Enable -Xjvm-default=all

build.gradle

@@ -19,7 +19,7 @@ apply plugin: 'eclipse'
 apply plugin: 'maven-publish'
 apply plugin: 'kotlin'
 
-apply from: 'https://raw.githubusercontent.com/thedarkcolour/KotlinForForge/site/thedarkcolour/kotlinforforge/gradle/kff-3.0.0.gradle'
+apply from: "https://raw.githubusercontent.com/thedarkcolour/KotlinForForge/site/thedarkcolour/kotlinforforge/gradle/kff-${kotlin_for_forge_version}.gradle"
 
 version = mod_version
 group = 'ru.dbotthepony.mc' // http://maven.apache.org/guides/mini/guide-naming-conventions.html
@@ -35,6 +35,12 @@ exec {
     args 'shapenator.js'
 }
 
+tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
+    kotlinOptions {
+        freeCompilerArgs = ['-Xjvm-default=all']
+    }
+}
+
 test {
     useJUnitPlatform()
 }

gradle.properties

@@ -12,4 +12,5 @@ jupiter_version=5.8.2
 the_one_probe_version=5.0.1-5
 
 kotlin_version=1.6.0
-mod_version=1.0
+kotlin_for_forge_version=3.0.0
+mod_version=1.0