Upgrade Java language level to 11

build.gradle.kts

@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
 fun properties(key: String) = project.findProperty(key).toString()
 
 plugins {
@@ -19,9 +21,16 @@ intellij {
 }
 
 tasks {
-    withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile> {
-        kotlinOptions {
-            jvmTarget = "1.8"
+    // Set the JVM compatibility versions
+    properties("javaVersion").let {
+        withType<JavaCompile> {
+            sourceCompatibility = it
+            targetCompatibility = it
+        }
+        withType<KotlinCompile> {
+            kotlinOptions {
+                jvmTarget = it
+            }
         }
     }
 

gradle.properties

@@ -6,6 +6,9 @@ pluginName = filename_template
 pluginVersion = 1.2.0-213
 platformVersion = 2021.3
 
+# Java language level used to compile sources and to generate the files for - Java 11 is required since 2020.3
+javaVersion = 11
+
 gradleVersion = 7.3
 
 # Opt-out flag for bundling Kotlin standard library.