Cleanup: LanguageFeature.defaultState -> LanguageFeature.isEnabledWithWarning

Review: https://jetbrains.team/p/kt/reviews/7418

`State` enum contains `DISABLED` item which is redundant for
`LanguageFeature`. It's redundant because `sinceVersion = null` is used
to express the same semantic.

I had to reorder some items in the enum because otherwise
`testLanguageFeatureOrder` fails. I could keep the same logic in
`testLanguageFeatureOrder` but I would need to make
`isEnabledWithWarning` public which I don't want to. Anyway, it's not
obvious what is more readable: keep `isEnabledWithWarning = true` items
at the end or at the beginning.

Also all effectively disabled features (`sinceVersion = null` or
`defaultState = State.DISABLED`) are now moved to the "Experimental"
section at the end which is obviously better.

compiler/tests/org/jetbrains/kotlin/code/CodeConformanceTest.kt

@@ -393,7 +393,7 @@ class CodeConformanceTest : TestCase() {
 
     fun testLanguageFeatureOrder() {
         val values = enumValues<LanguageFeature>()
-        val enabledFeatures = values.filter { it.sinceVersion != null && it.defaultState == LanguageFeature.State.ENABLED }
+        val enabledFeatures = values.filter { it.sinceVersion != null }
 
         if (enabledFeatures.sortedBy { it.sinceVersion!! } != enabledFeatures) {
             val (a, b) = enabledFeatures.zipWithNext().first { (a, b) -> a.sinceVersion!! > b.sinceVersion!! }

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -14,7 +14,7 @@ enum class LanguageFeature(
     val sinceVersion: LanguageVersion?,
     val sinceApiVersion: ApiVersion = ApiVersion.KOTLIN_1_0,
     val hintUrl: String? = null,
-    val defaultState: State = State.ENABLED,
+    internal val isEnabledWithWarning: Boolean = false,
     val kind: Kind = OTHER // NB: default value OTHER doesn't force pre-releaseness (see KDoc)
 ) {
     // Note: names of these entries are also used in diagnostic tests and in user-visible messages (see presentableText below)
@@ -42,6 +42,11 @@ enum class LanguageFeature(
     TypeInferenceOnGenericsForCallableReferences(KOTLIN_1_1),
     NoDelegationToJavaDefaultInterfaceMembers(KOTLIN_1_1),
     DefaultImportOfPackageKotlinComparisons(KOTLIN_1_1),
+    Coroutines(
+        KOTLIN_1_1, ApiVersion.KOTLIN_1_1,
+        "https://kotlinlang.org/docs/diagnostics/experimental-coroutines",
+        isEnabledWithWarning = true
+    ),
 
     // 1.2
 
@@ -93,6 +98,7 @@ enum class LanguageFeature(
     NewCapturedReceiverFieldNamingConvention(KOTLIN_1_3, kind = BUG_FIX),
     ExtendedMainConvention(KOTLIN_1_3),
     ExperimentalBuilderInference(KOTLIN_1_3),
+    InlineClasses(KOTLIN_1_3, isEnabledWithWarning = true, kind = UNSTABLE_FEATURE),
 
     // 1.4
 
@@ -123,7 +129,6 @@ enum class LanguageFeature(
     ProperFinally(KOTLIN_1_4, kind = BUG_FIX),
     AllowAssigningArrayElementsToVarargsInNamedFormForFunctions(KOTLIN_1_4),
     AllowNullOperatorsForResult(KOTLIN_1_4),
-    AllowResultInReturnType(KOTLIN_1_4, defaultState = State.DISABLED),
     PreferJavaFieldOverload(KOTLIN_1_4),
     AllowContractsForNonOverridableMembers(KOTLIN_1_4),
     AllowReifiedGenericsInContracts(KOTLIN_1_4),
@@ -133,7 +138,7 @@ enum class LanguageFeature(
     FunctionalInterfaceConversion(KOTLIN_1_4, kind = UNSTABLE_FEATURE),
     GenerateJvmOverloadsAsFinal(KOTLIN_1_4),
     MangleClassMembersReturningInlineClasses(KOTLIN_1_4),
-    ImproveReportingDiagnosticsOnProtectedMembersOfBaseClass(KOTLIN_1_4, kind = BUG_FIX, defaultState = State.ENABLED),
+    ImproveReportingDiagnosticsOnProtectedMembersOfBaseClass(KOTLIN_1_4, kind = BUG_FIX),
 
     NewInference(KOTLIN_1_4),
 
@@ -144,8 +149,6 @@ enum class LanguageFeature(
     FunctionReferenceWithDefaultValueAsOtherType(KOTLIN_1_4),
     OverloadResolutionByLambdaReturnType(KOTLIN_1_4),
     ContractsOnCallsWithImplicitReceiver(KOTLIN_1_4),
-    BooleanElvisBoundSmartCasts(KOTLIN_1_3, defaultState = State.DISABLED), // see KT-26357 for details
-    NewDataFlowForTryExpressions(KOTLIN_1_4, defaultState = State.DISABLED),
     // ^----------------------------------------------------------------------^
 
