basic gradle plugin writing

Gr8Day Warsaw 2016

IDIOMATIC GRADLE

PLUGIN WRITINGSchalk W. Cronjé

ABOUT ME

Email:

Twitter / Ello : @ysb33r

ysb33r@gmail.com

Gradle plugins authored/contributed to: VFS, Asciidoctor,JRuby family (base, jar, war etc.), GnuMake, Doxygen, Bintray

ABOUT THIS PRESENTATIONWritten in Asciidoctor (1.5.3.2)

Styled by asciidoctor-revealjs extension

Built using:

Gradle

gradle-asciidoctor-plugin

gradle-vfs-plugin

GET YOUR DAILY GRADLE DOSE

@DailyGradle

#gradleTip

THE PROBLEMThere is no consistency in the way plugin authors craft extensions

to the Gradle DSL today

QUALITY ATTRIBUTES OF DSL

Readability

Consistency

Flexibility

Expressiveness

PROJECT LAYOUT

Figure 1. Plugin project file layout

BUILD SCRIPTrepositories { jcenter() }

apply plugin : 'groovy'

dependencies { compile localGroovy() compile gradleApi() testCompile ("org.spockframework:spock-core:1.0-groovy-2.3") { exclude module : 'groovy-all' } }

TRICK : SPOCK VERSIONext { spockGrVer = GroovySystem.version.replaceAll(/\.\d+$/,'') }

dependencies { testCompile ("org.spockframework:spock-core:1.0-${spockGrVer}") { exclude module : 'groovy-all' } }

CREATE PLUGIN CLASSpackage idiomatic.gradle.authoring

import org.gradle.api.Plugin import org.gradle.api.Project

class MyExamplePlugin implements Plugin<Project> {

void apply(Project project) { } }

CREATE PROPERTIES FILE

META-INF/gradle-plugins/idiomatic.authored.example.properties

implementation-class=idiomatic.gradle.authoring.MyExamplePlugin

Name of file must match plugin identifier

CREATE TASK CLASSpackage idiomatic.gradle.authoring

import org.gradle.api.DefaultTask import org.gradle.api.tasks.TaskAction

class MyExampleTasks extends DefaultTask {

@TaskAction void exec() { } }

FOR BEST COMPATIBILITY

Support same JDK range as Gradle

Gradle 1.x - mininum JDK5

Gradle 2.x - minimum JDK6

Build against Gradle 2.0

Only use later versions if specific new functionality is

required.

Suggested baseline at Gradle 2.10 (for new model)

JDK COMPATIBILITY// build.gradle targetCompatibility = 1.6 sourceCompatibility = 1.6

project.tasks.withType(JavaCompile) { task -> task.sourceCompatibility = project.sourceCompatibility task.targetCompatibility = project.targetCompatibility }

project.tasks.withType(GroovyCompile) { task -> task.sourceCompatibility = project.sourceCompatibility task.targetCompatibility = project.targetCompatibility }

GRADLE BUILD VERSION// gradle/wrapper/gradle-wrapper.properties distributionUrl=https\://..../distributions/gradle-2.0-all.zip

HONOUR OFFLINEgradle --offline

The build should operate without accessingnetwork resources.

HONOUR OFFLINEUnset the enabled property, if build is offline

task VfsCopy extends DefaultTask { VfsCopy() {

enabled = !project.gradle.startParameter.isOffline()

}

}

PREFER METHODS OVER PROPERTIES( IOW To assign or not to assign )

Methods provide more flexibility

Tend to provide better readability

Assignment is better suited towards

One-shot attribute setting

Overriding default attributes

Non-lazy evaluation

HOW NOT 2 : COLLECTION OF FILESTypical implementation …

class MyTask extends DefaultTask {

@InputFiles List<File> mySources

}

leads to ugly DSL

task myTask( type: MyTask ) {

myTask = [ file('foo/bar.txt'), new File( 'bar/foo.txt') ]

}

COLLECTION OF FILESmyTask { mySources file( 'path/foobar' ) mySources new File( 'path2/foobar' ) mySources 'file3', 'file4' mySources { "lazy evaluate file name later on" } }

