Migrate to ForgeGradle-4.x

build.gradle

@@ -1,10 +1,10 @@
 buildscript {
     repositories {
-        maven { url = 'https://maven.minecraftforge.net/' }
         mavenCentral()
+        maven { url = "https://maven.minecraftforge.net/" }
     }
     dependencies {
-        classpath 'net.minecraftforge.gradle:ForgeGradle:3.+'
+        classpath group: 'net.minecraftforge.gradle', name: 'ForgeGradle', version: '4.1.+', changing: true
     }
 }
         
@@ -18,6 +18,9 @@ group = 'com.yourname.modid' // http://maven.apache.org/guides/mini/guide-naming
 archivesBaseName = 'modid'
 
 sourceCompatibility = targetCompatibility = compileJava.sourceCompatibility = compileJava.targetCompatibility = '1.8' // Need this here so eclipse task generates correctly.
+compileJava {
+    sourceCompatibility = targetCompatibility = '1.8'
+}
 
 minecraft {
     // The mappings can be changed at any time, and must be in the following format.
@@ -26,7 +29,7 @@ minecraft {
     // Use non-default mappings at your own risk. they may not always work.
     // Simply re-run your setup task after changing the mappings to update your workspace.
     //mappings channel: 'snapshot', version: '20171003-1.12'
-    mappings channel: 'snapshot', version: '20171003-1.12'
+    mappings channel: 'stable', version: '39-1.12'
     // makeObfSourceJar = false // an Srg named sources jar is made by default. uncomment this to disable.
     
     // accessTransformer = file('src/main/resources/META-INF/accesstransformer.cfg')
@@ -45,6 +48,7 @@ minecraft {
         }
 
         server {
+			workingDirectory project.file('run')
 
             // Recommended logging data for a userdev environment
             property 'forge.logging.markers', 'SCAN,REGISTRIES,REGISTRYDUMP'
@@ -55,6 +59,9 @@ minecraft {
     }
 }
 
+// Include resources generated by data generators.
+sourceSets.main.resources { srcDir 'src/generated/resources' }
+
 dependencies {
     // Specify the version of Minecraft to use, If this is any group other then 'net.minecraft' it is assumed
     // that the dep is a ForgeGradle 'patcher' dependency. And it's patches will be applied.
@@ -102,6 +109,18 @@ jar.finalizedBy('reobfJar')
 // However if you are in a multi-project build, dev time needs unobfed jar files, so you can delay the obfuscation until publishing by doing
 //publish.dependsOn('reobfJar')
 
+// workaround for userdev bug
+tasks.create("copyResourceToClasses", Copy.class) {
+    tasks.classes.dependsOn(it)
+    dependsOn(tasks.processResources)
+    onlyIf { gradle.taskGraph.hasTask(tasks.prepareRuns) }
+
+    into("$buildDir/classes/java/main")
+    // if you write @Mod class in kotlin, please use code below
+    // into("$buildDir/classes/kotlin/main")
+    from(tasks.processResources.destinationDir)
+}
+
 publishing {
     publications {
         mavenJava(MavenPublication) {

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,6 @@
+#Mon Sep 14 12:28:28 PDT 2015
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.9-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.8.1-bin.zip