     // 1.5
@@ -156,35 +159,29 @@ enum class LanguageFeature(
     ProhibitVarargAsArrayAfterSamArgument(KOTLIN_1_5, kind = BUG_FIX),
     CorrectSourceMappingSyntax(KOTLIN_1_5, kind = UNSTABLE_FEATURE),
     ProperArrayConventionSetterWithDefaultCalls(KOTLIN_1_5, kind = OTHER),
-    DisableCompatibilityModeForNewInference(KOTLIN_1_5, defaultState = State.DISABLED),
+    DisableCompatibilityModeForNewInference(null),
-    AdaptedCallableReferenceAgainstReflectiveType(KOTLIN_1_5, defaultState = State.DISABLED),
+    AdaptedCallableReferenceAgainstReflectiveType(null),
     InferenceCompatibility(KOTLIN_1_5, kind = BUG_FIX),
     RequiredPrimaryConstructorDelegationCallInEnums(KOTLIN_1_5, kind = BUG_FIX),
     ApproximateAnonymousReturnTypesInPrivateInlineFunctions(KOTLIN_1_5, kind = BUG_FIX),
     ForbidReferencingToUnderscoreNamedParameterOfCatchBlock(KOTLIN_1_5, kind = BUG_FIX),
     UseCorrectExecutionOrderForVarargArguments(KOTLIN_1_5, kind = BUG_FIX),
     JvmRecordSupport(KOTLIN_1_5),
-    AllowNullOperatorsForResultAndResultReturnTypeByDefault(KOTLIN_1_5, defaultState = State.ENABLED),
+    AllowNullOperatorsForResultAndResultReturnTypeByDefault(KOTLIN_1_5),
     AllowSealedInheritorsInDifferentFilesOfSamePackage(KOTLIN_1_5),
     SealedInterfaces(KOTLIN_1_5),
     JvmIrEnabledByDefault(KOTLIN_1_5),
-    JvmInlineValueClasses(KOTLIN_1_5, defaultState = State.ENABLED, kind = OTHER),
+    JvmInlineValueClasses(KOTLIN_1_5, kind = OTHER),
-    SuspendFunctionsInFunInterfaces(KOTLIN_1_5, defaultState = State.ENABLED, kind = OTHER),
+    SuspendFunctionsInFunInterfaces(KOTLIN_1_5, kind = OTHER),
-    SamWrapperClassesAreSynthetic(KOTLIN_1_5, defaultState = State.ENABLED, kind = BUG_FIX),
+    SamWrapperClassesAreSynthetic(KOTLIN_1_5, kind = BUG_FIX),
     StrictOnlyInputTypesChecks(KOTLIN_1_5),
 
-    JsEnableExtensionFunctionInExternals(KOTLIN_1_5, defaultState = State.DISABLED, kind = OTHER),
-
-    // Disabled until the breaking change is approved by the committee, see KT-10884.
-    PackagePrivateFileClassesWithAllPrivateMembers(KOTLIN_1_5, defaultState = State.DISABLED),
-
     // 1.6
 
     ProhibitJvmFieldOnOverrideFromInterfaceInPrimaryConstructor(KOTLIN_1_6, kind = BUG_FIX),
     PrivateInFileEffectiveVisibility(KOTLIN_1_6, kind = BUG_FIX),
     ProhibitSelfCallsInNestedObjects(KOTLIN_1_6, kind = BUG_FIX),
     ProperCheckAnnotationsTargetInTypeUsePositions(KOTLIN_1_6, kind = BUG_FIX),
-
     SuspendFunctionAsSupertype(KOTLIN_1_6),
     UnrestrictedBuilderInference(KOTLIN_1_6),
     ClassTypeParameterAnnotations(KOTLIN_1_6),
@@ -257,7 +254,6 @@ enum class LanguageFeature(
     RefineTypeCheckingOnAssignmentsToJavaFields(KOTLIN_1_8, kind = BUG_FIX), // KT-46727
     RangeUntilOperator(KOTLIN_1_8), // KT-15613
     GenericInlineClassParameter(sinceVersion = KOTLIN_1_8, kind = UNSTABLE_FEATURE), // KT-32162
-    LightweightLambdas(KOTLIN_1_8, defaultState = State.DISABLED),
 
