Kotlin-friendly Annotation Processing (AppsConf 2018)

When promoting Kotlin over Java to your friend the first argument you’ll probably use will be its powerful syntax: in-house nullability support, default arguments, delegated properties, data & sealed classes, etc. These features are really the stuff we’re benefiting from everyday, but if we’ll take Java annotation processors then sadly the only information they can get about our code will be Java-related and no info about Kotlin-specific features.

In this talk we’ll find out how to use Kotlin metadata added by the compiler to get info about Kotlin language features in the code and utilise it during annotation processing.

Video: https://youtu.be/rJ9BRDuvJ1I

Transcript

1. Kotlin-friendly Annotation Processing Sergey Ryabov
2. JSR-269
3. • Annotation processing works inside javac JSR-269
4. • Annotation processing works inside javac • Separate Annotation Processors are pluggable JSR-269
5. • Annotation processing works inside javac • Separate Annotation Processors are pluggable • Gradle’s annotationProcessor dependencies configuration JSR-269
6. • Annotation processing works inside javac • Separate Annotation Processors are pluggable • Gradle’s annotationProcessor dependencies configuration • /META-INF/services/javax.annotation.processing.Processor 
 declares your AP’s main entry point JSR-269
7. • Annotation processing works inside javac • Separate Annotation Processors are pluggable • Gradle’s annotationProcessor dependencies configuration • /META-INF/services/javax.annotation.processing.Processor 
 declares your AP’s main entry point • Multiple rounds of processing JSR-269
8. *.java JSR-269
9. *.java apt JSR-269
10. *.java apt javac JSR-269
11. Kotlin-way
12. • APT can’t process Kotlin sources — build KAPT Kotlin-way
13. • APT can’t process Kotlin sources — build KAPT • Kotlin’s own JSR-269 implementation? Kotlin-way
14. • APT can’t process Kotlin sources — build KAPT • Kotlin’s own JSR-269 implementation? • Generate Java code/stubs from Kotlin? Kotlin-way
15. • APT can’t process Kotlin sources — build KAPT • Kotlin’s own JSR-269 implementation? • Generate Java code/stubs from Kotlin? • Precompile Kotlin classes and feed them to javac? Kotlin-way
16. • APT can’t process Kotlin sources — build KAPT • Kotlin’s own JSR-269 implementation? • Generate Java code/stubs from Kotlin? • Precompile Kotlin classes and feed them to javac? Kotlin-way
17. • APT can’t process Kotlin sources — build KAPT • Kotlin’s own JSR-269 implementation? • Generate Java code/stubs from Kotlin? • Precompile Kotlin classes and feed them to javac? Kotlin-way
18. • APT can’t process Kotlin sources — build KAPT • Kotlin’s own JSR-269 implementation? • Generate Java code/stubs from Kotlin? • Precompile Kotlin classes and feed them to javac? Kotlin-way
19. • APT can’t process Kotlin sources — build KAPT • Kotlin’s own JSR-269 implementation? • Generate Java code/stubs from Kotlin? • Precompile Kotlin classes and feed them to javac? • No multiple APT rounds over generated Kotlin files Kotlin-way
20. *.kt Kotlin-way
21. *.kt kapt Kotlin-way
22. *.kt kapt *.java Kotlin-way
23. *.kt kapt apt *.java Kotlin-way
24. *.kt kapt kotlinc apt *.java Kotlin-way
25. class KotlinProcessor : AbstractProcessor() { } JSR-269
26. class KotlinProcessor : AbstractProcessor() { override fun getSupportedOptions(): Set<String> } JSR-269
27. class KotlinProcessor : AbstractProcessor() { override fun getSupportedOptions(): Set<String> override fun getSupportedAnnotationTypes(): Set<String> } JSR-269
