[IR] Use common expect/actual matching algorithm in IR actualizer

^KT-58578 Fixed

compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/klib/compilerPipeline.kt

@@ -14,7 +14,6 @@ import org.jetbrains.kotlin.cli.common.fir.FirDiagnosticsCompilerResultsReporter
 import org.jetbrains.kotlin.cli.common.messages.AnalyzerWithCompilerReport
 import org.jetbrains.kotlin.cli.common.messages.MessageCollector
 import org.jetbrains.kotlin.config.CommonConfigurationKeys
-import org.jetbrains.kotlin.config.CompilerConfiguration
 import org.jetbrains.kotlin.config.languageVersionSettings
 import org.jetbrains.kotlin.constant.EvaluatedConstTracker
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
@@ -36,6 +35,7 @@ import org.jetbrains.kotlin.incremental.js.IncrementalDataProvider
 import org.jetbrains.kotlin.ir.backend.js.*
 import org.jetbrains.kotlin.ir.backend.js.lower.serialization.ir.JsManglerDesc
 import org.jetbrains.kotlin.ir.backend.js.lower.serialization.ir.JsManglerIr
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContextImpl
 import org.jetbrains.kotlin.ir.util.IrMessageLogger
 import org.jetbrains.kotlin.js.config.JSConfigurationKeys
 import org.jetbrains.kotlin.js.resolve.JsPlatformAnalyzerServices
@@ -217,6 +217,7 @@ fun transformFirToIr(
         visibilityConverter = Fir2IrVisibilityConverter.Default,
         kotlinBuiltIns = builtInsModule ?: DefaultBuiltIns.Instance,
         diagnosticReporter = diagnosticsReporter,
+        actualizerTypeContextProvider = ::IrTypeSystemContextImpl,
         fir2IrResultPostCompute = {
             (this.irModuleFragment.descriptor as? FirModuleDescriptor)?.let { it.allDependencyModules = librariesDescriptors }
         }

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/pipeline/convertToIr.kt

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.fir.pipeline
 import org.jetbrains.kotlin.backend.common.actualizer.IrActualizedResult
 import org.jetbrains.kotlin.backend.common.actualizer.IrActualizer
 import org.jetbrains.kotlin.backend.common.extensions.IrGenerationExtension
+import org.jetbrains.kotlin.backend.jvm.JvmIrTypeSystemContext
 import org.jetbrains.kotlin.backend.jvm.serialization.JvmIdSignatureDescriptor
 import org.jetbrains.kotlin.builtins.DefaultBuiltIns
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
@@ -20,10 +21,12 @@ import org.jetbrains.kotlin.fir.backend.jvm.FirJvmVisibilityConverter
 import org.jetbrains.kotlin.fir.declarations.FirFile
 import org.jetbrains.kotlin.fir.resolve.ScopeSession
 import org.jetbrains.kotlin.fir.signaturer.FirMangler
+import org.jetbrains.kotlin.ir.IrBuiltIns
 import org.jetbrains.kotlin.ir.backend.jvm.serialization.JvmDescriptorMangler
 import org.jetbrains.kotlin.ir.backend.jvm.serialization.JvmIrMangler
 import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 import org.jetbrains.kotlin.ir.declarations.impl.IrFactoryImpl
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContext
 import org.jetbrains.kotlin.ir.util.IdSignatureComposer
 import org.jetbrains.kotlin.ir.util.KotlinMangler
 
@@ -57,6 +60,7 @@ fun FirResult.convertToIrAndActualizeForJvm(
     visibilityConverter = FirJvmVisibilityConverter,
     diagnosticReporter = diagnosticReporter,
     kotlinBuiltIns = DefaultBuiltIns.Instance,
+    actualizerTypeContextProvider = ::JvmIrTypeSystemContext,
 )
 
 fun signatureComposerForJvmFir2Ir(generateSignatures: Boolean): IdSignatureComposer {
@@ -78,6 +82,7 @@ fun FirResult.convertToIrAndActualize(
     visibilityConverter: Fir2IrVisibilityConverter,
     kotlinBuiltIns: KotlinBuiltIns,
     diagnosticReporter: DiagnosticReporter,
+    actualizerTypeContextProvider: (IrBuiltIns) -> IrTypeSystemContext,
     fir2IrResultPostCompute: Fir2IrResult.() -> Unit = {},
 ): Fir2IrActualizedResult {
     val fir2IrResult: Fir2IrResult
@@ -140,6 +145,7 @@ fun FirResult.convertToIrAndActualize(
                 fir2IrResult.irModuleFragment,
                 commonIrOutputs.map { it.irModuleFragment },
                 diagnosticReporter,
+                actualizerTypeContextProvider(fir2IrResult.irModuleFragment.irBuiltins),
                 fir2IrConfiguration.languageVersionSettings
             )
         }

compiler/frontend.common/src/org/jetbrains/kotlin/diagnostics/DiagnosticReporter.kt

@@ -70,6 +70,13 @@ open class KtDiagnosticReporterWithContext(
             }
         }
 
+        fun <A : Any, B : Any, C : Any> report(factory: KtDiagnosticFactory3<A, B, C>, a: A, b: B, c: C) {
+            sourceElement?.let {
+                reportOn(it, factory, a, b, c, this)
+                checkAndCommitReportsOn(it, this)
+            }
+        }
+
         override fun equals(other: Any?): Boolean {
             if (this === other) return true
             if (other !is DiagnosticContextImpl) return false

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/CommonBackendErrors.kt

@@ -6,18 +6,24 @@
 package org.jetbrains.kotlin.backend.common
 
 import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.backend.common.BackendDiagnosticRenderers.INCOMPATIBILITY
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.diagnostics.KtDiagnosticFactoryToRendererMap
+import org.jetbrains.kotlin.diagnostics.error0
 import org.jetbrains.kotlin.diagnostics.error2
+import org.jetbrains.kotlin.diagnostics.error3
 import org.jetbrains.kotlin.diagnostics.rendering.BaseDiagnosticRendererFactory
 import org.jetbrains.kotlin.diagnostics.rendering.CommonRenderers.STRING
+import org.jetbrains.kotlin.diagnostics.rendering.Renderer
 import org.jetbrains.kotlin.diagnostics.rendering.Renderers.MODULE_WITH_PLATFORM
 import org.jetbrains.kotlin.diagnostics.rendering.RootDiagnosticRendererFactory
+import org.jetbrains.kotlin.resolve.multiplatform.ExpectActualCompatibility
 
 object CommonBackendErrors {
     val NO_ACTUAL_FOR_EXPECT by error2<PsiElement, String, ModuleDescriptor>()
     val MANY_INTERFACES_MEMBER_NOT_IMPLEMENTED by error2<PsiElement, String, String>()
     val MANY_IMPL_MEMBER_NOT_IMPLEMENTED by error2<PsiElement, String, String>()
+    val INCOMPATIBLE_MATCHING by error3<PsiElement, String, String, ExpectActualCompatibility.Incompatible<*>>()
 
     init {
         RootDiagnosticRendererFactory.registerFactory(KtDefaultCommonBackendErrorMessages)
@@ -44,5 +50,18 @@ object KtDefaultCommonBackendErrorMessages : BaseDiagnosticRendererFactory() {
             STRING,
             STRING,
         )
+        map.put(
+            CommonBackendErrors.INCOMPATIBLE_MATCHING,
+            "Expect declaration `{0}` doesn''t match actual `{1}` because {2}",
+            STRING,
+            STRING,
+            INCOMPATIBILITY
+        )
+    }
+}
+
+object BackendDiagnosticRenderers {
+    val INCOMPATIBILITY = Renderer<ExpectActualCompatibility.Incompatible<*>> {
+        it.reason ?: "<unknown>"
     }
 }

