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Kotlin annotation processor example
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plugins { | |
id 'org.jetbrains.kotlin.jvm' version '1.3.61' | |
} | |
version 'unspecified' | |
repositories { | |
mavenCentral() | |
} | |
dependencies { | |
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8" | |
} | |
compileKotlin { | |
kotlinOptions.jvmTarget = "1.8" | |
} | |
compileTestKotlin { | |
kotlinOptions.jvmTarget = "1.8" | |
} |
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plugins { | |
id 'org.jetbrains.kotlin.jvm' version '1.3.61' | |
id 'org.jetbrains.kotlin.kapt' version '1.3.61' | |
} | |
version 'unspecified' | |
repositories { | |
mavenCentral() | |
} | |
dependencies { | |
implementation project(':annotation') | |
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8" | |
implementation 'com.squareup:kotlinpoet:1.5.0' | |
implementation "com.google.auto.service:auto-service:1.0-rc6" | |
kapt "com.google.auto.service:auto-service:1.0-rc6" | |
} | |
compileKotlin { | |
kotlinOptions.jvmTarget = "1.8" | |
} | |
compileTestKotlin { | |
kotlinOptions.jvmTarget = "1.8" | |
} |
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package com.example.annotation.annotation | |
@Retention(AnnotationRetention.SOURCE) | |
@Target(AnnotationTarget.FUNCTION) | |
@MustBeDocumented | |
annotation class FeatureFlag(val key: String, val defaultValue: Boolean) |
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package com.example.annotation.codegen | |
import com.example.annotation.annotation.FeatureFlag | |
import com.example.annotation.annotation.FeatureFlagGroup | |
import com.google.auto.service.AutoService | |
import com.squareup.kotlinpoet.* | |
import com.squareup.kotlinpoet.ParameterizedTypeName.Companion.parameterizedBy | |
import java.io.File | |
import javax.annotation.Generated | |
import javax.annotation.processing.AbstractProcessor | |
import javax.annotation.processing.Processor | |
import javax.annotation.processing.RoundEnvironment | |
import javax.annotation.processing.SupportedOptions | |
import javax.lang.model.SourceVersion | |
import javax.lang.model.element.* | |
import javax.tools.Diagnostic | |
private const val KAPT_KOTLIN_GENERATED_OPTION_NAME = "kapt.kotlin.generated" | |
@AutoService(Processor::class) | |
@SupportedOptions(KAPT_KOTLIN_GENERATED_OPTION_NAME) | |
class FeatureFlagCodegen : AbstractProcessor() { | |
override fun getSupportedAnnotationTypes(): Set<String> = setOf( | |
FeatureFlagGroup::class.java.name, | |
FeatureFlag::class.java.name | |
) | |
override fun getSupportedSourceVersion(): SourceVersion = SourceVersion.latestSupported() | |
override fun process(annotations: MutableSet<out TypeElement>, roundEnv: RoundEnvironment): Boolean { | |
if (roundEnv.processingOver()) return false | |
roundEnv.getElementsAnnotatedWith(FeatureFlagGroup::class.java) | |
.filter { it.kind == ElementKind.INTERFACE } | |
.forEach { featureFlagGroupElement -> | |
val featureFlagElements = featureFlagGroupElement.enclosedElements | |
.filter { it.getAnnotation(FeatureFlag::class.java) != null && it.kind == ElementKind.METHOD } | |
val packageName = processingEnv.elementUtils.getPackageOf(featureFlagGroupElement).toString() | |
generateImpl(packageName, featureFlagGroupElement, featureFlagElements) | |
} | |
return roundEnv.getElementsAnnotatedWith(FeatureFlagGroup::class.java).any { it.kind == ElementKind.INTERFACE } | |
} | |
private fun generateImpl( | |
packageName: String, | |
featureFlagGroupElement: Element, | |
featureFlagElements: List<Element> | |
) { | |
val generatedSourcesRoot = processingEnv.options[KAPT_KOTLIN_GENERATED_OPTION_NAME].orEmpty() | |
if (generatedSourcesRoot.isEmpty()) { | |
processingEnv.messager.printMessage( | |
Diagnostic.Kind.ERROR, | |
"Can't find the target directory for generated Kotlin files." | |
) | |
return | |
} | |
val implClassName = "${featureFlagGroupElement.simpleName}Impl" | |
val file = File(generatedSourcesRoot) | |
file.mkdir() | |
val className = ClassName( | |
(featureFlagGroupElement.enclosingElement as PackageElement).qualifiedName.toString(), | |
featureFlagGroupElement.simpleName.toString() | |
) | |
val funSpecs = featureFlagElements.map { | |
val executableElement = it as ExecutableElement | |
