[FE] Introduce a language feature entry for expect actual classes

^KT-62885 Fixed

compiler/config/src/org/jetbrains/kotlin/config/CommonConfigurationKeys.kt

@@ -108,3 +108,8 @@ var CompilerConfiguration.languageVersionSettings: LanguageVersionSettings
 
 val LanguageVersionSettings.isLibraryToSourceAnalysisEnabled: Boolean
     get() = getFlag(AnalysisFlags.libraryToSourceAnalysis)
+
+val LanguageVersionSettings.areExpectActualClassesStable: Boolean
+    get() {
+        return getFlag(AnalysisFlags.muteExpectActualClassesWarning) || supportsFeature(LanguageFeature.ExpectActualClasses)
+    }

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendMPPDiagnosticsWithLightTreeTestGenerated.java

@@ -151,6 +151,12 @@ public class FirOldFrontendMPPDiagnosticsWithLightTreeTestGenerated extends Abst
         runTest("compiler/testData/diagnostics/tests/multiplatform/expectActualClassesAreInBetaWarning.kt");
     }
 
+    @Test
+    @TestMetadata("expectActualClassesAreInBeta_suppressWarningWithLv.kt")
+    public void testExpectActualClassesAreInBeta_suppressWarningWithLv() throws Exception {
+        runTest("compiler/testData/diagnostics/tests/multiplatform/expectActualClassesAreInBeta_suppressWarningWithLv.kt");
+    }
+
     @Test
     @TestMetadata("expectDataObject.kt")
     public void testExpectDataObject() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendMPPDiagnosticsWithPsiTestGenerated.java

@@ -151,6 +151,12 @@ public class FirOldFrontendMPPDiagnosticsWithPsiTestGenerated extends AbstractFi
         runTest("compiler/testData/diagnostics/tests/multiplatform/expectActualClassesAreInBetaWarning.kt");
     }
 
+    @Test
+    @TestMetadata("expectActualClassesAreInBeta_suppressWarningWithLv.kt")
+    public void testExpectActualClassesAreInBeta_suppressWarningWithLv() throws Exception {
+        runTest("compiler/testData/diagnostics/tests/multiplatform/expectActualClassesAreInBeta_suppressWarningWithLv.kt");
+    }
+
     @Test
     @TestMetadata("expectDataObject.kt")
     public void testExpectDataObject() throws Exception {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirExpectActualClassifiersAreInBetaChecker.kt

@@ -5,8 +5,8 @@
 
 package org.jetbrains.kotlin.fir.analysis.checkers.declaration
 
-import org.jetbrains.kotlin.config.AnalysisFlags
 import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.config.areExpectActualClassesStable
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
@@ -18,7 +18,7 @@ import org.jetbrains.kotlin.fir.declarations.utils.isExpect
 object FirExpectActualClassifiersAreInBetaChecker : FirClassLikeChecker() {
     override fun check(declaration: FirClassLikeDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
         if (!context.languageVersionSettings.supportsFeature(LanguageFeature.MultiPlatformProjects)) return
-        if (context.languageVersionSettings.getFlag(AnalysisFlags.muteExpectActualClassesWarning)) return
+        if (context.languageVersionSettings.areExpectActualClassesStable) return
 
         if (declaration.isExpect || declaration.isActual) {
             reporter.reportOn(declaration.source, FirErrors.EXPECT_ACTUAL_CLASSIFIERS_ARE_IN_BETA_WARNING, context)

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExpectActualClassifiersAreInBetaChecker.kt

@@ -5,8 +5,8 @@
 
 package org.jetbrains.kotlin.resolve.checkers
 
-import org.jetbrains.kotlin.config.AnalysisFlags
 import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.config.areExpectActualClassesStable
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.ClassifierDescriptorWithTypeParameters
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
@@ -20,7 +20,7 @@ import org.jetbrains.kotlin.psi.KtTypeAlias
 object ExpectActualClassifiersAreInBetaChecker : DeclarationChecker {
     override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
         if (!context.languageVersionSettings.supportsFeature(LanguageFeature.MultiPlatformProjects)) return
-        if (context.languageVersionSettings.getFlag(AnalysisFlags.muteExpectActualClassesWarning)) return
+        if (context.languageVersionSettings.areExpectActualClassesStable) return
         if (descriptor !is TypeAliasDescriptor && descriptor !is ClassDescriptor) return
         check(declaration is KtClassOrObject || declaration is KtTypeAlias)
 

compiler/testData/diagnostics/tests/multiplatform/expectActualClassesAreInBeta_suppressWarningWithLv.kt

@@ -0,0 +1,51 @@
+// FIR_IDENTICAL
+// ENABLE_EXPECT_ACTUAL_CLASSES_WARNING
+// LANGUAGE: +ExpectActualClasses
+// MODULE: m1-common
+// FILE: common.kt
+
+expect class Clazz {
+    class Nested
+
+    fun memberFun()
+    val memberProp: Clazz
+}
+
+expect interface Interface
+
+expect object Object
+
+expect annotation class Annotation
+
+expect enum class Enum
+
+expect class ActualTypealias
+
+expect fun function()
+
+expect val property: Clazz
+
+// MODULE: m2-jvm()()(m1-common)
+// FILE: jvm.kt
+actual class Clazz {
+    actual class Nested
+
+    actual fun memberFun() {}
+    actual val memberProp: Clazz = null!!
+}
+
+actual interface Interface
+
+actual object Object
+
+actual annotation class Annotation
+
+actual enum class Enum
+
+actual typealias ActualTypealias = ActualTypealiasImpl
+
+class ActualTypealiasImpl
+
+actual fun function() {}
+
+actual val property: Clazz = null!!

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -23518,6 +23518,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/multiplatform/expectActualClassesAreInBetaWarning.kt");
             }
 
+            @Test
+            @TestMetadata("expectActualClassesAreInBeta_suppressWarningWithLv.kt")
+            public void testExpectActualClassesAreInBeta_suppressWarningWithLv() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/multiplatform/expectActualClassesAreInBeta_suppressWarningWithLv.kt");
+            }
+
             @Test
             @TestMetadata("expectDataObject.kt")
             public void testExpectDataObject() throws Exception {

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

@@ -319,6 +319,8 @@ enum class LanguageFeature(
 
     // End of 2.* language features --------------------------------------------------
 
+    ExpectActualClasses(sinceVersion = null), // KT-62885
+
     // Disabled for indefinite time. See KT-53751
     IgnoreNullabilityForErasedValueParameters(sinceVersion = null, kind = BUG_FIX),