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/ActualFakeOverridesAdder.kt

@@ -8,13 +8,18 @@ package org.jetbrains.kotlin.backend.common.actualizer
 import org.jetbrains.kotlin.KtDiagnosticReporterWithImplicitIrBasedContext
 import org.jetbrains.kotlin.backend.common.CommonBackendErrors
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
+import org.jetbrains.kotlin.ir.IrBuiltIns
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContext
 import org.jetbrains.kotlin.ir.types.classifierOrFail
 import org.jetbrains.kotlin.ir.util.isInterface
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
+import org.jetbrains.kotlin.name.ClassId
+import org.jetbrains.kotlin.name.Name
 
 /**
  * It adds fake overrides to non-expect classes inside common or multi-platform module,
@@ -27,9 +32,11 @@ import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
  */
 internal class ActualFakeOverridesAdder(
     private val expectActualMap: Map<IrSymbol, IrSymbol>,
-    private val diagnosticsReporter: KtDiagnosticReporterWithImplicitIrBasedContext
+    private val expectToActualClassMap: Map<ClassId, IrClassSymbol>,
+    private val diagnosticsReporter: KtDiagnosticReporterWithImplicitIrBasedContext,
+    private val typeSystemContext: IrTypeSystemContext
 ) : IrElementVisitorVoid {
-    private val missingActualMembersMap = mutableMapOf<IrClass, MutableMap<String, MutableList<IrDeclaration>>>()
+    private val missingActualMembersMap = mutableMapOf<IrClass, FakeOverrideInfo>()
 
     override fun visitClass(declaration: IrClass) {
         extractMissingActualMembersFromSupertypes(declaration)
@@ -40,20 +47,20 @@ internal class ActualFakeOverridesAdder(
         element.acceptChildrenVoid(this)
     }
 
-    private fun extractMissingActualMembersFromSupertypes(klass: IrClass): Map<String, MutableList<IrDeclaration>> {
+    private fun extractMissingActualMembersFromSupertypes(klass: IrClass): FakeOverrideInfo {
         missingActualMembersMap[klass]?.let { return it }
 
-        val missingActualMembers = mutableMapOf<String, MutableList<IrDeclaration>>()
+        val missingActualMembers = FakeOverrideInfo()
         missingActualMembersMap[klass] = missingActualMembers
 
         // New members from supertypes are only relevant for not expect (ordinary) classes
         // New members from the current class are only relevant for actualized expect classes
 
-        val processedMembers = mutableMapOf<String, MutableList<IrDeclaration>>()
+        val processedMembers = FakeOverrideInfo()
         for (superType in klass.superTypes) {
             val membersFromSupertype = extractMissingActualMembersFromSupertypes(superType.classifierOrFail.owner as IrClass)
             if (!klass.isExpect) {
-                missingActualMembers.appendMissingMembersToNotExpectClass(klass, membersFromSupertype, processedMembers)
+                appendMissingMembersToNotExpectClass(missingActualMembers, klass, membersFromSupertype.allSymbols(), processedMembers)
             }
         }
 
@@ -64,22 +71,35 @@ internal class ActualFakeOverridesAdder(
         return missingActualMembers
     }
 
-    private fun MutableMap<String, MutableList<IrDeclaration>>.appendMissingMembersToNotExpectClass(
+    private fun appendMissingMembersToNotExpectClass(
+        fakeOverrideInfo: FakeOverrideInfo,
         klass: IrClass,
-        membersFromSupertype: Map<String, MutableList<IrDeclaration>>,
-        processedMembers: MutableMap<String, MutableList<IrDeclaration>>
+        membersFromSupertype: List<IrSymbol>,
+        processedMembers: FakeOverrideInfo
     ) {
-        for (memberFromSupertype in membersFromSupertype.flatMap { it.value }) {
+        for (symbolFromSupertype in membersFromSupertype) {
+            val memberFromSupertype = symbolFromSupertype.owner as IrDeclaration
             val newMember = createFakeOverrideMember(listOf(memberFromSupertype), klass)
-            val name = newMember.getFunctionOrPropertyName()
-            if (getMatches(name, newMember, expectActualMap).isEmpty()) {
+            val matchingFakeOverrides = collectActualCallablesMatchingToSpecificExpect(
+                newMember.symbol,
+                fakeOverrideInfo.getMembersForActual(newMember),
+                expectToActualClassMap,
+                typeSystemContext
+            )
+            if (matchingFakeOverrides.isEmpty()) {
                 processedMembers.addMember(memberFromSupertype as IrOverridableDeclaration<*>)
-                addMember(newMember)
+                fakeOverrideInfo.addMember(newMember)
                 klass.addMember(newMember)
             } else {
-                val baseMember = processedMembers.getMatches(name, newMember, expectActualMap).single()
+                val baseMembers = collectActualCallablesMatchingToSpecificExpect(
+                    newMember.symbol,
+                    processedMembers.getMembersForActual(newMember),
+                    expectToActualClassMap,
+                    typeSystemContext
+                )
+
                 val errorFactory =
-                    if ((baseMember.parent as IrClass).isInterface && (memberFromSupertype.parent as IrClass).isInterface)
+                    if (baseMembers.all { ((it.owner as IrDeclaration).parent as IrClass).isInterface } && (memberFromSupertype.parent as IrClass).isInterface)
                         CommonBackendErrors.MANY_INTERFACES_MEMBER_NOT_IMPLEMENTED
                     else
                         CommonBackendErrors.MANY_IMPL_MEMBER_NOT_IMPLEMENTED
@@ -92,7 +112,7 @@ internal class ActualFakeOverridesAdder(
         }
     }
 
-    private fun MutableMap<String, MutableList<IrDeclaration>>.appendMissingMembersFromActualizedExpectClass(
+    private fun FakeOverrideInfo.appendMissingMembersFromActualizedExpectClass(
         expectClass: IrClass,
         actualClass: IrClass,
     ) {
@@ -110,11 +130,31 @@ internal class ActualFakeOverridesAdder(
         }
     }
 
