Prohibit JVM target 1.6

But still compile stdlib, reflect, kotlin.test and scripting runtimes
with JVM target 1.6 to simplify migration from Kotlin 1.6 to 1.7.

 #KT-45165 Fixed

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

@@ -37,7 +37,7 @@ open class DefaultValues(val defaultValue: String, val possibleValues: List<Stri
 
     object JvmTargetVersions : DefaultValues(
         "null",
-        JvmTarget.values().map { "\"${it.description}\"" }
+        JvmTarget.supportedValues().map { "\"${it.description}\"" }
     )
 
     object JsEcmaVersions : DefaultValues(

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

@@ -75,7 +75,7 @@ class K2JVMCompilerArguments : CommonCompilerArguments() {
     @Argument(
         value = "-jvm-target",
         valueDescription = "<version>",
-        description = "Target version of the generated JVM bytecode (1.6 (DEPRECATED), 1.8, 9, 10, ..., 18), default is 1.8"
+        description = "Target version of the generated JVM bytecode (1.8, 9, 10, ..., 18), default is 1.8"
     )
     var jvmTarget: String? by NullableStringFreezableVar(null)
 
@@ -466,7 +466,8 @@ Also sets `-jvm-target` value equal to the selected JDK version"""
 
     @Argument(
         value = "-Xsuppress-deprecated-jvm-target-warning",
-        description = "Suppress deprecation warning about deprecated JVM target versions"
+        description = "Suppress deprecation warning about deprecated JVM target versions.\n" +
+                "This option has no effect and will be deleted in a future version."
     )
     var suppressDeprecatedJvmTargetWarning: Boolean by FreezableVar(false)
 

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

@@ -56,10 +56,10 @@ fun CompilerConfiguration.setupJvmSpecificArguments(arguments: K2JVMCompilerArgu
         val jvmTarget = JvmTarget.fromString(jvmTargetValue)
         if (jvmTarget != null) {
             put(JVMConfigurationKeys.JVM_TARGET, jvmTarget)
-            if (jvmTarget == JvmTarget.JVM_1_6 && !arguments.suppressDeprecatedJvmTargetWarning) {
+            if (jvmTarget == JvmTarget.JVM_1_6 && !isJvmTarget6Allowed()) {
                 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"
+                    ERROR,
+                    "JVM target 1.6 is no longer supported. Please migrate to JVM target 1.8 or above"
                 )
             }
         } else {
@@ -353,3 +353,6 @@ private val CompilerConfiguration.messageCollector: MessageCollector
 
 private fun getJavaVersion(): Int =
     System.getProperty("java.specification.version")?.substringAfter('.')?.toIntOrNull() ?: 6
+
+private fun isJvmTarget6Allowed(): Boolean =
+    K2JVMCompiler::class.java.classLoader.getResource("META-INF/unsafe-allow-jvm6") != null

compiler/config.jvm/src/org/jetbrains/kotlin/config/JvmTarget.kt

@@ -55,5 +55,8 @@ enum class JvmTarget(
             return if (platformDescription != null) "JVM target $platformDescription"
             else "JVM bytecode version $majorVersion"
         }
+
+        fun supportedValues(): List<JvmTarget> =
+            values().asList() - JVM_1_6
     }
 }

compiler/testData/cli/jvm/extraHelp.out

@@ -131,7 +131,8 @@ where advanced options include:
                              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
+                             Suppress deprecation warning about deprecated JVM target versions.
+                             This option has no effect and will be deleted in a future version.
   -Xsuppress-missing-builtins-error
                              Suppress the "cannot access built-in declaration" error (useful with -no-stdlib)
   -Xtype-enhancement-improvements-strict-mode

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 (DEPRECATED), 1.8, 9, 10, ..., 18), default is 1.8
+  -jvm-target <version>      Target version of the generated JVM bytecode (1.8, 9, 10, ..., 18), 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.out

@@ -1,2 +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
+error: JVM target 1.6 is no longer supported. Please migrate to JVM target 1.8 or above
+COMPILATION_ERROR

compiler/testData/cli/jvm/jvmDefaultAll.out

@@ -1,3 +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: JVM target 1.6 is no longer supported. 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-common-jvm6/build.gradle.kts

@@ -8,6 +8,7 @@ project.updateJvmTarget("1.6")
 dependencies {
     api(kotlinStdlib())
     testApi(project(":kotlin-test:kotlin-test-jvm"))
+    kotlinCompilerClasspath(project(":libraries:tools:stdlib-compiler-classpath"))
 }
 
 sourceSets {