28. class KotlinProcessor : AbstractProcessor() { override fun getSupportedOptions(): Set<String> override fun getSupportedAnnotationTypes(): Set<String> override fun getSupportedSourceVersion(): SourceVersion } JSR-269
29. class KotlinProcessor : AbstractProcessor() { override fun getSupportedOptions(): Set<String> override fun getSupportedAnnotationTypes(): Set<String> override fun getSupportedSourceVersion(): SourceVersion override fun init(processingEnv: ProcessingEnvironment) } JSR-269
30. class KotlinProcessor : AbstractProcessor() { override fun getSupportedOptions(): Set<String> override fun getSupportedAnnotationTypes(): Set<String> override fun getSupportedSourceVersion(): SourceVersion override fun init(processingEnv: ProcessingEnvironment) override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean } JSR-269
31. class KotlinProcessor : AbstractProcessor() { override fun getSupportedOptions(): Set<String> override fun getSupportedAnnotationTypes(): Set<String> override fun getSupportedSourceVersion(): SourceVersion override fun init(processingEnv: ProcessingEnvironment) override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean } JSR-269
32. Problems
33. Problems • No info about Kotlin-specifics is available for Annotation Processors
34. Problems • No info about Kotlin-specifics is available for Annotation Processors • No Nullability
35. Problems • No info about Kotlin-specifics is available for Annotation Processors • No Nullability • No default arguments
36. Problems • No info about Kotlin-specifics is available for Annotation Processors • No Nullability • No default arguments • No sealed & data classes
37. Problems • No info about Kotlin-specifics is available for Annotation Processors • No Nullability • No default arguments • No sealed & data classes • …
38. Problems • No info about Kotlin-specifics is available for Annotation Processors • No Nullability • No default arguments • No sealed & data classes • … • No nothing!
40. Dad! APT can’t get any Kotlin info. And StackOverflow can’t help!
41. Dad! APT can’t get any Kotlin info. And StackOverflow can’t help! If even StackOverflow keeps silence…
42. Dad! APT can’t get any Kotlin info. And StackOverflow can’t help! If even StackOverflow keeps silence… B-b-b-but compiler..?
43. Dad! APT can’t get any Kotlin info. And StackOverflow can’t help! If even StackOverflow keeps silence… B-b-b-but compiler..? Well, this city has a Hero!
44. @Metadata
45. @Metadata( mv = {1, 1, 11}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0080\u0001\n\u0002\u0018\u0002\n\u0002\u0018\u0002\n\u00… d2 = {""Lxyz/ryabov/gsonkot/User;", "", "id", "", "username", "", "isAdmin ) public final class User { ... }
46. @Metadata
47. @Metadata • Provides Kotlin-specific info
48. @Metadata • Provides Kotlin-specific info • Class-level annotation
49. @Metadata • Provides Kotlin-specific info • Class-level annotation • Accessible both at compile time and runtime
50. @Metadata • Provides Kotlin-specific info • Class-level annotation • Accessible both at compile time and runtime • Used by compiler as well
51. @Metadata • mv • bv • k • d1 • d2 • xs • xi • pn
52. @Metadata • metadataVersion • bytecodeVersion • kind • data1 • data2 • extraString • extraInt • packageName
53. What can we do with that?
54. What can we do with that? Parse data1 Protocol Buffers using kind to define its format
55. What can we do with that? Parse data1 Protocol Buffers using kind to define its format https://github.com/JetBrains/kotlin/blob/master/core/metadata/src/metadata.proto
