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Develop your CI Tools

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Xavier F. Gouchet Senior Software Engineer at Datadog @xgouchet / @datadoghq

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0. Introduction

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Small team ▫ 3 engineers ▫ Lots of features ▫ Lots of bug fixes ▫ Lots of improvements ▫ Small bandwidth Unsplash photo by @marvelous

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CI setup ▫ Gitlab ▫ Bitrise * photo by @xgouchet

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Delegating to the CI ▫ Runs automatically ▫ Strict and thorough ▫ Great way to offload the PR Review

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Code Review Pyramid Credit: Gunnar Morling (CC-BY-SA 4.0) CODE STYLE TESTS IMPLEMENTATION API SEMANTICS DOCUMENTATION

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1. Detekt Your code, your rules…

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What is Detekt? ▫ Kotlin Static Analysis ▫ Code smells ▫ Performance Issues ▫ Code complexity ▫ Documentation Missing ▫ …

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Detekt Report

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How does Detekt work ▫ Visitor pattern over the Syntax Tree (PSI) ▫ With Type Resolution ▫ Report issues on specific patterns

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Custom Rule class MyCustomRule : Rule() { override val issue: Issue = Issue( javaClass.simpleName, Severity.CodeSmell, "A description of the issue…", Debt.TWENTY_MINS ) }

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Custom Rule class MyCustomRule : Rule() { override val issue: Issue = Issue( javaClass.simpleName, Severity.CodeSmell, "A description of the issue…", Debt.TWENTY_MINS ) }

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Custom Rule class MyCustomRule : Rule() { override val issue: Issue = Issue( javaClass.simpleName, Severity.CodeSmell, "A description of the issue…", Debt.TWENTY_MINS ) }

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Custom Rule override fun visitExpression(expression: KtExpression) { if (invalidExpression(expression)) report( CodeSmell( issue, Entity.from(expression), "A message" ) ) }

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Custom Rule override fun visitExpression(expression: KtExpression) { if (invalidExpression(expression)) report( CodeSmell( issue, Entity.from(expression), "A message" ) ) }

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Custom Rule override fun visitExpression(expression: KtExpression) { if (invalidExpression(expression)) report( CodeSmell( issue, Entity.from(expression), "A message" ) ) }

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A few examples of our custom rules ▫ Forbid throwing exceptions ▫ Forbid using check or require ▫ Forbid usage of !! ▫ Flag unsafe third party methods ▫ Flag TODO comments without a Jira ticket

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Going Further ▫ Make the rule configurable from detekt.yml

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Custom Rule class MyCustomRule( config: Config ) : Rule(config) { private val enableFoo: Boolean by config(defaultValue = true) //… }

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Custom Rule class MyCustomRule( config: Config ) : Rule(config) { private val enableFoo: Boolean by config(defaultValue = true) //… }

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Custom Rule class MyCustomRule( config: Config ) : Rule(config) { private val enableFoo: Boolean by config(defaultValue = true) //… }

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More info… ▫ https:/ /detekt.dev/ ▫ https:/ /github.com/detekt/detekt ▫ https:/ /thebakery.dev/30/

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2. Kotlin Symbol Processor

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What is KSP? ▫ Lightweight Compiler Plugin ▫ Similar to (K)APT but faster ▫ Source code is read-only ▫ Code generation

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How does KSP work ▫ Called at compile time ▫ Processor can query files and/or declarations ▫ Can generate new code (but not modify existing one)

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Custom Processor class MyCustomSymbolProcessor( val codeGenerator: CodeGenerator, val logger: KSPLogger ) : SymbolProcessor { override fun process(resolver: Resolver): List { return emptyList() } }

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Custom Processor class MyCustomSymbolProcessor( val codeGenerator: CodeGenerator, val logger: KSPLogger ) : SymbolProcessor { override fun process(resolver: Resolver): List { return emptyList() } }

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Custom Processor class MyCustomSymbolProcessor( val codeGenerator: CodeGenerator, val logger: KSPLogger ) : SymbolProcessor { override fun process(resolver: Resolver): List { return emptyList() } }

