Intellij IDEA Plugins Crash Course Yuriy Artamonov 

Plan 1. IntelliJ IDEA Plugin System 2. Java Frameworks from IDE point of view 3. Let’s build a plugin 4. When not to build plugins at all? 5. What’s next? 2 

Motivation ■ Everyone has: in-house frameworks, libraries, configs, processes, etc ■ We cannot completely get rid of routine work related to source code, testing, deployment and maintenance We must fight! 3 

How to Fight Routine Work Options: ■ Build frameworks! ■ Generate code! ■ Improve your tools - IDE 4 

Let’s share IntelliJ IDEA Knowledge 5 

Plugins Can Provide Tons of Features ★ Languages and file formats ★ Static code analysis ★ Code navigation ★ Editor improvements ★ Refactoring and code generation ★ Communication with thirdparty tools and services ★ Code migration from old APIs ... 6 

Key Mechanisms of IntelliJ IDEA ■ Components and services ■ Virtual File System (VFS) ■ Languages parsing and representation (PSI) ■ Code editor ■ Inspections ■ File indexes ■ Background processes ■ UI library ■ Extension points IntelliJ Platform IDEA CE (Java, Groovy, Kotlin) PHP Support Ruby Support IDEA Ultimate PHP Storm RubyMine 7 

Plugin System All JetBrains IDEs consist of plugins: 1. Plugin classes loaded with a separate class loader 2. Each plugin implements extension points of IDE and may provide its own 3. Plugins may depend on IDE modules and other plugins 8 Groovy Plugin Java Plugin Properties Plugin Ultimate Modules optional 

How to start 9 1. Check/Enable Plugin DevKit 2. Create Gradle project with IntelliJ Platform Plugin option 3. Declare and implement extension points We strongly recommend using Kotlin! 

Plugin Structure .../resources/META-INF/plugin.xml micronaut-intellij-plugin Micronaut Framework Support com.intellij.modules.java

Extension Points ■ Thousands of them: action, inspection, intention action, reference contributor, ui settings group, language parser, language formatter и т.д. ■ Registered in XML-file – plugin.xml manifest ■ You can find them: LangExtensionPoints.xml, PlatformExtensionPoints.xml, VcsExtensionPoints.xml, etc. Example: Groovy – plugin ( plugin.xml > 1300 LOC ) github.com/JetBrains/intellij-community 11 

Micronaut Modern JVM Framework for lightweight modular applications (Java / Kotlin / Groovy) Features: ■ Dependency Injection ■ HTTP Web Services (Sync/Async) ■ HTTP Client ■ Data Repositories ■ Compile-time everywhere ■ AOT Compatible 12 

References 1. Graeme Rocher - Introduction to Micronaut 2. Kirill Tolkachev, Maxim Gorelikov (RU) - Micronaut vs Spring Boot, или Кто тут самый маленький? 13 

What do we need to support in the plugin? 14 

First Try Problem: 1. Create a project 2. Run 3. Profit Nothing happens! Documentation: If you are using Java or Kotlin and IntelliJ IDEA make sure you have enabled annotation processing. 15 Let’s check that Annotations Processors are enabled in Micronaut projects! 

Find Proper Extenstion Point 1. Register class of com.intellij.openapi.startup.StartupActivity: 2. Use UI Inspector to find the IDE mechanisms (Ctrl+Alt+Click): 16 

Implicit Usages Problem: frameworks are smart and love implicit logic. @Controller class WelcomeController { @View("welcome") @Get("/") public HttpResponse welcome() { return HttpResponse.ok(); } } 💡 Class ‘WelcomeController’ is never used. 17 Let’s teach IDE how to understand implicits! 

Implicit Usage Provider New extension point: class MicronautImplicitUsageProvider : ImplicitUsageProvider { override fun isImplicitWrite(element: PsiElement?): Boolean { TODO() } override fun isImplicitRead(element: PsiElement?): Boolean { TODO() } override fun isImplicitUsage(element: PsiElement?): Boolean { TODO() } } 18 

Languages Syntax Basics PSI - Program Structure Interface, a special representation: ■ Structure of the project and code ■ Includes semantic data ■ Everything is PsiElement (almost) ■ Every language provides its own PSI elements 19 PsiFile PsiElement PsiElement PsiElement PsiElement PSI Tree 

Java PSI model Key elements: ■ PsiJavaFile ■ PsiImportList ■ PsiClass ■ PsiAnnotation ■ PsiField ■ PsiMethod ■ ... See: Tools - View PSI Structure of Current File 20 

How to find a problem in cron expressions Example: @Singleton public class VisitProcessor { @Scheduled(cron = "0 55 11 * * * .") public void run() { // do work } } What’s wrong here? 21 