-    private fun MutableMap<String, MutableList<IrDeclaration>>.addMember(member: IrOverridableDeclaration<*>) {
-        getOrPut(member.getFunctionOrPropertyName()) { mutableListOf() }.add(member)
-    }
+    private class FakeOverrideInfo {
+        val functionsByName: MutableMap<Name, MutableList<IrSymbol>> = mutableMapOf()
+        val propertiesByName: MutableMap<Name, MutableList<IrSymbol>> = mutableMapOf()
 
-    private fun IrOverridableDeclaration<*>.getFunctionOrPropertyName(): String {
-        return (this as IrDeclarationWithName).name.asString() + (if (this is IrSimpleFunction) "()" else "")
+        fun allSymbols(): List<IrSymbol> {
+            return buildList {
+                functionsByName.values.flatMapTo(this) { it }
+                propertiesByName.values.flatMapTo(this) { it }
+            }
+        }
+
+        private fun getCorrespondingMap(member: IrOverridableDeclaration<*>): MutableMap<Name, MutableList<IrSymbol>> {
+            return when (member) {
+                is IrFunction -> functionsByName
+                is IrProperty -> propertiesByName
+                else -> error("Unsupported declaration type: $member")
+            }
+        }
+
+        fun addMember(member: IrOverridableDeclaration<*>) {
+            getCorrespondingMap(member).getOrPut(member.name) { mutableListOf() } += member.symbol
+        }
+
+        fun getMembersForActual(actualMember: IrOverridableDeclaration<*>): List<IrSymbol> {
+            return getCorrespondingMap(actualMember)[actualMember.name].orEmpty()
+        }
     }
-}
+}

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/ExpectActualCollector.kt

@@ -8,66 +8,97 @@ package org.jetbrains.kotlin.backend.common.actualizer
 import org.jetbrains.kotlin.KtDiagnosticReporterWithImplicitIrBasedContext
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
-import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
-import org.jetbrains.kotlin.ir.symbols.IrSymbol
+import org.jetbrains.kotlin.ir.symbols.*
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContext
 import org.jetbrains.kotlin.ir.types.classifierOrFail
-import org.jetbrains.kotlin.ir.util.isFakeOverride
-import org.jetbrains.kotlin.ir.util.kotlinFqName
+import org.jetbrains.kotlin.ir.util.callableId
+import org.jetbrains.kotlin.ir.util.classIdOrFail
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.mpp.DeclarationSymbolMarker
+import org.jetbrains.kotlin.name.CallableId
+import org.jetbrains.kotlin.name.ClassId
+import org.jetbrains.kotlin.resolve.calls.mpp.AbstractExpectActualCompatibilityChecker
+import org.jetbrains.kotlin.resolve.multiplatform.ExpectActualCompatibility
 
+/**
+ * This class is used to collect mapping between all expect and actuals declarations, which are declared in passed module fragments
+ * It does not process any declarations which may appear after actualization of supertypes (like fake-overrides in classes with
+ *   expect supertypes)
+ *
+ * The main method of this class, `collect` returns a pair of two values:
+ * - `expectToActualMap` is the main storage of all mapped declarations. Key is symbol of expect declaration and the value is symbol of
+ *     corresponding actual declaration
+ * - `classActualizationInfo` is a storage which keeps information about types (class) actualization, which can be used later for type
+ *     refinement if needed
+ *
+ * If some declarations didn't match (or there was missing/actual) then corresponding declarations won't be stored in `expectToActualMap`.
+ *   Instead of that an error will be reported to `diagnosticReporter`
+ */
 internal class ExpectActualCollector(
     private val mainFragment: IrModuleFragment,
     private val dependentFragments: List<IrModuleFragment>,
-    private val diagnosticsReporter: KtDiagnosticReporterWithImplicitIrBasedContext
+    private val typeSystemContext: IrTypeSystemContext,
+    private val diagnosticsReporter: KtDiagnosticReporterWithImplicitIrBasedContext,
 ) {
-    fun collect(): MutableMap<IrSymbol, IrSymbol> {
+    data class Result(val expectToActualMap: MutableMap<IrSymbol, IrSymbol>, val classActualizationInfo: ClassActualizationInfo)
+
+    fun collect(): Result {
         val result = mutableMapOf<IrSymbol, IrSymbol>()
         // Collect and link classes at first to make it possible to expand type aliases on the members linking
-        val (actualMembers, expectActualTypeAliasMap) = result.appendExpectActualClassMap()
-        result.appendExpectActualMemberMap(actualMembers, expectActualTypeAliasMap)
-        return result
+        val actualDeclarations = collectActualDeclarations()
+        matchAllExpectDeclarations(result, actualDeclarations)
+        return Result(result, actualDeclarations)
     }
 
-    private fun MutableMap<IrSymbol, IrSymbol>.appendExpectActualClassMap(): Pair<List<IrDeclarationBase>, Map<FqName, FqName>> {
-        val actualClasses = mutableMapOf<String, IrClassSymbol>()
-        // There is no list for builtins declarations; that's why they are being collected from typealiases
-        val actualMembers = mutableListOf<IrDeclarationBase>()
-        val expectActualTypeAliasMap = mutableMapOf<FqName, FqName>() // It's used to link members from expect class that have typealias actual
-
+    private fun collectActualDeclarations(): ClassActualizationInfo {
         val fragmentsWithActuals = dependentFragments.drop(1) + mainFragment
-        val actualClassesAndMembersCollector = ActualClassesAndMembersCollector(actualClasses, actualMembers, expectActualTypeAliasMap)
-        fragmentsWithActuals.forEach { actualClassesAndMembersCollector.collect(it) }
-
-        val linkCollector = ClassLinksCollector(this, actualClasses, expectActualTypeAliasMap, diagnosticsReporter)
-        dependentFragments.forEach { linkCollector.visitModuleFragment(it) }
-
-        return actualMembers to expectActualTypeAliasMap
+        return ActualDeclarationsCollector.collectActualsFromFragments(fragmentsWithActuals)
     }
 
-    private fun MutableMap<IrSymbol, IrSymbol>.appendExpectActualMemberMap(
-        actualMembers: List<IrDeclarationBase>,
-        expectActualTypeAliasMap: Map<FqName, FqName>
+    private fun matchAllExpectDeclarations(
+        destination: MutableMap<IrSymbol, IrSymbol>,
+        classActualizationInfo: ClassActualizationInfo,
     ) {
-        val actualMembersMap = mutableMapOf<String, MutableList<IrDeclarationBase>>()
-        for (actualMember in actualMembers) {
-            actualMembersMap.getOrPut(generateIrElementFullNameFromExpect(actualMember, expectActualTypeAliasMap)) { mutableListOf() }
-                .add(actualMember)
-        }
-        val collector = MemberLinksCollector(this, actualMembersMap, expectActualTypeAliasMap, diagnosticsReporter)
-        dependentFragments.forEach { collector.visitModuleFragment(it) }
+        val linkCollector = ExpectActualLinkCollector(destination, classActualizationInfo, typeSystemContext, diagnosticsReporter)
+        dependentFragments.forEach { linkCollector.visitModuleFragment(it) }
     }
 }
 