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Custom Processor override fun process(resolver: Resolver): List { val deferred = mutableListOf() resolver.getSymbolsWithAnnotation("com.example.MyAnnotation") .forEach { if (!generateSomething(it)) deferred.add(it) } return deferred }

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Custom Processor override fun process(resolver: Resolver): List { val deferred = mutableListOf() resolver.getSymbolsWithAnnotation("com.example.MyAnnotation") .forEach { if (!generateSomething(it)) deferred.add(it) } return deferred }

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Custom Processor override fun process(resolver: Resolver): List { val deferred = mutableListOf() resolver.getSymbolsWithAnnotation("com.example.MyAnnotation") .forEach { if (!generateSomething(it)) deferred.add(it) } return deferred }

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Custom Processor override fun process(resolver: Resolver): List { val deferred = mutableListOf() resolver.getSymbolsWithAnnotation("com.example.MyAnnotation") .forEach { if (!generateSomething(it)) deferred.add(it) } return deferred }

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Custom Processor override fun process(resolver: Resolver): List { val deferred = mutableListOf() resolver.getSymbolsWithAnnotation("com.example.MyAnnotation") .forEach { if (!generateSomething(it)) deferred.add(it) } return deferred }

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An example of custom processor ▫ Generate no-op implementation of annotated interfaces

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DataWriter.kt @NoOpImplementation internal interface DataWriter { fun write(element: T) fun write(data: List) }

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NoOpDataWriter.kt internal class NoOpDataWriter : DataWriter { public override fun write(element: T) { } public override fun write(data: List) { } }

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DataReader.kt @NoOpImplementation internal interface DataReader { fun readNext(): T? }

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NoOpDataReader.kt internal class NoOpDataReader : DataReader { public override fun readNext(): T? { return null } }

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Going Further ▫ KotlinPoet library

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KotlinPoet val file = FileSpec.builder("", "Greeter") .addType( TypeSpec.classBuilder("Greeter") .addFunction( FunSpec.builder("greet") .addParameter("name", String::class) .addStatement("println(%P)", "Hello, \$name").build() ).build() ).build()

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KotlinPoet val file = FileSpec.builder("", "Greeter") .addType( TypeSpec.classBuilder("Greeter") .addFunction( FunSpec.builder("greet") .addParameter("name", String::class) .addStatement("println(%P)", "Hello, \$name").build() ).build() ).build()

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KotlinPoet val file = FileSpec.builder("", "Greeter") .addType( TypeSpec.classBuilder("Greeter") .addFunction( FunSpec.builder("greet") .addParameter("name", String::class) .addStatement("println(%P)", "Hello, \$name").build() ).build() ).build()

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KotlinPoet val file = FileSpec.builder("", "Greeter") .addType( TypeSpec.classBuilder("Greeter") .addFunction( FunSpec.builder("greet") .addParameter("name", String::class) .addStatement("println(%P)", "Hello, \$name").build() ).build() ).build()

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KotlinPoet class Greeter() { fun greet(name: String) { println("""Hello, $name""") } }

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More info… ▫ https:/ /kotlinlang.org/docs/ksp-overview.html ▫ https:/ /github.com/google/ksp ▫ https:/ /square.github.io/kotlinpoet/

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3. Gradle Plugin

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What is Gradle? ▫ Custom tasks ▫ Compile time checks ▫ Helper classes

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How does Gradle work ▫ Project object created by Gradle ▫ Plugin adds extension/tasks to it

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Custom Task open class MyCustomTask : DefaultTask() { init { group = "MyCompany" description = "Description of the task" } @TaskAction fun applyTask() { } }

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Custom Task open class MyCustomTask : DefaultTask() { init { group = "MyCompany" description = "Description of the task" } @TaskAction fun applyTask() { } }

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Custom Task open class MyCustomTask : DefaultTask() { init { group = "MyCompany" description = "Description of the task" } @TaskAction fun applyTask() { } }

