[Build] Use 1.8 target version instead of 1.6 while using JPS build

buildSrc/src/main/kotlin/JvmToolchain.kt

@@ -43,6 +43,8 @@ fun Project.shouldOverrideObsoleteJdk(
 fun Project.configureJvmToolchain(
     jdkVersion: JdkMajorVersion
 ) {
+    @Suppress("NAME_SHADOWING")
+    val jdkVersion = chooseJdk18ForJpsBuild(jdkVersion)
     // Ensure java only modules also set default toolchain
     configureJavaOnlyToolchain(jdkVersion)
 
@@ -78,6 +80,8 @@ fun Project.configureJvmToolchain(
 fun Project.configureJavaOnlyToolchain(
     jdkVersion: JdkMajorVersion
 ) {
+    @Suppress("NAME_SHADOWING")
+    val jdkVersion = chooseJdk18ForJpsBuild(jdkVersion)
     plugins.withId("java-base") {
         val javaExtension = extensions.getByType<JavaPluginExtension>()
         if (shouldOverrideObsoleteJdk(jdkVersion)) {
@@ -100,6 +104,14 @@ fun Project.configureJavaOnlyToolchain(
     }
 }
 
+fun Project.chooseJdk18ForJpsBuild(jdkVersion: JdkMajorVersion): JdkMajorVersion {
+    return if (kotlinBuildProperties.isInJpsBuildIdeaSync) {
+        maxOf(jdkVersion, JdkMajorVersion.JDK_1_8)
+    } else {
+        jdkVersion
+    }
+}
+
 fun KotlinCompile.configureTaskToolchain(
     jdkVersion: JdkMajorVersion
 ) {
@@ -142,6 +154,12 @@ fun JavaCompile.configureTaskToolchain(
 fun Project.updateJvmTarget(
     jvmTarget: String
 ) {
+    @Suppress("NAME_SHADOWING")
+    val jvmTarget = if (kotlinBuildProperties.isInJpsBuildIdeaSync && jvmTarget == "1.6") {
+        "1.8"
+    } else {
+        jvmTarget
+    }
     // Java 9 tasks are exceptions that are configured in configureJava9Compilation
     tasks
         .withType<KotlinCompile>()