-private class ActualClassesAndMembersCollector(
-    private val actualClasses: MutableMap<String, IrClassSymbol>,
-    private val actualMembers: MutableList<IrDeclarationBase>,
-    private val expectActualTypeAliasMap: MutableMap<FqName, FqName>
+internal data class ClassActualizationInfo(
+    // mapping from classId of actual class/typealias to itself/typealias expansion
+    val actualClasses: Map<ClassId, IrClassSymbol>,
+    // mapping from classId to actual typealias
+    val actualTypeAliases: Map<ClassId, IrTypeAliasSymbol>,
+    val actualTopLevels: Map<CallableId, List<IrDeclarationWithName>>,
 ) {
+    fun getActualWithoutExpansion(classId: ClassId): IrSymbol? {
+        return actualTypeAliases[classId] ?: actualClasses[classId]
+    }
+}
+
+private class ActualDeclarationsCollector {
+    companion object {
+        fun collectActualsFromFragments(fragments: List<IrModuleFragment>): ClassActualizationInfo {
+            val collector = ActualDeclarationsCollector()
+            for (fragment in fragments) {
+                collector.collect(fragment)
+            }
+            return ClassActualizationInfo(
+                collector.actualClasses,
+                collector.actualTypeAliasesWithoutExpansion,
+                collector.actualTopLevels
+            )
+        }
+    }
+
+    private val actualClasses: MutableMap<ClassId, IrClassSymbol> = mutableMapOf()
+    private val actualTypeAliasesWithoutExpansion: MutableMap<ClassId, IrTypeAliasSymbol> = mutableMapOf()
+    private val actualTopLevels: MutableMap<CallableId, MutableList<IrDeclarationWithName>> = mutableMapOf()
+
     private val visitedActualClasses = mutableSetOf<IrClass>()
 
-    fun collect(element: IrElement) {
+    private fun collect(element: IrElement) {
         when (element) {
             is IrModuleFragment -> {
                 for (file in element.files) {
@@ -77,16 +108,18 @@ private class ActualClassesAndMembersCollector(
             is IrTypeAlias -> {
                 if (!element.isActual) return
 
+                val classId = element.classIdOrFail
                 val expandedTypeSymbol = element.expandedType.classifierOrFail as IrClassSymbol
-                addActualClass(element, expandedTypeSymbol)
-                collect(expandedTypeSymbol.owner)
 
-                expectActualTypeAliasMap[element.kotlinFqName] = expandedTypeSymbol.owner.kotlinFqName
+                actualClasses[classId] = expandedTypeSymbol
+                actualTypeAliasesWithoutExpansion[classId] = element.symbol
+
+                collect(expandedTypeSymbol.owner)
             }
             is IrClass -> {
                 if (element.isExpect || !visitedActualClasses.add(element)) return
 
-                addActualClass(element, element.symbol)
+                actualClasses[element.classIdOrFail] = element.symbol
                 for (declaration in element.declarations) {
                     collect(declaration)
                 }
@@ -97,101 +130,99 @@ private class ActualClassesAndMembersCollector(
                 }
             }
             is IrEnumEntry -> {
-                actualMembers.add(element) // If enum entry is located inside expect enum, then this code is not executed
+                recordActualCallable(element, element.callableId) // If enum entry is located inside expect enum, then this code is not executed
             }
             is IrProperty -> {
                 if (element.isExpect) return
-                actualMembers.add(element)
+                recordActualCallable(element, element.callableId)
             }
             is IrFunction -> {
                 if (element.isExpect) return
-                actualMembers.add(element)
+                recordActualCallable(element, element.callableId)
             }
         }
     }
 
-    private fun addActualClass(classOrTypeAlias: IrElement, classSymbol: IrClassSymbol) {
-        actualClasses[generateActualIrClassOrTypeAliasFullName(classOrTypeAlias)] = classSymbol
+    private fun recordActualCallable(callableDeclaration: IrDeclarationWithName, callableId: CallableId) {
+        if (callableId.classId == null) {
+            actualTopLevels
+                .getOrPut(callableId) { mutableListOf() }
+                .add(callableDeclaration)
+        }
     }
 }
 
-private class ClassLinksCollector(
-    private val expectActualMap: MutableMap<IrSymbol, IrSymbol>,
-    private val actualClasses: Map<String, IrClassSymbol>,
-    private val expectActualTypeAliasMap: Map<FqName, FqName>,
-    private val diagnosticsReporter: KtDiagnosticReporterWithImplicitIrBasedContext
+private class ExpectActualLinkCollector(
+    private val destination: MutableMap<IrSymbol, IrSymbol>,
+    private val classActualizationInfo: ClassActualizationInfo,
+    typeSystemContext: IrTypeSystemContext,
+    private val diagnosticsReporter: KtDiagnosticReporterWithImplicitIrBasedContext,
 ) : IrElementVisitorVoid {
+    private val context = MatchingContext(typeSystemContext)
+
+    override fun visitFunction(declaration: IrFunction) {
+        if (declaration.isExpect) {
+            matchExpectCallable(declaration, declaration.callableId)
+        }
+    }
+
+    override fun visitProperty(declaration: IrProperty) {
+        if (declaration.isExpect) {
+            matchExpectCallable(declaration, declaration.callableId)
+        }
+    }
+
+    private fun matchExpectCallable(declaration: IrDeclarationWithName, callableId: CallableId) {
+        val actualSymbols = classActualizationInfo.actualTopLevels[callableId]?.map { it.symbol }.orEmpty()
+        matchExpectDeclaration(declaration.symbol, actualSymbols)
+    }
+
     override fun visitClass(declaration: IrClass) {
         if (!declaration.isExpect) return
+        val classId = declaration.classIdOrFail
+        val expectClassSymbol = declaration.symbol
+        val actualClassLikeSymbol = classActualizationInfo.getActualWithoutExpansion(classId)
+        matchExpectDeclaration(expectClassSymbol, listOfNotNull(actualClassLikeSymbol))
+    }
 
-        val actualClassSymbol = actualClasses[generateIrElementFullNameFromExpect(declaration, expectActualTypeAliasMap)]
-        if (actualClassSymbol != null) {
-            expectActualMap[declaration.symbol] = actualClassSymbol
-            expectActualMap.appendTypeParametersMap(declaration, actualClassSymbol.owner)
-        } else if (!declaration.containsOptionalExpectation()) {
-            diagnosticsReporter.reportMissingActual(declaration)
-        }
-
-        visitElement(declaration)
+    private fun matchExpectDeclaration(expectSymbol: IrSymbol, actualSymbols: List<IrSymbol>) {
+        AbstractExpectActualCompatibilityChecker.matchSingleExpectTopLevelDeclarationAgainstPotentialActuals(
+            expectSymbol,
+            actualSymbols,
+            context
+        )
     }
 
     override fun visitElement(element: IrElement) {
         element.acceptChildrenVoid(this)
     }
-}
 