val featureFlagAnnotation = it.getAnnotation(FeatureFlag::class.java) | |
FunSpec.overriding(executableElement) | |
.addStatement("return ${featureFlagAnnotation.defaultValue}") | |
.build() | |
} | |
val defaultValuesMapCodeBlock = | |
featureFlagElements.foldIndexed(CodeBlock.builder().add("mapOf(\n")) { index, builder, element -> | |
val featureFlagAnnotation = element.getAnnotation(FeatureFlag::class.java) | |
builder.add("%S·to·${featureFlagAnnotation.defaultValue}", featureFlagAnnotation.key) | |
if (index < featureFlagElements.size - 1) { | |
builder.add(",\n") | |
} else { | |
builder.add("\n)") | |
} | |
builder | |
}.build() | |
FileSpec.builder(packageName, implClassName) | |
.addType( | |
TypeSpec.classBuilder(implClassName) | |
.addAnnotation( | |
AnnotationSpec.builder(Generated::class.java) | |
.addMember("value = [%S]", FeatureFlagCodegen::class.java.name) | |
.build() | |
) | |
.addKdoc(CodeBlock.of("Concrete implementation of [%T].", className)) | |
.primaryConstructor( | |
FunSpec.constructorBuilder() | |
.addAnnotation(ClassName("javax.inject", "Inject")) | |
.build() | |
) | |
.addSuperinterface(className) | |
.addFunctions(funSpecs) | |
.addType( | |
TypeSpec.companionObjectBuilder(null) | |
.addProperty( | |
PropertySpec.builder( | |
"defaultValues", | |
Map::class.asClassName() | |
.parameterizedBy(String::class.asClassName(), Boolean::class.asClassName()) | |
) | |
.initializer(defaultValuesMapCodeBlock) | |
.addKdoc("Default value map") | |
.build() | |
) | |
.build() | |
) | |
.build() | |
) | |
.build() | |
.writeTo(file) | |
} | |
} |
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package com.example.annotation.annotation | |
@Retention(AnnotationRetention.SOURCE) | |
@Target(AnnotationTarget.CLASS) | |
@MustBeDocumented | |
annotation class FeatureFlagGroup |
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package com.example.annotation.sample | |
import com.example.annotation.sample.example.MyFeatureFlagsA | |
import com.example.annotation.sample.example.MyFeatureFlagsAImpl | |
fun main() { | |
val featureFlagsA: MyFeatureFlagsA = MyFeatureFlagsAImpl() | |
val featureFlagsB: MyFeatureFlagsB = MyFeatureFlagsBImpl() | |
println("featureFlagsA.featureA1 = ${featureFlagsA.featureA1()}") | |
println("featureFlagsA.featureA2 = ${featureFlagsA.featureA2()}") | |
println("featureFlagsA.featureA3 = ${featureFlagsA.featureA3()}") | |
println("featureFlagsA.featureA4 = ${featureFlagsA.featureA4()}") | |
println("featureFlagsB.featureB1 = ${featureFlagsB.featureB1()}") | |
println("featureFlagsB.featureB2 = ${featureFlagsB.featureB2()}") | |
} |
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package com.example.annotation.sample | |
import com.example.annotation.annotation.FeatureFlag | |
import com.example.annotation.annotation.FeatureFlagGroup | |
@FeatureFlagGroup | |
interface MyFeatureFlagsA { | |
@FeatureFlag(key = "feature_a1", defaultValue = true) | |
fun featureA1(): Boolean | |
@FeatureFlag(key = "feature_a2", defaultValue = false) | |
fun featureA2(): Boolean | |
@FeatureFlag(key = "feature_a3", defaultValue = true) | |
fun featureA3(): Boolean | |
@FeatureFlag(key = "feature_a4", defaultValue = false) | |
fun featureA4(): Boolean | |
} |
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package com.example.annotation.sample | |
import com.example.annotation.annotation.FeatureFlag | |
import com.example.annotation.annotation.FeatureFlagGroup | |
@FeatureFlagGroup | |
interface MyFeatureFlagsB { | |
@FeatureFlag(key = "feature_b1", defaultValue = false) | |
fun featureB1(): Boolean | |
@FeatureFlag(key = "feature_b2", defaultValue = false) | |
fun featureB2(): Boolean | |
} |
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plugins { | |
id 'org.jetbrains.kotlin.jvm' version '1.3.61' | |
id 'org.jetbrains.kotlin.kapt' version '1.3.61' | |
} | |
group 'com.example.annotation' | |
version '1.0-SNAPSHOT' | |
repositories { | |
mavenCentral() | |
} | |
dependencies { | |
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8" | |
implementation project(':annotation') | |
kapt project(':codegen') | |
implementation "javax.inject:javax.inject:1" | |
} | |
compileKotlin { | |
kotlinOptions.jvmTarget = "1.8" | |
} | |
compileTestKotlin { | |
kotlinOptions.jvmTarget = "1.8" | |
} |
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