Add Kotlin code generation example

Author: yanex

gradle/kotlin-code-generation/.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea
+.DS_Store
+/build
+/example/build
+/annotation-processor/build
+/captures

gradle/kotlin-code-generation/annotation-processor/build.gradle

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+apply plugin: 'kotlin'
+
+dependencies {
+    compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+    compile 'com.github.yanex:takenoko:0.1'
+}

gradle/kotlin-code-generation/annotation-processor/src/main/java/TestAnnotationProcessor.kt

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+package org.kotlin.annotationProcessor
+
+import org.yanex.takenoko.*
+import java.io.File
+import javax.annotation.processing.*
+import javax.lang.model.SourceVersion
+import javax.lang.model.element.Element
+import javax.lang.model.element.TypeElement
+import javax.tools.Diagnostic.Kind.*
+
+@Target(AnnotationTarget.CLASS)
+annotation class TestAnnotation
+
+@SupportedSourceVersion(SourceVersion.RELEASE_8)
+@SupportedAnnotationTypes("org.kotlin.annotationProcessor.TestAnnotation")
+@SupportedOptions(TestAnnotationProcessor.KAPT_KOTLIN_GENERATED_OPTION_NAME)
+class TestAnnotationProcessor : AbstractProcessor() {
+    companion object {
+        const val KAPT_KOTLIN_GENERATED_OPTION_NAME = "kapt.kotlin.generated"
+    }
+
+    override fun process(annotations: MutableSet<out TypeElement>?, roundEnv: RoundEnvironment): Boolean {
+        val annotatedElements = roundEnv.getElementsAnnotatedWith(TestAnnotation::class.java)
+        if (annotatedElements.isEmpty()) return false
+
+        val kaptKotlinGeneratedDir = processingEnv.options[KAPT_KOTLIN_GENERATED_OPTION_NAME] ?: run {
+            processingEnv.messager.printMessage(ERROR, "Can't find the target directory for generated Kotlin files.")
+            return false
+        }
+
+        val generatedKtFile = kotlinFile("test.generated") {
+            for (element in annotatedElements) {
+                val typeElement = element.toTypeElementOrNull() ?: continue
+
+                property("simpleClassName") {
+                    receiverType(typeElement.qualifiedName.toString())
+                    getterExpression("this::class.java.simpleName")
+                }
+            }
+        }
+
+        File(kaptKotlinGeneratedDir, "testGenerated.kt").apply {
+            parentFile.mkdirs()
+            writeText(generatedKtFile.accept(PrettyPrinter(PrettyPrinterConfiguration())))
+        }
+
+        return true
+    }
+
+    fun Element.toTypeElementOrNull(): TypeElement? {
+        if (this !is TypeElement) {
+            processingEnv.messager.printMessage(ERROR, "Invalid element type, class expected", this)
+            return null
+        }
+
+        return this
+    }
+}

gradle/kotlin-code-generation/annotation-processor/src/main/resources/META-INF/services/javax.annotation.processing.Processor

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+org.kotlin.annotationProcessor.TestAnnotationProcessor

gradle/kotlin-code-generation/build.gradle

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+buildscript {
+    ext.kotlin_version = '1.1-SNAPSHOT'
+
+    repositories {
+        jcenter()
+        mavenLocal()
+    }
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+}
+
+allprojects {
+    repositories {
+        jcenter()
+        mavenLocal()
+        maven { url 'https://jitpack.io' }
+    }
+}

gradle/kotlin-code-generation/example/build.gradle

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+apply plugin: 'kotlin'
+apply plugin: 'kotlin-kapt'
+
+dependencies {
+	compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+
+    compile project(":annotation-processor")
+    kapt project(":annotation-processor")
+
+    testCompile 'junit:junit:4.12'
+}
+
+apply plugin: 'idea'
+
+idea {
+    module {
+        sourceDirs += files('build/generated/source/kapt/main', 'build/generated/source/kaptKotlin/main')
+        generatedSourceDirs += files('build/generated/source/kapt/main', 'build/generated/source/kaptKotlin/main')
+    }
+}

gradle/kotlin-code-generation/example/src/main/java/Example.kt

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+package org.kotlin.test
+
+import org.kotlin.annotationProcessor.TestAnnotation
+
+@TestAnnotation
+class SimpleClass

gradle/kotlin-code-generation/example/src/test/java/test.kt

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+package org.kotlin.test
+
+import org.junit.Test
+import org.junit.Assert.*
+import test.generated.simpleClassName
+
+class AnnotationTest {
+    @Test fun testSimple() {
+        assertEquals("SimpleClass", SimpleClass().simpleClassName)
+    }
+}

gradle/kotlin-code-generation/gradle.properties

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+kapt.verbose=true