-private class MemberLinksCollector(
-    private val expectActualMap: MutableMap<IrSymbol, IrSymbol>,
-    private val actualMembers: Map<String, List<IrDeclarationBase>>,
-    private val typeAliasMap: Map<FqName, FqName>,
-    private val diagnosticsReporter: KtDiagnosticReporterWithImplicitIrBasedContext
-) : IrElementVisitorVoid {
-    override fun visitFunction(declaration: IrFunction) {
-        if (declaration.isExpect) addLink(declaration)
-    }
+    private inner class MatchingContext(
+        typeSystemContext: IrTypeSystemContext,
+    ) : IrExpectActualMatchingContext(typeSystemContext, classActualizationInfo.actualClasses) {
+        override fun onMatchedClasses(expectClassSymbol: IrClassSymbol, actualClassSymbol: IrClassSymbol) {
+            destination[expectClassSymbol] = actualClassSymbol
+            recordActualForExpectDeclaration(expectClassSymbol, actualClassSymbol, destination)
+        }
 
-    override fun visitProperty(declaration: IrProperty) {
-        if (declaration.isExpect) addLink(declaration)
-    }
+        override fun onMatchedCallables(expectSymbol: IrSymbol, actualSymbol: IrSymbol) {
+            recordActualForExpectDeclaration(expectSymbol, actualSymbol, destination)
+        }
 
-    override fun visitEnumEntry(declaration: IrEnumEntry) {
-        if ((declaration.parent as IrClass).isExpect) addLink(declaration)
-    }
-
-    private fun addLink(expectDeclaration: IrDeclarationBase) {
-        val actualMemberMatches = actualMembers.getMatches(expectDeclaration, expectActualMap, typeAliasMap)
-        when {
-            actualMemberMatches.size == 1 -> {
-                expectActualMap.addLink(expectDeclaration, actualMemberMatches.single())
+        override fun onMismatchedMembersFromClassScope(
+            expectSymbol: DeclarationSymbolMarker,
+            actualSymbolsByIncompatibility: Map<ExpectActualCompatibility.Incompatible<*>, List<DeclarationSymbolMarker>>,
+        ) {
+            require(expectSymbol is IrSymbol)
+            if (actualSymbolsByIncompatibility.isEmpty() && !expectSymbol.owner.containsOptionalExpectation()) {
+                diagnosticsReporter.reportMissingActual(expectSymbol)
             }
-            actualMemberMatches.size > 1 -> {
-                // TODO: report AMBIGUOUS_ACTUALS here, see KT-57932
-            }
-            (expectDeclaration.parent as? IrClass)?.isExpect == false && expectDeclaration.isFakeOverride -> {
-                // Remaining expect fake override members from not expect classes will be actualized in FakeOverridesTransformer
-                // It occurs in a separated step because they require filled expectActualMap for members from expect classes
-            }
-            else -> {
-                if (shouldReportMissingActual(expectDeclaration)) {
-                    diagnosticsReporter.reportMissingActual(expectDeclaration)
+            for ((incompatibility, actualMemberSymbols) in actualSymbolsByIncompatibility) {
+                for (actualSymbol in actualMemberSymbols) {
+                    require(actualSymbol is IrSymbol)
+                    diagnosticsReporter.reportIncompatibleExpectActual(expectSymbol, actualSymbol, incompatibility)
                 }
             }
         }
     }
-
-    private fun shouldReportMissingActual(declaration: IrDeclarationBase): Boolean {
-        return !declaration.parent.containsOptionalExpectation() && !(declaration is IrConstructor && declaration.isPrimary)
-    }
-
-    override fun visitElement(element: IrElement) {
-        element.acceptChildrenVoid(this)
-    }
 }
-
-fun MutableMap<IrSymbol, IrSymbol>.appendTypeParametersMap(
-    expectTypeParametersContainer: IrTypeParametersContainer,
-    actualTypeParametersContainer: IrTypeParametersContainer
-) {
-    expectTypeParametersContainer.typeParameters.zip(actualTypeParametersContainer.typeParameters)
-        .forEach { (expectTypeParameter, actualTypeParameter) -> this[expectTypeParameter.symbol] = actualTypeParameter.symbol }
-}

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/FakeOverridesActualizer.kt

@@ -47,11 +47,11 @@ internal class FakeOverridesActualizer(private val expectActualMap: MutableMap<I
             val actualizedOverrides = overriddenSymbols.map { (it.owner as IrDeclaration).actualize() }
             val actualFakeOverride = createFakeOverrideMember(actualizedOverrides, parent as IrClass)
 
-            expectActualMap.addLink(this as IrDeclarationBase, actualFakeOverride)
+            recordActualForExpectDeclaration(this.symbol, actualFakeOverride.symbol, expectActualMap)
 
             return actualFakeOverride
         }
 
         klass.declarations.transformInPlace { if (it.isExpect && it.isFakeOverride) it.actualize() else it }
     }
-}
+}

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/IrActualizer.kt

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContext
 import org.jetbrains.kotlin.ir.util.DeepCopyTypeRemapper
 
 data class IrActualizedResult(val actualizedExpectDeclarations: List<IrDeclaration>)
@@ -19,15 +20,17 @@ object IrActualizer {
         mainFragment: IrModuleFragment,
         dependentFragments: List<IrModuleFragment>,
         diagnosticReporter: DiagnosticReporter,
+        typeSystemContext: IrTypeSystemContext,
         languageVersionSettings: LanguageVersionSettings
     ): IrActualizedResult {
         val ktDiagnosticReporter = KtDiagnosticReporterWithImplicitIrBasedContext(diagnosticReporter, languageVersionSettings)
 
         // The ir modules processing is performed phase-to-phase:
         //   1. Collect expect-actual links for classes and their members from dependent fragments
-        val expectActualMap = ExpectActualCollector(
+        val (expectActualMap, actualDeclarations) = ExpectActualCollector(
             mainFragment,
             dependentFragments,
+            typeSystemContext,
             ktDiagnosticReporter
         ).collect()
 
@@ -44,7 +47,9 @@ object IrActualizer {
         //      taken from these non-expect classes actualized super classes.
         ActualFakeOverridesAdder(
             expectActualMap,
-            ktDiagnosticReporter
+            actualDeclarations.actualClasses,
+            ktDiagnosticReporter,
+            typeSystemContext
         ).apply { dependentFragments.forEach { visitModuleFragment(it) } }
 