56. Protocol Buffers
57. Protocol Buffers
58. What tools do we have?
59. What tools do we have? • Hands
60. What tools do we have? • Hands
61. What tools do we have? • Hands • Use kotlin-metadata by Eugenio Marletti
 https://github.com/Takhion/kotlin-metadata
62. What tools do we have? • Hands • Use kotlin-metadata by Eugenio Marletti
 https://github.com/Takhion/kotlin-metadata • Or…

63. What tools do we have? • Hands • Use kotlin-metadata by Eugenio Marletti
 https://github.com/Takhion/kotlin-metadata • Or… kotlinx-metadata by JetBrains
 https://github.com/JetBrains/kotlin/tree/master/libraries/kotlinx-metadata/jvm
64. Two patterns
65. Two patterns • Visitors API
66. Two patterns • Visitors API • DOM-like API
67. Visitors API
68. Visitors API public interface Element { <R, P> R accept(ElementVisitor<R, P> v, P p); }
69. Visitors API public interface ElementVisitor<R, P> { R visit(Element e, P p); }
70. Visitors API public interface ElementVisitor<R, P> { R visit(Element e, P p); R visitPackage(PackageElement e, P p); }
71. Visitors API public interface ElementVisitor<R, P> { R visit(Element e, P p); R visitPackage(PackageElement e, P p); R visitType(TypeElement e, P p); }
72. Visitors API public interface ElementVisitor<R, P> { R visit(Element e, P p); R visitPackage(PackageElement e, P p); R visitType(TypeElement e, P p); R visitVariable(VariableElement e, P p); }
73. Visitors API public interface ElementVisitor<R, P> { R visit(Element e, P p); R visitPackage(PackageElement e, P p); R visitType(TypeElement e, P p); R visitVariable(VariableElement e, P p); R visitExecutable(ExecutableElement e, P p); }
74. Visitors API public interface ElementVisitor<R, P> { R visit(Element e, P p); R visitPackage(PackageElement e, P p); R visitType(TypeElement e, P p); R visitVariable(VariableElement e, P p); R visitExecutable(ExecutableElement e, P p); R visitTypeParameter(TypeParameterElement e, P p); }
75. Visitors API public interface ElementVisitor<R, P> { R visit(Element e, P p); R visitPackage(PackageElement e, P p); R visitType(TypeElement e, P p); R visitVariable(VariableElement e, P p); R visitExecutable(ExecutableElement e, P p); R visitTypeParameter(TypeParameterElement e, P p); R visitUnknown(Element e, P p); }
76. Visitors API
77. Visitors API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { return false } }
78. Visitors API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(Builder::class.java)) { }. return false } }
79. Visitors API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(Builder::class.java)) { element.accept(visitor, null) }.. return false } }
80. Visitors API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(Builder::class.java)) { val visitor = object : ElementScanner7<Unit, Unit>() { override fun visitVariable(e: VariableElement, p: Unit?) { handleVariable(e) } } element.accept(visitor, null) }. return false } }
81. Visitors API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(Builder::class.java)) { val visitor = object : ElementScanner7<Unit, Unit>() { override fun visitVariable(e: VariableElement, p: Unit?) { handleVariable(e) } } element.accept(visitor, null) }. return false } }
82. Two patterns • Visitors API • DOM-like API
83. DOM-like API
84. DOM-like API public interface Element { }
85. DOM-like API public interface Element { Element getEnclosingElement(); }
86. DOM-like API public interface Element { Element getEnclosingElement(); List<? extends Element> getEnclosedElements(); }
87. DOM-like API public interface Element { Element getEnclosingElement(); List<? extends Element> getEnclosedElements(); ElementKind getKind(); }
88. DOM-like API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(BindView::class.java)) { } return false } }
89. DOM-like API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(BindView::class.java)) { } return false } }
90. DOM-like API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(BindView::class.java)) { if (element.kind == ElementKind.FIELD) { handleVariable(element as VariableElement) }. } return false } }
91. DOM-like API class KotlinProcessor : AbstractProcessor() { override fun process( annotations: Set<TypeElement>, roundEnv: RoundEnvironment ): Boolean { for (element in roundEnv.getElementsAnnotatedWith(BindView::class.java)) { if (element.kind == ElementKind.FIELD) { handleVariable(element as VariableElement) }. } return false } }
92. kotlinx-metadata
93. kotlinx-metadata Has only low-level Visitors API
94. Visitors API
95. Visitors API abstract class KmFunctionVisitor abstract class KmPropertyVisitor abstract class KmPackageVisitor abstract class KmClassVisitor abstract class KmConstructorVisitor abstract class KmValueParameterVisitor abstract class KmLambdaVisitor abstract class KmTypeVisitor abstract class KmTypeAliasVisitor abstract class KmTypeParameterVisitor
