Deprecate JVM target 1.6

#KT-44650 Fixed

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.kt

@@ -71,7 +71,7 @@ class K2JVMCompilerArguments : CommonCompilerArguments() {
     @Argument(
         value = "-jvm-target",
         valueDescription = "<version>",
-        description = "Target version of the generated JVM bytecode (1.6, 1.8, 9, 10, 11, 12, 13, 14 or 15), default is 1.8"
+        description = "Target version of the generated JVM bytecode (1.6 (DEPRECATED), 1.8, 9, 10, 11, 12, 13, 14 or 15), default is 1.8"
     )
     var jvmTarget: String? by NullableStringFreezableVar(JvmTarget.DEFAULT.description)
 
@@ -448,6 +448,12 @@ class K2JVMCompilerArguments : CommonCompilerArguments() {
     )
     var enableJvmPreview: Boolean by FreezableVar(false)
 
+    @Argument(
+        value = "-Xsuppress-deprecated-jvm-target-warning",
+        description = "Suppress deprecation warning about deprecated JVM target versions"
+    )
+    var suppressDeprecatedJvmTargetWarning: Boolean by FreezableVar(false)
+
     override fun configureAnalysisFlags(collector: MessageCollector): MutableMap<AnalysisFlag<*>, Any> {
         val result = super.configureAnalysisFlags(collector)
         result[JvmAnalysisFlags.strictMetadataVersionSemantics] = strictMetadataVersionSemantics

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/jvmArguments.kt

@@ -29,6 +29,12 @@ fun CompilerConfiguration.setupJvmSpecificArguments(arguments: K2JVMCompilerArgu
         val jvmTarget = JvmTarget.fromString(arguments.jvmTarget!!)
         if (jvmTarget != null) {
             put(JVMConfigurationKeys.JVM_TARGET, jvmTarget)
+            if (jvmTarget == JvmTarget.JVM_1_6 && !arguments.suppressDeprecatedJvmTargetWarning) {
+                messageCollector.report(
+                    STRONG_WARNING,
+                    "JVM target 1.6 is deprecated and will be removed in a future release. Please migrate to JVM target 1.8 or above"
+                )
+            }
         } else {
             messageCollector.report(
                 ERROR, "Unknown JVM target version: ${arguments.jvmTarget}\n" +

compiler/testData/cli/jvm/extraHelp.out

@@ -118,6 +118,8 @@ where advanced options include:
   -Xsupport-compatqual-checker-framework-annotations=enable|disable
                              Specify behavior for Checker Framework compatqual annotations (NullableDecl/NonNullDecl).
                              Default value is 'enable'
+  -Xsuppress-deprecated-jvm-target-warning
+                             Suppress deprecation warning about deprecated JVM target versions
   -Xsuppress-missing-builtins-error
                              Suppress the "cannot access built-in declaration" error (useful with -no-stdlib)
   -Xuse-ir                   Use the IR backend

compiler/testData/cli/jvm/help.out

@@ -6,7 +6,7 @@ where possible options include:
   -include-runtime           Include Kotlin runtime into the resulting JAR
   -java-parameters           Generate metadata for Java 1.8 reflection on method parameters
   -jdk-home <path>           Include a custom JDK from the specified location into the classpath instead of the default JAVA_HOME
-  -jvm-target <version>      Target version of the generated JVM bytecode (1.6, 1.8, 9, 10, 11, 12, 13, 14 or 15), default is 1.8
+  -jvm-target <version>      Target version of the generated JVM bytecode (1.6 (DEPRECATED), 1.8, 9, 10, 11, 12, 13, 14 or 15), default is 1.8
   -module-name <name>        Name of the generated .kotlin_module file
   -no-jdk                    Don't automatically include the Java runtime into the classpath
   -no-reflect                Don't automatically include Kotlin reflection into the classpath

compiler/testData/cli/jvm/jvm6Target.args

@@ -0,0 +1,5 @@
+$TESTDATA_DIR$/jvm8Target.kt
+-d
+$TEMP_DIR$
+-jvm-target
+1.6

compiler/testData/cli/jvm/jvm6Target.out

@@ -0,0 +1,2 @@
+warning: JVM target 1.6 is deprecated and will be removed in a future release. Please migrate to JVM target 1.8 or above
+OK

compiler/testData/cli/jvm/jvmDefaultAll.out

@@ -1,2 +1,3 @@
+warning: JVM target 1.6 is deprecated and will be removed in a future release. Please migrate to JVM target 1.8 or above
 error: '-Xjvm-default=all' is only supported since JVM target 1.8. Recompile with '-jvm-target 1.8'
 COMPILATION_ERROR

compiler/tests-gen/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -536,6 +536,11 @@ public class CliTestGenerated extends AbstractCliTest {
             runTest("compiler/testData/cli/jvm/jsr305Warn.args");
         }
 