         //   5. Copy and actualize function parameter default values from expect functions
@@ -91,4 +96,4 @@ object IrActualizer {
     private fun mergeIrFragments(mainFragment: IrModuleFragment, dependentFragments: List<IrModuleFragment>) {
         mainFragment.files.addAll(0, dependentFragments.flatMap { it.files })
     }
-}
+}

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/IrActualizerUtils.kt

@@ -13,182 +13,89 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.builders.declarations.buildFun
 import org.jetbrains.kotlin.ir.builders.declarations.buildProperty
 import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrPropertySymbol
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
-import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
-import org.jetbrains.kotlin.ir.types.IrDynamicType
-import org.jetbrains.kotlin.ir.types.classifierOrFail
-import org.jetbrains.kotlin.ir.types.isNullable
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContext
 import org.jetbrains.kotlin.ir.util.*
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.StandardClassIds
+import org.jetbrains.kotlin.name.ClassId
+import org.jetbrains.kotlin.resolve.calls.mpp.AbstractExpectActualCompatibilityChecker
+import org.jetbrains.kotlin.resolve.multiplatform.ExpectActualCompatibility
 import org.jetbrains.kotlin.resolve.multiplatform.OptionalAnnotationUtil
 import org.jetbrains.kotlin.utils.addToStdlib.runIf
+import org.jetbrains.kotlin.utils.addToStdlib.shouldNotBeCalled
 
-private val FLEXIBLE_NULLABILITY_ANNOTATION_FQ_NAME = StandardClassIds.Annotations.FlexibleNullability.asSingleFqName()
+internal fun collectActualCallablesMatchingToSpecificExpect(
+    expectSymbol: IrSymbol,
+    actualSymbols: List<IrSymbol>,
+    expectToActualClassMap: Map<ClassId, IrClassSymbol>,
+    typeSystemContext: IrTypeSystemContext,
+): List<IrSymbol> {
+    val baseExpectSymbol = expectSymbol
+    val matchingActuals = mutableListOf<IrSymbol>()
+    val context = object : IrExpectActualMatchingContext(typeSystemContext, expectToActualClassMap) {
+        override fun onMatchedClasses(expectClassSymbol: IrClassSymbol, actualClassSymbol: IrClassSymbol) {
+            shouldNotBeCalled()
+        }
 
-internal fun Map<String, List<IrDeclaration>>.getMatches(
-    expectDeclaration: IrDeclaration,
-    expectActualTypesMap: Map<IrSymbol, IrSymbol>,
-    expectActualTypeAliasMap: Map<FqName, FqName>
-): List<IrDeclaration> =
-    getMatches(generateIrElementFullNameFromExpect(expectDeclaration, expectActualTypeAliasMap), expectDeclaration, expectActualTypesMap)
-
-internal fun Map<String, List<IrDeclaration>>.getMatches(
-    mainSignature: String,
-    expectDeclaration: IrDeclaration,
-    expectActualTypesMap: Map<IrSymbol, IrSymbol>
-): List<IrDeclaration> {
-    val members = this[mainSignature] ?: return emptyList()
-    return when (expectDeclaration) {
-        is IrFunction -> members.getMatches(expectDeclaration, expectActualTypesMap) { it as IrFunction }
-        is IrProperty -> members.getMatches(expectDeclaration, expectActualTypesMap) { (it as IrProperty).getter!! }
-        else -> members
+        override fun onMatchedCallables(expectSymbol: IrSymbol, actualSymbol: IrSymbol) {
+            require(expectSymbol == baseExpectSymbol)
+            matchingActuals += actualSymbol
+        }
     }
+    AbstractExpectActualCompatibilityChecker.matchSingleExpectTopLevelDeclarationAgainstPotentialActuals(
+        expectSymbol,
+        actualSymbols,
+        context
+    )
+    return matchingActuals
 }
 