96. Visitors API abstract class KmClassVisitor { open fun visit*(...) }.
97. Visitors API abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
98. Visitors API class Type<out E : UpperBoundType> abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
99. Visitors API class Type<out E : UpperBoundType> abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
100. Visitors API class Type<out E : UpperBoundType> abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
101. Visitors API class Type<out E : UpperBoundType> abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
102. Visitors API class Type<out E : UpperBoundType> abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
103. Visitors API class Type<out E : UpperBoundType> abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
104. Visitors API class Type<out E : UpperBoundType> abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
105. Visitors API abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }.
106. Visitors API abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }. interface ElementVisitor<R, P> { R visitTypeParameter( TypeParameterElement e, P p ); }
107. Visitors API abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }. interface ElementVisitor<R, P> { R visitTypeParameter( TypeParameterElement e, P p ); }
108. Visitors API abstract class KmClassVisitor { open fun visitTypeParameter( flags: Flags, name: String, id: Int, variance: KmVariance ): KmTypeParameterVisitor? }. interface ElementVisitor<R, P> { R visitTypeParameter( TypeParameterElement e, P p ); }
109. GsonTypeAdapter
110. GsonTypeAdapter @GsonAdapter data class User( val id: Long, val username: String, val isAdmin: Boolean )
111. val annotation = GsonAdapter::class.java for (element in roundEnv.getElementsAnnotatedWith(annotation)) { val input = getInputFrom(element) ?: continue if (!input.generateAndWrite()) return true }
112. val annotation = GsonAdapter::class.java for (element in roundEnv.getElementsAnnotatedWith(annotation)) { val input = getInputFrom(element) ?: continue if (!input.generateAndWrite()) return true }
113. val metadata = getMetadata(element)
114. fun getMetadata(element: Element): KotlinClassMetadata? { val annotation = element.getAnnotation(Metadata::class.java) val header = annotation.run { KotlinClassHeader(k, mv, bv, d1, d2, xs, pn, xi) }. return KotlinClassMetadata.read(header) }.
115. fun getMetadata(element: Element): KotlinClassMetadata? { val annotation = element.getAnnotation(Metadata::class.java) val header = annotation.run { KotlinClassHeader(k, mv, bv, d1, d2, xs, pn, xi) }. return KotlinClassMetadata.read(header) }.
116. fun getMetadata(element: Element): KotlinClassMetadata? { val annotation = element.getAnnotation(Metadata::class.java) val header = annotation.run { KotlinClassHeader(k, mv, bv, d1, d2, xs, pn, xi) }. return KotlinClassMetadata.read(header) }.
117. fun getMetadata(element: Element): KotlinClassMetadata? { val annotation = element.getAnnotation(Metadata::class.java) val header = annotation.run { KotlinClassHeader(k, mv, bv, d1, d2, xs, pn, xi) }. return KotlinClassMetadata.read(header) }.
118. sealed class KotlinClassMetadata { class Class : KotlinClassMetadata class FileFacade : KotlinClassMetadata class SyntheticClass : KotlinClassMetadata class MultiFileClassFacade : KotlinClassMetadata class MultiFileClassPart : KotlinClassMetadata class Unknown : KotlinClassMetadata }
119. sealed class KotlinClassMetadata { class Class : KotlinClassMetadata class FileFacade : KotlinClassMetadata class SyntheticClass : KotlinClassMetadata class MultiFileClassFacade : KotlinClassMetadata class MultiFileClassPart : KotlinClassMetadata class Unknown : KotlinClassMetadata }
120. val metadata = getMetadata(element)
121. val metadata = getMetadata(element) if (metadata !is KotlinClassMetadata.Class) { errorMustBeKotlinClass(element) return null }.
122. val metadata = getMetadata(element) if (metadata !is KotlinClassMetadata.Class) { errorMustBeKotlinClass(element) return null }. metadata.accept(object : KmClassVisitor() { })
123. val metadata = getMetadata(element) if (metadata !is KotlinClassMetadata.Class) { errorMustBeKotlinClass(element) return null }. metadata.accept(object : KmClassVisitor() { override fun visit(flags: Flags, name: ClassName) { } })
