").deleteRecursively() val build2 = GradleRunner.create() .withProjectDir(tempDir) .withPluginClasspath() .withArguments("gloc", "--build-cache") .build() assertThat(build2.task(":gloc")!!.outcome) .isEqualTo(TaskOutcome.FROM_CACHE) } 40 / 42
62. 41 / 42
63. • Created the project 42 / 42
64. • Created the project • Created the gradle files and registered the plugin 42 / 42
65. • Created the project • Created the gradle files and registered the plugin gradlePlugin { plugins { create("gloc") { id = "guru.stefma.gloc" implementationClass = "guru.stefma.gloc.GlocPlugin" } } } 42 / 42
66. • Created the project • Created the plugin • Created the gradle files and registered the plugin 42 / 42
67. • Created the project • Created the plugin • Created the gradle files and registered the plugin open class GlocPlugin : Plugin<Project> { override fun apply(project: Project) { project.extensions.create(...) project.tasks.create(...) } } 42 / 42
68. • Created the project • Created the plugin • Created the extension • Created the gradle files and registered the plugin 42 / 42
69. • Created the project • Created the plugin • Created the extension • Created the gradle files and registered the plugin open class GlocExtension { var enabled: Boolean = true var dirs: Array<String> = emptyArray() } 42 / 42
70. • Created the project • Created the plugin • Created the extension • Created the task • Created the gradle files and registered the plugin 42 / 42
71. • Created the project • Created the plugin • Created the extension • Created the task • Created the gradle files and registered the plugin @CacheableTask open class GlocTask : DefaultTask() { @OutputFile ... @InputFile ... @Action ... } 42 / 42
72. plugins { id("gradle-plugin-how-to") version "0.1-ALPHA" } about { name = "Stefan May“ twitter = "https://twitter.com/@StefMa91" medium = "https://medium.com/@StefMa" } code { availableAt = "https://github.com/StefMa/Gloc" } 43