-private inline fun List<IrDeclaration>.getMatches(
-    expect: IrDeclaration,
-    expectActualTypesMap: Map<IrSymbol, IrSymbol>,
-    functionExtractor: (IrDeclaration) -> IrFunction
-): List<IrDeclaration> {
-    val expectFunction = functionExtractor(expect)
-    return filter { expectFunction.match(functionExtractor(it), expectActualTypesMap) }
-}
-
-private fun IrFunction.match(actualFunction: IrFunction, expectActualTypesMap: Map<IrSymbol, IrSymbol>): Boolean {
-    fun getActualizedTypeClassifierSymbol(
-        expectParameter: IrValueParameter,
-        localTypeParametersMap: Map<IrTypeParameterSymbol, IrTypeParameterSymbol>? = null
-    ): IrSymbol {
-        return expectParameter.type.classifierOrFail.let {
-            val localMappedSymbol = if (localTypeParametersMap != null && it is IrTypeParameterSymbol) {
-                localTypeParametersMap[it]
-            } else {
-                null
-            }
-            localMappedSymbol ?: expectActualTypesMap[it] ?: it
-        }
-    }
-
-    fun checkParameter(
-        expectParameter: IrValueParameter?,
-        actualParameter: IrValueParameter?,
-        localTypeParametersMap: Map<IrTypeParameterSymbol, IrTypeParameterSymbol>
-    ): Boolean {
-        if (expectParameter == null) {
-            return actualParameter == null
-        }
-        if (actualParameter == null) {
-            return false
-        }
-
-        if (expectParameter.type is IrDynamicType || actualParameter.type is IrDynamicType) {
-            return true
-        }
-
-        if (expectParameter.type.isNullable() != actualParameter.type.isNullable() &&
-            !expectParameter.type.annotations.hasAnnotation(FLEXIBLE_NULLABILITY_ANNOTATION_FQ_NAME) &&
-            !actualParameter.type.annotations.hasAnnotation(FLEXIBLE_NULLABILITY_ANNOTATION_FQ_NAME)
-        ) {
-            return false
-        }
-
-        if (getActualizedTypeClassifierSymbol(expectParameter, localTypeParametersMap) !=
-            getActualizedTypeClassifierSymbol(actualParameter)
-        ) {
-            return false
-        }
-
-        return true
-    }
-
-    if (valueParameters.size != actualFunction.valueParameters.size || typeParameters.size != actualFunction.typeParameters.size) {
-        return false
-    }
-
-    val localTypeParametersMap = mutableMapOf<IrTypeParameterSymbol, IrTypeParameterSymbol>()
-    for ((expectTypeParameter, actualTypeParameter) in typeParameters.zip(actualFunction.typeParameters)) {
-        if (expectTypeParameter.name != actualTypeParameter.name) {
-            return false
-        }
-        localTypeParametersMap[expectTypeParameter.symbol] = actualTypeParameter.symbol
-    }
-
-    if (!checkParameter(extensionReceiverParameter, actualFunction.extensionReceiverParameter, localTypeParametersMap)) {
-        return false
-    }
-
-    for ((expectParameter, actualParameter) in valueParameters.zip(actualFunction.valueParameters)) {
-        if (!checkParameter(expectParameter, actualParameter, localTypeParametersMap)) {
-            return false
-        }
-    }
-
-    return true
-}
-
-internal fun generateActualIrClassOrTypeAliasFullName(declaration: IrElement) = generateIrElementFullNameFromExpect(declaration, emptyMap())
-
-internal fun generateIrElementFullNameFromExpect(
-    declaration: IrElement,
-    expectActualTypeAliasMap: Map<FqName, FqName>
-): String {
-    return buildString { appendElementFullName(declaration, this, expectActualTypeAliasMap) }
-}
-
-private fun appendElementFullName(
-    declaration: IrElement,
-    result: StringBuilder,
-    expectActualTypeAliasMap: Map<FqName, FqName>
+internal fun recordActualForExpectDeclaration(
+    expectSymbol: IrSymbol,
+    actualSymbol: IrSymbol,
+    destination: MutableMap<IrSymbol, IrSymbol>,
 ) {
-    if (declaration !is IrDeclarationBase) return
-
-    val parents = mutableListOf<String>()
-    var parent: IrDeclarationParent? = declaration.parent
-    while (parent != null) {
-        if (parent is IrDeclarationWithName) {
-            val parentParent = parent.parent
-            if (parentParent is IrClass) {
-                parents.add(parent.name.asString())
-                parent = parentParent
-                continue
-            }
+    val expectDeclaration = expectSymbol.owner as IrDeclarationBase
+    val actualDeclaration = actualSymbol.owner as IrDeclaration
+    val registeredActual = destination.put(expectSymbol, actualSymbol)
+    require(registeredActual == null || registeredActual == actualSymbol) {
+        """
+            Expect symbol already has registered mapping
+            
+            Expect declaration: ${expectDeclaration.render()}
+            Actual declaration: ${actualDeclaration.render()}
+            Already registered: ${registeredActual!!.owner.render()}
+        """.trimIndent()
+    }
+    if (expectDeclaration is IrTypeParametersContainer) {
+        recordTypeParametersMapping(destination, expectDeclaration, actualDeclaration as IrTypeParametersContainer)
+    }
+    if (expectDeclaration is IrProperty) {
+        val actualProperty = actualDeclaration as IrProperty
+        expectDeclaration.getter!!.let {
+            val getter = actualProperty.getter!!
+            destination[it.symbol] = getter.symbol
+            recordTypeParametersMapping(destination, it, getter)
         }
-        val parentString = parent.kotlinFqName.let { (expectActualTypeAliasMap[it] ?: it).asString() }
-        if (parentString.isNotEmpty()) {
-            parents.add(parentString)
-        }
-        parent = null
-    }
-
-    if (parents.isNotEmpty()) {
-        result.append(parents.asReversed().joinToString(separator = "."))
-        result.append('.')
-    }
-
-    if (declaration is IrDeclarationWithName) {
-        result.append(declaration.name)
-    }
-
-    if (declaration is IrFunction) {
-        result.append("()")
+        expectDeclaration.setter?.symbol?.let { destination[it] = actualProperty.setter!!.symbol }
     }
 }
 
-internal fun MutableMap<IrSymbol, IrSymbol>.addLink(expectMember: IrDeclarationBase, actualMember: IrDeclaration) {
-    this[expectMember.symbol] = actualMember.symbol
-    if (expectMember is IrProperty) {
-        val actualProperty = actualMember as IrProperty
-        expectMember.getter!!.let {
-            val getter = actualProperty.getter!!
-            this[it.symbol] = getter.symbol
-            this.appendTypeParametersMap(it, getter)
+private fun recordTypeParametersMapping(
+    destination: MutableMap<IrSymbol, IrSymbol>,
+    expectTypeParametersContainer: IrTypeParametersContainer,
+    actualTypeParametersContainer: IrTypeParametersContainer
+) {
+    expectTypeParametersContainer.typeParameters
+        .zip(actualTypeParametersContainer.typeParameters)
+        .forEach { (expectTypeParameter, actualTypeParameter) ->
+            destination[expectTypeParameter.symbol] = actualTypeParameter.symbol
         }
-        expectMember.setter?.symbol?.let { this[it] = actualProperty.setter!!.symbol }
-    } else if (expectMember is IrFunction) {
-        this.appendTypeParametersMap(expectMember, actualMember as IrFunction)
-    }
+}
+
+internal fun KtDiagnosticReporterWithImplicitIrBasedContext.reportMissingActual(expectSymbol: IrSymbol) {
+    reportMissingActual(expectSymbol.owner as IrDeclaration)
 }
 
 @OptIn(ObsoleteDescriptorBasedAPI::class)
@@ -200,6 +107,21 @@ internal fun KtDiagnosticReporterWithImplicitIrBasedContext.reportMissingActual(
     )
 }
 
+internal fun KtDiagnosticReporterWithImplicitIrBasedContext.reportIncompatibleExpectActual(
+    expectSymbol: IrSymbol,
+    actualSymbol: IrSymbol,
+    incompatibility: ExpectActualCompatibility.Incompatible<*>
+) {
+    val expectDeclaration = expectSymbol.owner as IrDeclaration
+    val actualDeclaration = actualSymbol.owner as IrDeclaration
+    at(expectDeclaration).report(
+        CommonBackendErrors.INCOMPATIBLE_MATCHING,
+        expectDeclaration.getNameWithAssert().asString(),
+        actualDeclaration.getNameWithAssert().asString(),
+        incompatibility
+    )
+}
+
 internal fun IrElement.containsOptionalExpectation(): Boolean {
     return this is IrClass &&
             this.kind == ClassKind.ANNOTATION_CLASS &&
@@ -268,4 +190,4 @@ private fun createFakeOverrideFunction(
         it.attributeOwnerId = it
         it.correspondingPropertySymbol = correspondingPropertySymbol
     }
-}
+}

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/IrExpectActualMatchingContext.kt