124. val metadata = getMetadata(element) if (metadata !is KotlinClassMetadata.Class) { errorMustBeKotlinClass(element) return null }. metadata.accept(object : KmClassVisitor() { override fun visit(flags: Flags, name: ClassName) { pkg = name.substringBeforeLast('/').fqName() className = name.substringAfterLast('/') fqClassName = name.fqName() } })
125. return null }. metadata.accept(object : KmClassVisitor() { override fun visit(flags: Flags, name: ClassName) { pkg = name.substringBeforeLast('/').fqName() className = name.substringAfterLast('/') fqClassName = name.fqName() } override fun visitConstructor(flags: Flags): KmConstructorVisitor? { } })
126. return null }. metadata.accept(object : KmClassVisitor() { override fun visit(flags: Flags, name: ClassName) { pkg = name.substringBeforeLast('/').fqName() className = name.substringAfterLast('/') fqClassName = name.fqName() } override fun visitConstructor(flags: Flags): KmConstructorVisitor? { if (!flags.isPrimaryConstructor) return null } })
127. val Flags.isPrimaryConstructor: Boolean get() = Flag.Constructor.IS_PRIMARY(this)
128. val Flags.isNullableType: Boolean get() = Flag.Type.IS_NULLABLE(this) val Flags.isDataClass: Boolean get() = Flag.Class.IS_DATA(this) val Flags.isPrimaryConstructor: Boolean get() = Flag.Constructor.IS_PRIMARY(this) val Flags.hasDefaultValue: Boolean get() = Flag.ValueParameter.DECLARES_DEFAULT_VALUE(this)
129. return null }. metadata.accept(object : KmClassVisitor() { override fun visit(flags: Flags, name: ClassName) { pkg = name.substringBeforeLast('/').fqName() className = name.substringAfterLast('/') fqClassName = name.fqName() } override fun visitConstructor(flags: Flags): KmConstructorVisitor? { if (!flags.isPrimaryConstructor) return null } })
130. pkg = name.substringBeforeLast('/').fqName() className = name.substringAfterLast('/') fqClassName = name.fqName() } override fun visitConstructor(flags: Flags): KmConstructorVisitor? { if (!flags.isPrimaryConstructor) return null return object : KmConstructorVisitor() { override fun visitValueParameter( flags: Flags, name: String ): KmValueParameterVisitor? { }. }. } })
131. } override fun visitConstructor(flags: Flags): KmConstructorVisitor? { if (!flags.isPrimaryConstructor) return null return object : KmConstructorVisitor() { override fun visitValueParameter( flags: Flags, name: String ): KmValueParameterVisitor? { return object : KmValueParameterVisitor() { override fun visitType(flags: Flags): KmTypeVisitor? { return ... } } }. }. } })
132. return object :.KmTypeVisitor().{. }.
133. return object :.KmTypeVisitor().{. override fun visitAbbreviatedType(flags: Flags): KmTypeVisitor? { } override fun visitArgument( flags: Flags, variance: KmVariance ): KmTypeVisitor? { } }.
134. class KmTypeInfoVisitor() :.KmTypeVisitor().{. }.
135. class KmTypeInfoVisitor( private val flags: Flags, private val onVisitEnd: (KmTypeInfoVisitor) -> Unit ) : KmTypeVisitor() {. }.
136. class KmTypeInfoVisitor( private val flags: Flags, private val onVisitEnd: (KmTypeInfoVisitor) -> Unit ) : KmTypeVisitor() {. lateinit var fqName: String var isNullable: Boolean = false private val typeArgs = arrayListOf<String>() }.
137. class KmTypeInfoVisitor( private val flags: Flags, private val onVisitEnd: (KmTypeInfoVisitor) -> Unit ) : KmTypeVisitor() { lateinit var fqName: String var isNullable: Boolean = false private val typeArgs = arrayListOf<String>() override fun visitEnd() { } }.
138. private val onVisitEnd: (KmTypeInfoVisitor) -> Unit ) : KmTypeVisitor() { lateinit var fqName: String var isNullable: Boolean = false private val typeArgs = arrayListOf<String>() override fun visitEnd() { if (typeArgs.isNotEmpty()) { fqName += typeArgs.joinToString(prefix = "<", postfix = ">") typeArgs.clear() }, isNullable = flags.isNullableType onVisitEnd(this) } }.
139. fqName += typeArgs.joinToString(prefix = "<", postfix = ">") typeArgs.clear() }, isNullable = flags.isNullableType onVisitEnd(this) } override fun visitClass(name: ClassName) { fqName = name.fqName() }. }.
140. onVisitEnd(this) } override fun visitClass(name: ClassName) { fqName = name.fqName() }. override fun visitAbbreviatedType(flags: Flags): KmTypeVisitor? { return KmTypeInfoVisitor(flags, typeResolver) { fqName = it.fqName typeArgs.clear() }. }, }.
141. onVisitEnd(this) } override fun visitClass(name: ClassName) { fqName = name.fqName() }. override fun visitAbbreviatedType(flags: Flags): KmTypeVisitor? { return KmTypeInfoVisitor(flags, typeResolver) { fqName = it.fqName typeArgs.clear() }. }, }.
