Easy Way

1. Create a directory (e.g., demo_proj) for your project.

2. Run gradle init --type scala-library in terminal in the above directory.

3. Import the directory as a Gradle project in IntelliJ IDEA. Alternatively, you can add apply plugin: 'idea' into build.gradle and then run the command ./gradlew openIdea to import the directory as a Gradle project in Intellij IDEA.

Hard Way

1. Create a Gradle project in IntelliJ IDEA.

2. Create a directory named scala under src/main.

3. Mark the directory src/main/scala as source root directory.

4. Open build.gradle and change its content to the following.

   plugins {
       id 'scala'
   }
   apply plugin: 'idea'
   
   group 'net.legendu'
   version '1.0-SNAPSHOT'
   
   sourceCompatibility = 1.8
   
   dependencies {
       // Use Scala 2.12 in our library project
       implementation 'org.scala-lang:scala-library:2.12.7'
   
       // Use Scalatest for testing our library
       testImplementation 'junit:junit:4.12'
       testImplementation 'org.scalatest:scalatest_2.12:3.0.5'
   
       // Need scala-xml at test runtime
       testRuntimeOnly 'org.scala-lang.modules:scala-xml_2.12:1.1.1'
   }