Gradle:

- default is now Java 8 toolchain (to fix Eclipse project import)
- `src/main/module-info` and `src/main/java9` are compiled with Java 11 toolchain (if global toolchain is Java 8)
- `src/main/module-info` and `src/main/java9` are no longer imported into Eclipse projects
- task `errorprone` now uses at least Java 11 toolchain

build.gradle.kts

@@ -16,6 +16,8 @@
 
 import net.ltgt.gradle.errorprone.errorprone
 
+
+// initialize version
 group = "com.formdev"
 version = property( if( hasProperty( "release" ) ) "flatlaf.releaseVersion" else "flatlaf.developmentVersion" ) as String
 
@@ -24,18 +26,16 @@ val pullRequestNumber = findProperty( "github.event.pull_request.number" )
 if( pullRequestNumber != null )
 	version = "PR-${pullRequestNumber}-SNAPSHOT"
 
-
-allprojects {
+// apply version to all subprojects
+subprojects {
 	version = rootProject.version
-
-	repositories {
-		mavenCentral()
-	}
 }
 
-// check required Java version
-if( JavaVersion.current() < JavaVersion.VERSION_1_8 )
-	throw RuntimeException( "Java 8 or later required (running ${System.getProperty( "java.version" )})" )
+
+// initialize toolchain version (default is Java 8)
+val toolchainJavaVersion: String by extra {
+	System.getProperty( "toolchain", "8" )
+}
 
 // log version, Gradle and Java versions
 println()
@@ -43,7 +43,7 @@ println( "----------------------------------------------------------------------
 println( "FlatLaf Version: ${version}" )
 println( "Gradle ${gradle.gradleVersion} at ${gradle.gradleHomeDir}" )
 println( "Java ${System.getProperty( "java.version" )}" )
-println( "Java toolchain ${System.getProperty( "toolchain", "11" )}" )
+println( "Java toolchain ${toolchainJavaVersion}" )
 println()
 
 
@@ -53,6 +53,10 @@ plugins {
 }
 
 allprojects {
+	repositories {
+		mavenCentral()
+	}
+
 	tasks {
 		withType<JavaCompile>().configureEach {
 			sourceCompatibility = "1.8"
@@ -139,6 +143,15 @@ allprojects {
 						)
 					}
 				}
+
+				// Error Prone requires at lease Java 11
+				val java = (project as ExtensionAware).extensions.getByName("java") as JavaPluginExtension
+				val javaToolchains = (project as ExtensionAware).extensions.getByName("javaToolchains") as JavaToolchainService
+				if( java.toolchain.languageVersion.get().asInt() < 11 ) {
+					javaCompiler.set( javaToolchains.compilerFor {
+						languageVersion.set( JavaLanguageVersion.of( 11 ) )
+					} )
+				}
 			}
 		}
 	}