Allow ability to:

Use strings and other objects convertible to File

Append lists

Evaluate as late as possible

Reset default values

COLLECTION OF FILES

Ignore Groovy shortcut; use three methods

class MyTask extends DefaultTask { @InputFiles

FileCollection getDocuments() {

project.files(this.documents) // magic API method }

void setDocuments(Object... docs) { this.documents.clear()

this.documents.addAll(docs as List) }

void documents(Object... docs) { this.documents.addAll(docs as List) }

private List<Object> documents = [] }

STYLE : TASKSProvide a default instantiation of your new task class

Keep in mind that user would want to create additionaltasks of same type

Make it easy for them!!

KNOW YOUR ANNOTATIONS

@Input

@InputFile

@InputFiles

@InputDirectory

@OutputFile

@OutputFiles

@OutputDirectory

@OutputDirectories

@Optional

COLLECTION OF STRINGSimport org.gradle.util.CollectionUtils

Ignore Groovy shortcut; use three methods

@Input

List<String> getScriptArgs() {

// stringize() is your next magic API method CollectionUtils.stringize(this.scriptArgs)

}

void setScriptArgs(Object... args) { this.scriptArgs.clear()

this.scriptArgs.addAll(args as List) }

void scriptArgs(Object... args) { this.scriptArgs.addAll(args as List) }

private List<Object> scriptArgs = []

HOW NOT 2 : MAPSTypical implementation …

class MyTask extends DefaultTask {

@Input

Map myOptions

}

leads to ugly DSL

task myTask( type: MyTask ) {

myOptions = [ prop1 : 'foo/bar.txt', prop2 : 'bar/foo.txt' ]

}

MAPStask myTask( type: MyTask ) {

myOptions prop1 : 'foo/bar.txt', prop2 : 'bar/foo.txt'

myOptions prop3 : 'add/another'

// Explicit reset myOptions = [:]

}

MAPS@Input

Map getMyOptions() {

this.attrs

}

void setMyOptions(Map m) { this.attrs=m

}

void myOptions(Map m) { this.attrs+=m

}

private Map attrs = [:]

COMPATIBILITY TESTING

How can a plugin author test a plugin against multiple Gradle

versions?

COMPATIBILITY TESTING

Gradle 2.7 added TestKit

Gradle 2.9 added multi-distribution testing

TestKit still falls short in ease-of-use

(Hopefully to be corrected over future releases)

What to do for Gradle 2.0 - 2.8?

COMPATIBILITY TESTING

GradleTest plugin to the rescue

buildscript { dependencies { classpath "org.ysb33r.gradle:gradletest:0.5.4" } }

apply plugin : 'org.ysb33r.gradletest'

http://bit.ly/1LfUUU4

COMPATIBILITY TESTING

Create src/gradleTest/NameOfTest folder.

Add build.gradle

Add task runGradleTest

Add project structure

COMPATIBILITY TESTING

Add versions to main build.gradle

gradleTest { versions '2.0', '2.2', '2.4', '2.5', '2.9' }

Run it!

./gradlew gradleTest

THANK YOU

Keep your DSLextensions beautiful

Don’t spring surprisingbehaviour on the user

Email:

Twitter / Ello : @ysb33r

#idiomaticgradle

ysb33r@gmail.com

http://bit.ly/1iJmdiP

ADVANCED CONCEPTS

NOMENCLATURE

Property: A public data member (A Groovy property)

Method: A standard Java/Groovy method

Attribute: A value, set or accessed via the Gradle DSL. Canresult in a public method call or property access.

