Extract modular Java toolchain version to a property

Author: ilya-g

build.gradle.kts

@@ -15,6 +15,7 @@ infra {
 }
 
 val mainJavaToolchainVersion by ext(project.property("java.mainToolchainVersion"))
+val modularJavaToolchainVersion by ext(project.property("java.modularToolchainVersion"))
 
 allprojects {
     repositories {

core/build.gradle.kts

@@ -19,6 +19,7 @@ base {
 }
 
 val mainJavaToolchainVersion: String by project
+val modularJavaToolchainVersion: String by project
 val serializationVersion: String by project
 
 java {
@@ -214,7 +215,7 @@ tasks {
         val targetDir = compileKotlinJvm.destinationDir.resolve("../java9/")
 
         // Use a Java 11 compiler for the module info.
-        javaCompiler.set(project.javaToolchains.compilerFor { languageVersion.set(JavaLanguageVersion.of(11)) })
+        javaCompiler.set(project.javaToolchains.compilerFor { languageVersion.set(JavaLanguageVersion.of(modularJavaToolchainVersion)) })
 
         // Always compile kotlin classes before the module descriptor.
         dependsOn(compileKotlinJvm)

gradle.properties

@@ -9,6 +9,7 @@ kotlinVersion=1.5.30
 serializationVersion=1.3.0
 
 java.mainToolchainVersion=8
+java.modularToolchainVersion=11
 
 kotlin.mpp.enableGranularSourceSetsMetadata=true
 kotlin.mpp.enableCompatibilityMetadataVariant=true