142. fqName = name.fqName() }. override fun visitAbbreviatedType(flags: Flags): KmTypeVisitor? { return KmTypeInfoVisitor(flags, typeResolver) { fqName = it.fqName typeArgs.clear() }. },’ override fun visitTypeAlias(name: ClassName) { fqName = name.fqName() }. }.
143. return KmTypeInfoVisitor(flags, typeResolver) { fqName = it.fqName typeArgs.clear() }. }, override fun visitTypeAlias(name: ClassName) { fqName = name.fqName() }. override fun visitTypeParameter(id: Int) { fqName = typeResolver(id) ?: throw error("Missing param: id=$id") }, }.
144. override fun visitTypeAlias(name: ClassName) { fqName = name.fqName() }. override fun visitTypeParameter(id: Int) { fqName = typeResolver(id) ?: throw error("Missing param: id=$id") }, override fun visitArgument( flags: Flags, variance: KmVariance ): KmTypeVisitor? { return KmTypeInfoVisitor(flags, typeResolver) { typeArgs += it.fqName }, }, }.
145. override fun visitTypeAlias(name: ClassName) { fqName = name.fqName() }. override fun visitTypeParameter(id: Int) { fqName = typeResolver(id) ?: throw error("Missing param: id=$id") }, override fun visitArgument( flags: Flags, variance: KmVariance ): KmTypeVisitor? { return KmTypeInfoVisitor(flags, typeResolver) { typeArgs += it.fqName },. }, }.
146. } override fun visitConstructor(flags: Flags): KmConstructorVisitor? { if (!flags.isPrimaryConstructor) return null return object : KmConstructorVisitor() { override fun visitValueParameter( flags: Flags, name: String ): KmValueParameterVisitor? { return object : KmValueParameterVisitor() { override fun visitType(flags: Flags): KmTypeVisitor? { return ... }. }. }. }. } })
147. } override fun visitConstructor(flags: Flags): KmConstructorVisitor? { if (!flags.isPrimaryConstructor) return null return object : KmConstructorVisitor() { override fun visitValueParameter( flags: Flags, name: String ): KmValueParameterVisitor? { return object : KmValueParameterVisitor() { override fun visitType(flags: Flags): KmTypeVisitor? { return KmTypeInfoVisitor(flags, typeArgsRegistry::get) { parameters += Parameter(name, it.fqName, it.isNullable) } }. }. }. }. } })
148. SHOW ME THE CODE
149. Worth noting
150. Worth noting • Metadata has only partial info
151. Worth noting • Metadata has only partial info • Separate code model from generation
152. Worth noting • Metadata has only partial info • Separate code model from generation • Both Kotlin & Java can be supported in one place
153. Worth noting • Metadata has only partial info • Separate code model from generation • Both Kotlin & Java can be supported in one place • Multiplatform support will follow
154. Other applications?
155. Other applications? • Annotation processing with codegen
156. Other applications? • Annotation processing with codegen • Bytecode weaving
157. Other applications? • Annotation processing with codegen • Bytecode weaving • Code validation
158. Other applications? • Annotation processing with codegen • Bytecode weaving • Code validation • Generating headers for interop with other languages: TypeScript, C/C++
159. Links • Metadata ProtoBuffer spec: github.com/JetBrains/kotlin/blob/master/core/metadata/src/metadata.proto • kotlin-metadata by Eugenio Marletti: github.com/Takhion/kotlin-metadata • kotlinx-metadata by JetBrains: github.com/JetBrains/kotlin/tree/master/libraries/kotlinx-metadata/jvm • Value-based API for kotlinx-metadata: youtrack.jetbrains.com/issue/KT-26602 • Gson TypeAdapters codegen: github.com/colriot/GsonKotgen • KotlinPoet: github.com/square/kotlinpoet • Annotation Processing in a Kotlin World by Zac Sweers: youtu.be/_yaaCtWF8aE?t=18968 • Annotation Processing Boilerplate Destruction by Jake Wharton: youtu.be/dOcs-NKK-RA • Multiple KAPT rounds demo: github.com/Takhion/generate-kotlin-multiple-rounds
160. Kotlin-friendly Annotation Processing Sergey Ryabov @colriot