User: Person authoring or executing a Gradle build script

@Input String aProperty = 'stdValue'

@Input void aValue(String s) { ... }

myTask { aProperty = 'newValue'

aValue 'newValue' }

USER OVERRIDE LIBRARY VERSION

Ship with prefered (and tested) version of dependentlibrary set as default

Allow user flexibility to try a different version of suchlibrary

Dynamically load library when needed

Still use power of Gradle’s dependency resolution

USER OVERRIDE LIBRARY VERSION

Example DSL from Asciidoctor

asciidoctorj { version = '1.6.0-SNAPSHOT' }

Example DSL from JRuby Base

jruby { execVersion = '1.7.12'}

USER OVERRIDE LIBRARY VERSION

1. Create Extension

2. Add extension object in plugin apply

3. Create custom classloader

USER OVERRIDE LIBRARY VERSION

Step 1: Create project extension

class MyExtension {

// Set the default dependent library version String version = '1.5.0'

MyExtension(Project proj) { project= proj }

@PackageScope Project project }

USER OVERRIDE LIBRARY VERSION

Step 2: Add extension object in plugin apply

class MyPlugin implements Plugin<Project> { void apply(Project project) {

// Create the extension & configuration project.extensions.create('asciidoctorj',MyExtension,project) project.configuration.maybeCreate( 'int_asciidoctorj' )

// Add dependency at the end of configuration phase project.afterEvaluate { project.dependencies { int_asciidoctorj "org.asciidoctor:asciidoctorj" + "${project.asciidoctorj.version}" } } } }

USER OVERRIDE LIBRARY VERSION (2.5+)

Step 2: Add extension object Gradle 2.5+

class MyPlugin implements Plugin<Project> { void apply(Project project) {

// Create the extension & configuration project.extensions.create('asciidoctorj',MyExtension,project) def conf = configurations.maybeCreate( 'int_asciidoctorj' )

conf.defaultDependencies { deps -> deps.add( project.dependencies.create( "org.asciidoctor:asciidoctorj:${asciidoctorj.version}") ) } } }

USER OVERRIDE LIBRARY VERSION

Step 3: Custom classloader (usually loaded from task action)

// Get all of the files in the `asciidoctorj` configuration def urls = project.configurations.int_asciidoctorj.files.collect { it.toURI().toURL() }

// Create the classloader for all those files def classLoader = new URLClassLoader(urls as URL[], Thread.currentThread().contextClassLoader)

// Load one or more classes as required def instance = classLoader.loadClass( 'org.asciidoctor.Asciidoctor$Factory')

NEED 2 KNOW : 'AFTEREVALUATE'

afterEvaluate adds to a list of closures to be executed

at end of configuration phase

Execution order is FIFO

Plugin author has no control over the order

STYLE : PROJECT EXTENSIONS

Treat project extensions as you would for any kind ofglobal configuration.

With care!

Do not make the extension configuration block a taskconfiguration.

Task instantiation may read defaults from extension.

Do not force extension values onto tasks

NEED 2 KNOW : PLUGINS

Plugin author has no control over order in which plugins

will be applied

Handle both cases of related plugin applied before or after

yours

EXTEND EXISTING TASKTask type extension by inheritance is not always bestsolution

Adding behaviour to existing task type better in certaincontexts

Example: jruby-jar-plugin wants to semanticallydescribe bootstrap files rather than force user to usestandard Copy syntax

EXTEND EXISTING TASKjruby-jar-plugin without extension

jrubyJavaBootstrap { // User gets exposed (unnecessarily) to the underlying task type // Has to craft too much glue code from( { // @#$$!!-ugly code goes here } ) }

jruby-jar-plugin with extension

jrubyJavaBootstrap { // Expressing intent & context. jruby { initScript = 'bin/asciidoctor' } }

EXTEND EXISTING TASK1. Create extension class

2. Add extension to task

3. Link extension attributes to task attributes (for caching)

EXTEND EXISTING TASKCreate extension class

class MyExtension { String initScript

MyExtension( Task t ) {

// TODO: Add Gradle caching support // (See later slide) }

}

EXTEND EXISTING TASKAdd extension class to task

class MyPlugin implements Plugin<Project> { void apply(Project project) { Task stubTask = project.tasks.create ( name : 'jrubyJavaBootstrap', type : Copy )

stubTask.extensions.create( 'jruby', MyExtension, stubTask ) }

EXTEND EXISTING TASKAdd Gradle caching support

class MyExtension { String initScript

MyExtension( Task t ) {

// Tell the task the initScript is also a property t.inputs.property 'jrubyInitScript' , { -> this.initScript } } }

NEED 2 KNOW : TASK EXTENSIONS

Good way extend existing tasks in composable way

Attributes on extensions are not cached

Changes will not cause a rebuild of the task

Do the extra work to cache and provide the user with abetter experience.