+        @TestMetadata("jvm6Target.args")
+        public void testJvm6Target() throws Exception {
+            runTest("compiler/testData/cli/jvm/jvm6Target.args");
+        }
+
         @TestMetadata("jvm8Target.args")
         public void testJvm8Target() throws Exception {
             runTest("compiler/testData/cli/jvm/jvm8Target.args");

compiler/tests/org/jetbrains/kotlin/jvm/compiler/CompileKotlinAgainstCustomBinariesTest.kt

@@ -22,6 +22,7 @@ import org.jetbrains.kotlin.codegen.forTestCompile.ForTestCompileRuntime
 import org.jetbrains.kotlin.codegen.inline.remove
 import org.jetbrains.kotlin.codegen.optimization.common.asSequence
 import org.jetbrains.kotlin.codegen.optimization.common.intConstant
+import org.jetbrains.kotlin.config.JvmTarget
 import org.jetbrains.kotlin.config.KotlinCompilerVersion
 import org.jetbrains.kotlin.config.KotlinCompilerVersion.TEST_IS_PRE_RELEASE_SYSTEM_PROPERTY
 import org.jetbrains.kotlin.config.LanguageFeature
@@ -43,6 +44,7 @@ import org.jetbrains.kotlin.test.util.RecursiveDescriptorComparatorAdaptor.valid
 import org.jetbrains.kotlin.utils.PathUtil
 import org.jetbrains.org.objectweb.asm.*
 import org.jetbrains.org.objectweb.asm.tree.AbstractInsnNode
+import org.jetbrains.org.objectweb.asm.tree.ClassNode
 import org.jetbrains.org.objectweb.asm.tree.MethodInsnNode
 import org.jetbrains.org.objectweb.asm.tree.MethodNode
 import java.io.ByteArrayInputStream
@@ -609,11 +611,13 @@ class CompileKotlinAgainstCustomBinariesTest : AbstractKotlinCompilerIntegration
     }
 
     fun testInlineAnonymousObjectWithDifferentTarget() {
-        val library = compileLibrary("library", additionalOptions = listOf("-jvm-target", "1.6"))
+        val library = compileLibrary("library", additionalOptions = listOf("-jvm-target", JvmTarget.JVM_1_8.description))
-        compileKotlin("source.kt", tmpdir, listOf(library), additionalOptions = listOf("-jvm-target", "1.8"))
+        compileKotlin("source.kt", tmpdir, listOf(library), additionalOptions = listOf("-jvm-target", JvmTarget.JVM_9.description))
-        val classLoader =
+        for (name in listOf("SourceKt", "SourceKt\$main\$\$inlined\$foo$1")) {
-            URLClassLoader(arrayOf(library.toURI().toURL(), tmpdir.toURI().toURL()), ForTestCompileRuntime.runtimeJarClassLoader())
+            val node = ClassNode()
-        classLoader.loadClass("SourceKt").getDeclaredMethod("main").invoke(null)
+            ClassReader(File(tmpdir, "$name.class").readBytes()).accept(node, 0)
+            assertEquals(JvmTarget.JVM_9.majorVersion, node.version)
+        }
     }
 
     fun testFirAgainstFir() {

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinJvmOptions.kt

@@ -23,7 +23,7 @@ interface KotlinJvmOptions  : org.jetbrains.kotlin.gradle.dsl.KotlinCommonOption
      var jdkHome: kotlin.String?
 
     /**
-     * Target version of the generated JVM bytecode (1.6, 1.8, 9, 10, 11, 12, 13, 14 or 15), default is 1.8
+     * Target version of the generated JVM bytecode (1.6 (DEPRECATED), 1.8, 9, 10, 11, 12, 13, 14 or 15), default is 1.8
      * Possible values: "1.6", "1.8", "9", "10", "11", "12", "13", "14", "15"
      * Default value: "1.8"
      */