Adding Kotlin compile support (#189)

* Adding kotlin support

* Configuring Kotlin spotless

* Configuring Kotlin for all kinds of subprojects

* Configuring Kotlin's apiVersion and using common Android Kotlin config block

build.gradle.kts

@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
+
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 buildscript {
     repositories {
@@ -16,6 +18,7 @@ plugins {
 }
 
 extra["java_version"] = JavaVersion.VERSION_1_8
+extra["kotlin_min_supported_version"] = KotlinVersion.KOTLIN_1_6
 
 allprojects {
     repositories {

buildSrc/build.gradle.kts

@@ -22,4 +22,5 @@ dependencies {
     implementation(libs.errorprone.plugin)
     implementation(libs.nullaway.plugin)
     implementation(libs.animalsniffer.plugin)
+    implementation(libs.kotlin.plugin)
 }

buildSrc/src/main/kotlin/otel.android-app-conventions.gradle.kts

@@ -1,8 +1,13 @@
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
+
 plugins {
     id("com.android.application")
+    id("org.jetbrains.kotlin.android")
     id("otel.errorprone-conventions")
 }
 
+val javaVersion = rootProject.extra["java_version"] as JavaVersion
+val minKotlinVersion = rootProject.extra["kotlin_min_supported_version"] as KotlinVersion
 android {
     namespace = "io.opentelemetry.android"
     compileSdk = (property("android.compileSdk") as String).toInt()
@@ -14,11 +19,16 @@ android {
     }
 
     compileOptions {
-        val javaVersion = rootProject.extra["java_version"] as JavaVersion
         sourceCompatibility(javaVersion)
         targetCompatibility(javaVersion)
         isCoreLibraryDesugaringEnabled = true
     }
+
+    kotlinOptions {
+        jvmTarget = javaVersion.toString()
+        apiVersion = minKotlinVersion.version
+        languageVersion = minKotlinVersion.version
+    }
 }
 
 val libs = extensions.getByType<VersionCatalogsExtension>().named("libs")

buildSrc/src/main/kotlin/otel.android-library-conventions.gradle.kts

@@ -1,8 +1,13 @@
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
+
 plugins {
     id("com.android.library")
+    id("org.jetbrains.kotlin.android")
     id("otel.errorprone-conventions")
 }
 
+val javaVersion = rootProject.extra["java_version"] as JavaVersion
+val minKotlinVersion = rootProject.extra["kotlin_min_supported_version"] as KotlinVersion
 android {
     compileSdk = (property("android.compileSdk") as String).toInt()
 
@@ -18,11 +23,16 @@ android {
     }
 
     compileOptions {
-        val javaVersion = rootProject.extra["java_version"] as JavaVersion
         sourceCompatibility(javaVersion)
         targetCompatibility(javaVersion)
         isCoreLibraryDesugaringEnabled = true
     }
+
+    kotlinOptions {
+        jvmTarget = javaVersion.toString()
+        apiVersion = minKotlinVersion.version
+        languageVersion = minKotlinVersion.version
+    }
 }
 
 tasks.withType<Test> {

buildSrc/src/main/kotlin/otel.java-library-conventions.gradle.kts

@@ -1,7 +1,10 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
 import ru.vyarus.gradle.plugin.animalsniffer.AnimalSniffer
 
 plugins {
     id("java-library")
+    id("org.jetbrains.kotlin.jvm")
     id("otel.errorprone-conventions")
     id("ru.vyarus.animalsniffer")
 }
@@ -15,11 +18,19 @@ val otelAndroidExtension =
     project.extensions.create("otelAndroid", OtelAndroidExtension::class.java)
 otelAndroidExtension.minSdk.convention((project.property("android.minSdk") as String).toInt())
 
+val javaVersion = rootProject.extra["java_version"] as JavaVersion
+val minKotlinVersion = rootProject.extra["kotlin_min_supported_version"] as KotlinVersion
 java {
-    val javaVersion = rootProject.extra["java_version"] as JavaVersion
     sourceCompatibility = javaVersion
     targetCompatibility = javaVersion
 }
+kotlin {
+    compilerOptions {
+        jvmTarget.set(JvmTarget.fromTarget(javaVersion.toString()))
+        apiVersion.set(minKotlinVersion)
+        languageVersion.set(minKotlinVersion)
+    }
+}
 
 val libs = extensions.getByType<VersionCatalogsExtension>().named("libs")
 dependencies {

buildSrc/src/main/kotlin/otel.spotless-conventions.gradle.kts

@@ -11,10 +11,10 @@ extensions.configure<SpotlessExtension>("spotless") {
         target("src/**/*.java")
     }
     plugins.withId("org.jetbrains.kotlin.jvm") {
-        kotlin {
-            ktlint()
-            licenseHeaderFile(rootProject.file("gradle/spotless.license.java"), "(package|import|public)")
-        }
+        configureKotlin(this@configure)
+    }
+    plugins.withId("org.jetbrains.kotlin.android") {
+        configureKotlin(this@configure)
     }
     kotlinGradle {
         ktlint()
@@ -37,3 +37,15 @@ extensions.configure<SpotlessExtension>("spotless") {
         endWithNewline()
     }
 }
+
+fun configureKotlin(
+    spotlessExtension: SpotlessExtension,
+) {
+    spotlessExtension.kotlin {
+        ktlint()
+        licenseHeaderFile(
+            rootProject.file("gradle/spotless.license.java")
+        )
+        target("src/**/*.kt")
+    }
+}

gradle/libs.versions.toml

@@ -9,6 +9,7 @@ byteBuddy = "1.14.10"
 okhttp = "4.12.0"
 spotless = "6.23.3"
 zipkin-reporter = "2.17.0"
+kotlin = "1.9.21"
 
 [libraries]
 opentelemetry-platform = { module = "io.opentelemetry.instrumentation:opentelemetry-instrumentation-bom-alpha", version.ref = "opentelemetry-alpha" }
@@ -55,6 +56,7 @@ nullaway-plugin = "net.ltgt.gradle:gradle-nullaway-plugin:1.6.0"
 animalsniffer-plugin = "ru.vyarus:gradle-animalsniffer-plugin:1.7.1"
 android-plugin = "com.android.tools.build:gradle:8.2.0"
 byteBuddy-plugin = { module = "net.bytebuddy:byte-buddy-gradle-plugin", version.ref = "byteBuddy" }
+kotlin-plugin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version.ref = "kotlin" }
 
 [bundles]
 mockito = ["mockito-core", "mockito-junit-jupiter"]