Meta-Programming with Kotlin - Droidkaigi 2020

Kotlin has become go-to language for Android developers all over the world and the language itself has a large number of feature sets.
With greater acceptance of language, we look at how we can leverage power of Kotlin for meta-programming.
Through the talk, we'll introduce what Meta-Programming is and how we do it on day to day basis. We'll see how using Kotlin's internal compiler API, we can parse kotlin files, pull data out of it and go through various applications of this data such as custom documentation for API code and much more.
We'll also look at various approaches of source code generation for Kotlin files and how we can leverage them in projects.

Transcript

1. Meta-Programming with Kotlin @_jitinsharma Jitin Sharma
2. Open Ended
3. Open Ended Automation
4. Open Ended Automation Kotlin
5. Meta-Programming
6. Code Generators Code Parsers
7. Code Generators Code Parsers Annotation Processors?
8. Code Generators Code Parsers Annotation Processors? Retrofit Gson Dagger
9. Source Code Parsers
10. Source Code Parsers? • Gain insights over large codebase • Build static analysis tools • Documentation!
11. Anatomy of Source Code
12. File Class class… Functions Variables • abstract • interface • static • …. • private • protected • public • ….
13. File Classes Functions Variables class… Functions Variables • abstract • interface • object • companion • data • …. • private • internal • typealias • ….
14. val source: String = System.getProperty("user.dir") class Generator : GeneratorConfig { private var replaceIfNecessary = false override fun createConfig(config: Config) { } inner class Template { ... } data class Model(...) }
15. Program Structure Interface
16. PSI • Provides hierarchal content of code • Works across languages
17. PSI PsiFileFactory .getInstance(project) .createFileFromText(KotlinLanguage.INSTANCE, text)
18. PSI PsiFileFactory .getInstance(project) .createFileFromText(KotlinLanguage.INSTANCE, text) private val project by lazy { KotlinCoreEnvironment.createForProduction( Disposer.newDisposable(), CompilerConfiguration(), EnvironmentConfigFiles.JVM_CONFIG_FILES ).project }
19. implementation("org.jetbrains.kotlin:kotlin-compiler-embeddable:1.3.61")
20. PsiFile PsiElement PsiElement PsiElement …
21. PsiFile PsiElement PsiElement PsiElement … KtFile
22. ArrowView.kt import android.content.Context import android.graphics.Canvas import android.graphics.Color class ArrowView(context: Context, sides: Float, val base: Float) : View(context) { private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView }
23. ArrowView.kt import android.content.Context import android.graphics.Canvas import android.graphics.Color class ArrowView(context: Context, sides: Float, val base: Float) : View(context) { private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView }
24. ArrowView.kt KtFile }
25. ArrowView.kt import android.content.Context import android.graphics.Canvas import android.graphics.Color class ArrowView(context: Context, sides: Float, val base: Float) : View(context) { private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView }
26. import android.content.Context import android.graphics.Canvas import android.graphics.Color KtImportList KtImportDirective }
27. import android.content.Context import android.graphics.Canvas import android.graphics.Color KtImportList KtImportAlias as AndroidColor KtImportDirective }
28. ArrowView.kt import android.content.Context import android.graphics.Canvas import android.graphics.Color class ArrowView(context: Context, sides: Float, val base: Float) : View(context) { private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView }
29. class ArrowView(context: Context, sides: Float, val base: Float) : View(context) { KtClass KtSuperTypeEntries } } KtPrimaryConstructor }
30. ArrowView.kt import android.content.Context import android.graphics.Canvas import android.graphics.Color class ArrowView(context: Context, sides: Float, val base: Float) : View(context) { private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView }
31. private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView } KtParameter KtModifierKeywordToken KtTypeReference KtBlockExpression } } } } KtExpression
32. private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView } /** * Generates an imageview dynamically */ KDoc }
33. ArrowView.kt import android.content.Context import android.graphics.Canvas import android.graphics.Color class ArrowView(context: Context, sides: Float, val base: Float) : View(context) { private fun createIconView(drawable: Drawable): ImageView { val imageView = AppCompatImageView(context) imageView.scaleType = ImageView.ScaleType.CENTER ... return imageView }
34. PSI-Tree ktFile.acceptChildren(// PsiElementVisitor()) ktFile.acceptChildren(classRecursiveVisitor { ktClass -> }) ktFile.acceptChildren(namedFunctionRecursiveVisitor { ktFunction -> })
36. Plugin
37. Source Code as Data Source Code
38. Source Code as Data Source Code @Serializable data class ParsedFile( var name: String, var doc: String? = null, @SerialName("classes") var parsedClasses: List<ParsedClass>? = null, @SerialName("functions") var parsedFunctions: List<ParsedFunction>? = null, @SerialName("properties") var parsedVariables: List<ParsedVariable>? = null )
39. Source Code as Data Source Code @Serializable data class ParsedFile( var name: String, var doc: String? = null, @SerialName("classes") var parsedClasses: List<ParsedClass>? = null, @SerialName("functions") var parsedFunctions: List<ParsedFunction>? = null, @SerialName("properties") var parsedVariables: List<ParsedVariable>? = null )
40. Documentation • dokka != configurable • Build custom documentation
41. Static Analysis • Access to every piece of code in your codebase • ktlint!
42. Source Code Generators
43. Source Code Generators? • Avoid manual boilerplate code • Promote templating • Create more formalised code base
44. Writing Source Code • Easy string manipulation with regex and indent extensions • Java8 provides better file operations and Streams! • Coroutines for async
45. Writing Templates val text = """ class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) } } """.trimIndent() Files.write(path, text)
46. Writing Templates val text = """ class $activityName : BaseActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.$layoutName) } } """.trimIndent() Files.write(path, text)
47. Structured Codegen https://github.com/square/kotlinpoet
48. Structured Codegen FileSpec.builder("in.jitinsharma", "MainActivity.kt") TypeSpec.classBuilder() FunSpec.builder("onCreate") addParameter() addModifiers(KModifier.INTERNAL) superclass(TypeVariableName.invoke("AppCompatActivity"))
49. Schema based Codegen { "source": "...", “type": "...", "paths": [] } Source Code
50. Schema based Codegen { "sourceClass": "MainActivity.kt", "sourceXml": "activity_main", "adapter": "CountryListAdapter", "views": [ { "layoutFileName": "country_list_header.xml", "layoutType": "TextView", "viewHolderName": "CountryListHeaderViewHolder" } ] }
51. SqlDelight CREATE TABLE Photos ( id INTEGER NOT NULL, title TEXT NOT NULL ); insert: INSERT INTO Photos (id, title) VALUES (?, ?); getAll: SELECT * FROM Photos;
52. SqlDelight interface PhotoQueries : Transacter { fun <T : Any> getAll(mapper: ( id: String, title: String ) -> T): Query<T> fun getAll(): Query<Photos> fun insert( id: String, title: String ) }
53. val db = Database(AndroidSqliteDriver(Database.Schema, context, “photo.db”)) db.photoQueries.getAll() -> List<Photos> SqlDelight - MPP
55. <T : Closeable?, R> T.use()
56. <T : Closeable?, R> T.use() codeString .lineSequence() .map { line -> }
57. <T : Closeable?, R> T.use() codeString .lineSequence() .map { line -> } Files.find(path, 10, BiPredicate { path, _ -> })
58. <T : Closeable?, R> T.use() codeString .lineSequence() .map { line -> } Files.find(path, 10, BiPredicate { path, _ -> }) Files.write( path, classString.toByteArray(), StandardOpenOption.CREATE_NEW, StandardOpenOption.TRUNCATE_EXISTING)
59. . ├── app ├── module-1 ├── module-2 ├── … └── tools-module java -jar project/build/libs/tools.jar --param
60. . ├── app ├── module-1 ├── module-2 ├── … └── script.kts kscript
61. Fun fact
62. Thanks @_jitinsharma