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Custom Extension open class MyCustomExtension( var outputFile: File = File(DEFAULT_OUTPUT_FILENAME), var enableSomething: Boolean = false )

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Custom Plugin class MyCustomPlugin : Plugin { override fun apply(target: Project) { val myExtension = target.extensions .create("myExtension", MyCustomExtension::class.java) val myTask = target.tasks .create("myTask", MyCustomTask::class.java) myTask.extension = myExtension } }

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Custom Plugin class MyCustomPlugin : Plugin { override fun apply(target: Project) { val myExtension = target.extensions .create("myExtension", MyCustomExtension::class.java) val myTask = target.tasks .create("myTask", MyCustomTask::class.java) myTask.extension = myExtension } }

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Custom Plugin class MyCustomPlugin : Plugin { override fun apply(target: Project) { val myExtension = target.extensions .create("myExtension", MyCustomExtension::class.java) val myTask = target.tasks .create("myTask", MyCustomTask::class.java) myTask.extension = myExtension } }

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Custom Plugin class MyCustomPlugin : Plugin { override fun apply(target: Project) { val myExtension = target.extensions .create("myExtension", MyCustomExtension::class.java) val myTask = target.tasks .create("myTask", MyCustomTask::class.java) myTask.extension = myExtension } }

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Custom Plugin class MyCustomPlugin : Plugin { override fun apply(target: Project) { val myExtension = target.extensions .create("myExtension", MyCustomExtension::class.java) val myTask = target.tasks .create("myTask", MyCustomTask::class.java) myTask.extension = myExtension } }

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An example of custom Gradle Tasks ▫ Compute dependencies size and OSS Licenses ▫ Keep track of API Surface ▫ Generate Data Class from JSON Schema ▫ From a remote git repository

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Going Further ▫ Link tasks together

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Custom Plugin override fun apply(target: Project) { // ... target.afterEvaluate { p -> p.tasks.withType(KotlinCompile::class.java) { dependsOn(myTask) } } }

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More info… ▫ https:/ /docs.gradle.org/current/userguide/custom_plugins.html ▫ https:/ /www.youtube.com/watch?v=ww0D8WMWPXc ▫ https:/ /speakerdeck.com/xgouchet/rock-the-gradle-mobileera

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4. Kotlin Compiler Plugin Let’s start with the first set of slides

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What is it? ▫ Plugin getting access to Kotlin source code / IR ▫ Can manipulate the code before compilation into JVM/JS/… ▫ Similar to Aspect Oriented Programming

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Cross-cutting concerns

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How does it work Parsing Resolution Analysis Code Generation Source Code PSI (AST) IR JVM JS Native

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Compiler Plugin ▫ Kotlin Compiler Plugin ▫ Gradle Plugin / Maven Plugin ▫ IDE Plugin (icons / syntax)

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Examples of Kotlin Compiler Plugins ▫ Generate Compose boilerplate code ▫ All-open makes all class open by default

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More info… ▫ https:/ /www.youtube.com/watch?v=w-GMlaziIyo ▫ https:/ /arrow-kt.io/docs/meta/ ▫ https:/ /medium.com/@heyitsmohit/writing-kotlin-compiler-pl ugin-with-arrow-meta-cf7b3689aa3e

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*. A little bit more Let’s start with the first set of slides

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PSI Viewer ▫ IDE Plugin for Intellij Idea and Android Studio ▫ Displays the actual PSI for the open tab

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*. Conclusion Let’s start with the first set of slides

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Detekt Gradle KSP KCP

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“ Your Detekt rules, KSP, Gradle scripts are still code. Keep them as clean, maintainable and trustworthy as your production code

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Useful links ▫ https:/ /github.com/datadog/dd-sdk-android

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Thank You! Any questions? @xgouchet @datadoghq Unsplash photo by @marcosjluiz

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Credits Special thanks to all the people who made and released these awesome resources for free: ▫ Presentation template by SlidesCarnival ▫ Photographs by Unsplash 79