ADD GENERATED JVM SOURCE SETS

May need to generate code from template and add to

current sourceset(s)

Example: Older versions of jruby-jar-plugin added

a custom class file to JAR

Useful for separation of concerns in certain generative

programming environments

ADD GENERATED JVM SOURCE SETS

1. Create generator task using Copy task as transformer

2. Configure generator task

3. Update SourceSet

4. Add dependency between generation and compilation

ADD GENERATED JVM SOURCE SETS

Step1 : Add generator task

class MyPlugin implements Plugin<Project> { void apply(Project project) { Task stubTask = project.tasks.create ( name : 'myGenerator', type : Copy )

configureGenerator(stubTask) addGeneratedToSource(project) addTaskDependencies(project) }

void configureGenerator(Task t) { /* TODO: <-- See next slides */ } void addGeneratedToSource(Project p) { /* TODO: <-- See next slides */ } void addTaskDependencies(Project p) { /* TODO: <-- See next slides */ } }

This example uses Java, but can apply to any kind of sourcesetthat Gradle supports

ADD GENERATED JVM SOURCE SETS

Step 2 : Configure generator task

/* DONE: <-- See previous slide for apply() */ void configureGenerator(Task stubTask) { project.configure(stubTask) { group "Add to correct group" description 'Generates a JRuby Java bootstrap class'

from('src/template/java') { include '*.java.template' } into new File(project.buildDir,'generated/java')

rename '(.+)\\.java\\.template','$1.java' filter { String line -> /* Do something in here to transform the code */ } } }

ADD GENERATED JVM SOURCE SETS

Step 3 : Add generated code to SourceSet

/* DONE: <-- See earlier slide for apply() */

void addGeneratedToSource(Project project) {

project.sourceSets.matching { it.name == "main" } .all { it.java.srcDir new File(project.buildDir,'generated/java') }

}

ADD GENERATED JVM SOURCE SETS

Step 4 : Add task dependencies

/* DONE: <-- See earlier slide for apply() */

void addTaskDependencies(Project project) { try { Task t = project.tasks.getByName('compileJava')

if( t instanceof JavaCompile) { t.dependsOn 'myGenerator'

}

} catch(UnknownTaskException) { project.tasks.whenTaskAdded { Task t ->

if (t.name == 'compileJava' && t instanceof JavaCompile) { t.dependsOn 'myGenerator'

}

}

}

}

TRICK : SAFE FILENAMESAbility to create safe filenames on all platforms from inputdata

Example: Asciidoctor output directories based uponbackend names

// WARNING: Using a very useful internal API import org.gradle.internal.FileUtils

File outputBackendDir(final File outputDir, final String backend) { // FileUtils.toSafeFileName is your magic method new File(outputDir, FileUtils.toSafeFileName(backend)) }

TRICK : SELF-REFERENCING PLUGINNew plugin depends on functionality in the plugin

Apply plugin direct in build.gradle

apply plugin: new GroovyScriptEngine( ['src/main/groovy','src/main/resources']. collect{ file(it).absolutePath } .toArray(new String[2]), project.class.classLoader ).loadScriptByName('book/SelfReferencingPlugin.groovy')

TRICK : OPERATING SYSTEM

Sometimes customised work has to be done on a specific

O/S

Example: jruby-gradle-plugin needs to set TMP in

environment on Windows

// This is the public interface API import org.gradle.nativeplatform.platform.OperatingSystem

// But to get an instance the internal API is needed instead import org.gradle.internal.os.OperatingSystem

println "Are we on Windows? ${OperatingSystem.current().isWindows()}

THANK YOU

Keep your DSLextensions beautiful

Don’t spring surprisingbehaviour on the user

Email:

Twitter / Ello : @ysb33r

#idiomaticgradle

ysb33r@gmail.com

http://bit.ly/1iJmdiP