     // 1.9
 
@@ -277,7 +273,7 @@ enum class LanguageFeature(
     KeepNullabilityWhenApproximatingLocalType(KOTLIN_1_9, kind = BUG_FIX), // KT-53982
     SkipStandaloneScriptsInSourceRoots(KOTLIN_1_9, kind = OTHER), // KT-52525
     ModifierNonBuiltinSuspendFunError(KOTLIN_1_9, kind = BUG_FIX), // KT-49264
-    BreakContinueInInlineLambdas(KOTLIN_1_9, defaultState = State.ENABLED), // KT-1436
+    BreakContinueInInlineLambdas(KOTLIN_1_9), // KT-1436
     EnumEntries(KOTLIN_1_9, sinceApiVersion = ApiVersion.KOTLIN_1_8, kind = UNSTABLE_FEATURE), // KT-48872
     EnableDfaWarningsInK2(KOTLIN_1_9, kind = OTHER), // KT-50965
     ForbidSuperDelegationToAbstractFakeOverride(KOTLIN_1_9, kind = BUG_FIX), // KT-49017
@@ -299,28 +295,34 @@ enum class LanguageFeature(
     // However, later we encountered various situations when it works incorrectly, and decided to forbid them.
     // When this feature is disabled, various errors are reported which are related to these incorrect situations.
     // When this feature is enabled, no such errors are reported.
-    NoBuilderInferenceWithoutAnnotationRestriction(sinceVersion = null, kind = OTHER, defaultState = State.DISABLED),
+    NoBuilderInferenceWithoutAnnotationRestriction(sinceVersion = null, kind = OTHER),
 
     // Experimental features
 
-    Coroutines(
+    LightweightLambdas(null),
-        KOTLIN_1_1, ApiVersion.KOTLIN_1_1,
+    JsEnableExtensionFunctionInExternals(null, kind = OTHER),
-        "https://kotlinlang.org/docs/diagnostics/experimental-coroutines",
+    PackagePrivateFileClassesWithAllPrivateMembers(null), // Disabled until the breaking change is approved by the committee, see KT-10884.
-        State.ENABLED_WITH_WARNING
+    BooleanElvisBoundSmartCasts(null), // see KT-26357 for details
-    ),
+    NewDataFlowForTryExpressions(null),
-    MultiPlatformProjects(sinceVersion = null, defaultState = State.DISABLED),
+    AllowResultInReturnType(null),
-    InlineClasses(KOTLIN_1_3, defaultState = State.ENABLED_WITH_WARNING, kind = UNSTABLE_FEATURE),
+    MultiPlatformProjects(sinceVersion = null),
-    ProhibitComparisonOfIncompatibleClasses(sinceVersion = null, kind = BUG_FIX, defaultState = State.DISABLED),
+    ProhibitComparisonOfIncompatibleClasses(sinceVersion = null, kind = BUG_FIX),
-    ExplicitBackingFields(sinceVersion = null, defaultState = State.DISABLED, kind = UNSTABLE_FEATURE),
+    ExplicitBackingFields(sinceVersion = null, kind = UNSTABLE_FEATURE),
-    FunctionalTypeWithExtensionAsSupertype(sinceVersion = KOTLIN_1_6, defaultState = State.DISABLED),
+    FunctionalTypeWithExtensionAsSupertype(sinceVersion = null),
-    JsAllowInvalidCharsIdentifiersEscaping(sinceVersion = null, defaultState = State.DISABLED, kind = UNSTABLE_FEATURE),
+    JsAllowInvalidCharsIdentifiersEscaping(sinceVersion = null, kind = UNSTABLE_FEATURE),
-    JsAllowValueClassesInExternals(sinceVersion = null, defaultState = State.DISABLED, kind = UNSTABLE_FEATURE),
+    JsAllowValueClassesInExternals(sinceVersion = null, kind = UNSTABLE_FEATURE),
-    ContextReceivers(sinceVersion = null, defaultState = State.DISABLED),
+    ContextReceivers(sinceVersion = null),
-    ValueClasses(sinceVersion = null, defaultState = State.DISABLED, kind = UNSTABLE_FEATURE),
+    ValueClasses(sinceVersion = null, kind = UNSTABLE_FEATURE),
-    JavaSamConversionEqualsHashCode(sinceVersion = null, defaultState = State.DISABLED, kind = UNSTABLE_FEATURE),
+    JavaSamConversionEqualsHashCode(sinceVersion = null, kind = UNSTABLE_FEATURE),
-    UnitConversionsOnArbitraryExpressions(sinceVersion = null, defaultState = State.DISABLED),
+    UnitConversionsOnArbitraryExpressions(sinceVersion = null),
     ;
 
+    init {
+        if (sinceVersion == null && isEnabledWithWarning) {
+            error("$this: '${::isEnabledWithWarning.name}' has no effect if the feature is disabled by default")
+        }
+    }
+
     val presentableName: String
         // E.g. "DestructuringLambdaParameters" -> ["Destructuring", "Lambda", "Parameters"] -> "destructuring lambda parameters"
         get() = name.split("(?<!^)(?=[A-Z])".toRegex()).joinToString(separator = " ", transform = String::lowercase)
@@ -512,7 +514,7 @@ class LanguageVersionSettingsImpl @JvmOverloads constructor(
 
         val since = feature.sinceVersion
         if (since != null && languageVersion >= since && apiVersion >= feature.sinceApiVersion) {
-            return feature.defaultState
+            return if (feature.isEnabledWithWarning) LanguageFeature.State.ENABLED_WITH_WARNING else LanguageFeature.State.ENABLED
         }
 
         return LanguageFeature.State.DISABLED