androidx처럼 자동 마이그레이션이 안돼서 수동으로 해야함 (첨엔 귀찮지만 바꾸고 나면 문법이 틀린곳을 빌드해보기 전에 IDE에서 미리 알려줘서 좋음)

1. setting.gradle setting.gradle.kts로 이름 변경

rootProject.name = "Projectname"
include(":app")

2. build.gradle build.gradle.kts로 이름 변경

app 모듈의 build.gradle

plugins {
    id("com.android.application")
    id("kotlin-android")
}

android {
    compileSdkVersion(30)

    defaultConfig {
        applicationId = "android.milestone"
        minSdkVersion(23)
        targetSdkVersion(30)
        versionCode = 1
        versionName = "1.0"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        getByName("release") {
            isMinifyEnabled = false
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = "1.8"
    }
}

dependencies {
    implementation("org.jetbrains.kotlin:kotlin-stdlib:1.5.20")
    implementation("androidx.core:core-ktx:1.6.0")
    implementation("androidx.appcompat:appcompat:1.3.0")
    implementation("com.google.android.material:material:1.4.0")
    implementation("androidx.constraintlayout:constraintlayout:2.0.4")
    testImplementation("junit:junit:4.+")
    androidTestImplementation("androidx.test.ext:junit:1.1.3")
    androidTestImplementation("androidx.test.espresso:espresso-core:3.4.0")
}

프로젝트 최상위 build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        google()
        mavenCentral()
    }
    dependencies {
        classpath("com.android.tools.build:gradle:4.2.2")
        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.5.20")

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

task("clean", Delete::class) {
    delete = setOf(rootProject.buildDir)
}