Create Inspections Inspection engine: ■ Static analysis on the fly ■ Traverses PSI tree ■ Can provide quick fixes See: LocalInspectionTool LocalQuickFix 22 

Check @Scheduled cron expression New inspection in plugin.xml: Inspection class: class MicronautScheduledInspection : AbstractBaseJavaLocalInspectionTool() { override fun checkMethod(method: PsiMethod, manager: InspectionManager, isOnTheFly: Boolean) : Array? { // check here return ProblemDescriptor.EMPTY_ARRAY } } 23 

JVM Languages Zoo Unified Abstract Syntax Tree (UAST) ■ Describes JVM languages superset: Java, Kotlin и Groovy ■ Elements ○ UElement, UFile, UClass, UMember, UField, UMethod, ... ■ Blocks ○ UComment, UDeclaration, UExpression, UBlockExpression, UCallExpression, USwitchExpression, … ■ Use PSI if needed (resolve) ■ Code generation is limited (use PSI) See: org.jetbrains.uast 24 ПРАВИЛЬНЫЙ ЗООПАРК 

UAST inspections 1. Change language to UAST in plugin.xml 2. Obtain UElement 3. Find a problem in UAST tree (or in synthetic PSI) 4. Go back to sourcePsi 5. Register problem for sourcePsi See: Tools - Internal Actions - Dump UAST Tree Examples: intellij-community/plugins/devkit/ и Android Studio 25 

Code navigation Publish/Subcribe with @EventListener: ■ Events are hard to understand ■ Developers hate them ■ IDE does not help Idea: Icons on gutter with navigation to publishers / subsribers! See: LineMarkerProvider RelatedItemLineMarkerProvider 26 

Base Indexes ■ Word Index ○ Key – word hashcode ○ Value – bitmask of source (in code, in comment, in string literal) ○ Used in Find in Path, Find Usages ■ File names and file types indexes ■ Java Class Names index See: PsiSearchHelper 27 

How to find something useful Module java-indexing-api provides search methods for standard indexes: ■ ReferencesSearch ■ MethodReferenceSearch ■ AnnotatedElementsSearch ■ … Query MethodReferencesSearch.search(psiMethod, scope, strict) Query AnnotatedElementsSearch.searchPsiMethods(annotationClass, scope) 28 

Cache it! Search is slow, cache it if possible 29 val cacheManager = CachedValuesManager.getManager(module.project) return cacheManager.getCachedValue(module) { val result = heavyFunction(module) CachedValueProvider.Result.create( result , PsiModificationTracker.MODIFICATION_COUNT, // << track code changes everywhere ProjectRootManager.getInstance(module.project) // and in project structure ) } See: CachedValuesManager 

References in PSI tree ■ References sets relation between: usage ➜ declaration ■ May provide auto completion ■ We can add references without changing the underlying language See: PsiReferenceContributor PsiLanguageInjectionHost 30 

Provide References In Micronaut any annotation may contain references to application.properties keys in a form of ${some.property-name}: @Value("${datasources.default.url}") private String datasourceUrl; Idea: let’s connect those strings and config keys with PSI reference 31 

What’s next? 32 

What do We Usually Support in Framework Plugins Main extension points: ■ Implicit Usages ■ References ■ Inspections and Quick Fixes ■ Intention Actions ■ Line Markers ■ Language Injection ■ New Project Wizard ■ File Templates 33 

Sometimes it Requires Tons of Code Spring Framework Support in numbers: ■ 260k LOC Java ■ 20k LOC Kotlin ■ 350k LOC Total ■ 3400 Tests 34 

Deploy Plugin for Your Company Requirements: ■ HTTP server (e.g. Nginx) ■ Plugins registry file: updatePlugins.xml

How to Live without Plugins If there is a chance to not write a plugin - do not create a plugin! Instead: ■ Suppress unused for class annotated with … ■ Setup required plugins and inspections ■ Commit 📁 .idea directory to VCS ■ Setup Language Injection ■ Use JetBrains annotations (nullity, contract, pure, language) dependencies { compileOnly 'org.jetbrains:annotations:17.0.0' } 36 

Structural Search for Inspections Check code without plugin: ■ Enable Inspections - Structured Search Inspection ■ Setup search templates Example: @Inject $Field$ 37 

Links ■ IntelliJ IDEA CE Sources: github.com/JetBrains/intellij-community ■ Plugin DevKit Docs: jetbrains.org/intellij/sdk/docs/basics.html ■ Forum: IntelliJ IDEA Open API and Plugin Development 38 

Questions ? Source code: github.com/jreznot/micronaut-intellij-plugin Twitter: @Yuriy_Artamonov