@@ -0,0 +1,401 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.common.actualizer
+
+import org.jetbrains.kotlin.descriptors.ClassKind
+import org.jetbrains.kotlin.descriptors.Modality
+import org.jetbrains.kotlin.descriptors.Visibilities
+import org.jetbrains.kotlin.descriptors.Visibility
+import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.symbols.*
+import org.jetbrains.kotlin.ir.types.*
+import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
+import org.jetbrains.kotlin.ir.types.impl.IrTypeBase
+import org.jetbrains.kotlin.ir.types.impl.IrTypeProjectionImpl
+import org.jetbrains.kotlin.ir.types.impl.makeTypeProjection
+import org.jetbrains.kotlin.ir.util.*
+import org.jetbrains.kotlin.mpp.*
+import org.jetbrains.kotlin.name.CallableId
+import org.jetbrains.kotlin.name.ClassId
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.resolve.calls.mpp.ExpectActualMatchingContext
+import org.jetbrains.kotlin.types.AbstractTypeChecker
+import org.jetbrains.kotlin.types.Variance
+import org.jetbrains.kotlin.types.model.*
+import org.jetbrains.kotlin.utils.addToStdlib.UnsafeCastFunction
+import org.jetbrains.kotlin.utils.addToStdlib.castAll
+import org.jetbrains.kotlin.utils.addToStdlib.shouldNotBeCalled
+
+internal abstract class IrExpectActualMatchingContext(
+    val typeContext: IrTypeSystemContext,
+    val expectToActualClassMap: Map<ClassId, IrClassSymbol>
+) : ExpectActualMatchingContext<IrSymbol>, TypeSystemContext by typeContext {
+    private inline fun <R> CallableSymbolMarker.processIr(
+        onFunction: (IrFunction) -> R,
+        onProperty: (IrProperty) -> R,
+        onField: (IrField) -> R,
+        onValueParameter: (IrValueParameter) -> R,
+        onEnumEntry: (IrEnumEntry) -> R,
+    ): R {
+        return when (this) {
+            is IrFunctionSymbol -> onFunction(owner)
+            is IrPropertySymbol -> onProperty(owner)
+            is IrFieldSymbol -> onField(owner)
+            is IrValueParameterSymbol -> onValueParameter(owner)
+            is IrEnumEntrySymbol -> onEnumEntry(owner)
+            else -> error("Unsupported declaration: $this")
+        }
+    }
+
+    private inline fun <R> ClassLikeSymbolMarker.processIr(
+        onClass: (IrClass) -> R,
+        onTypeAlias: (IrTypeAlias) -> R,
+    ): R {
+        return when (this) {
+            is IrClassSymbol -> onClass(owner)
+            is IrTypeAliasSymbol -> onTypeAlias(owner)
+            else -> error("Unsupported declaration: $this")
+        }
+    }
+
+    private fun DeclarationSymbolMarker.asIr(): IrDeclaration = (this as IrSymbol).owner as IrDeclaration
+    private fun FunctionSymbolMarker.asIr(): IrFunction = (this as IrFunctionSymbol).owner
+    private fun PropertySymbolMarker.asIr(): IrProperty = (this as IrPropertySymbol).owner
+    private fun ValueParameterSymbolMarker.asIr(): IrValueParameter = (this as IrValueParameterSymbol).owner
+    private fun TypeParameterSymbolMarker.asIr(): IrTypeParameter = (this as IrTypeParameterSymbol).owner
+    private fun RegularClassSymbolMarker.asIr(): IrClass = (this as IrClassSymbol).owner
+    private fun TypeAliasSymbolMarker.asIr(): IrTypeAlias = (this as IrTypeAliasSymbol).owner
+
+    private inline fun <reified T : IrDeclaration> DeclarationSymbolMarker.safeAsIr(): T? = (this as IrSymbol).owner as? T
+
+    override val shouldCheckReturnTypesOfCallables: Boolean
+        get() = true
+
+    override val innerClassesCapturesOuterTypeParameters: Boolean
+        get() = false
+
+    override val RegularClassSymbolMarker.classId: ClassId
+        get() = asIr().classIdOrFail
+
+    override val TypeAliasSymbolMarker.classId: ClassId
+        get() = asIr().classIdOrFail
+
+    override val CallableSymbolMarker.callableId: CallableId
+        get() = processIr(
+            onFunction = { it.callableId },
+            onProperty = { it.callableId },
+            onField = { it.callableId },
+            onValueParameter = { shouldNotBeCalled() },
+            onEnumEntry = { it.callableId }
+        )
+
+    override val TypeParameterSymbolMarker.parameterName: Name
+        get() = asIr().name
+    override val ValueParameterSymbolMarker.parameterName: Name
+        get() = asIr().name
+
+    override fun TypeAliasSymbolMarker.expandToRegularClass(): RegularClassSymbolMarker? {
+        return asIr().expandedType.getClass()?.symbol
+    }
+
+    override val RegularClassSymbolMarker.classKind: ClassKind
+        get() = asIr().kind
+    override val RegularClassSymbolMarker.isCompanion: Boolean
+        get() = asIr().isCompanion
+    override val RegularClassSymbolMarker.isInner: Boolean
+        get() = asIr().isInner
+    override val RegularClassSymbolMarker.isInline: Boolean
+        get() = asIr().isValue
+    override val RegularClassSymbolMarker.isValue: Boolean
+        get() = asIr().isValue
+
+    override val RegularClassSymbolMarker.isFun: Boolean
+        get() = asIr().isFun
+
+    override val ClassLikeSymbolMarker.typeParameters: List<TypeParameterSymbolMarker>
+        get() {
+            val parameters = processIr(
+                onClass = { it.typeParameters },
+                onTypeAlias = { it.typeParameters },
+            )
+            return parameters.map { it.symbol }
+        }
+
+    override val ClassLikeSymbolMarker.modality: Modality
+        get() = processIr(
+            onClass = {
+                // For some reason kotlin annotations in IR have open modality and java annotations have final modality
+                // But since it's legal to actualize kotlin annotation class with java annotation class
+                //  and effectively all annotation classes have the same modality, it's ok to always return one
+                //  modality for all annotation classes (doesn't matter final or open)
+                if (it.isAnnotationClass) Modality.OPEN else it.modality
+            },
+            onTypeAlias = { Modality.FINAL }
+        )
+    override val ClassLikeSymbolMarker.visibility: Visibility
+        get() = safeAsIr<IrDeclarationWithVisibility>()!!.visibility.delegate
+
+    override val CallableSymbolMarker.modality: Modality?
+        get() = when (this) {
+            is IrConstructorSymbol -> Modality.FINAL
+            is IrSymbol -> (owner as? IrOverridableMember)?.modality
+            else -> shouldNotBeCalled()
+        }
+
+    override val CallableSymbolMarker.visibility: Visibility
+        get() = when (this) {
+            is IrEnumEntrySymbol -> Visibilities.Public
+            is IrSymbol -> (owner as IrDeclarationWithVisibility).visibility.delegate
+            else -> shouldNotBeCalled()
+        }
+
+    override val RegularClassSymbolMarker.superTypes: List<KotlinTypeMarker>
+        get() = asIr().superTypes
+
+    override val CallableSymbolMarker.isExpect: Boolean
+        get() = processIr(
+            onFunction = { it.isExpect },
+            onProperty = { it.isExpect },
+            onField = { false },
+            onValueParameter = { false },
+            onEnumEntry = { false }
+        )
+    override val CallableSymbolMarker.isInline: Boolean
+        get() = processIr(
+            onFunction = { it.isInline },
+            onProperty = { false }, // property can not be inline in IR. Its getter is inline instead
+            onField = { false },
+            onValueParameter = { false },
+            onEnumEntry = { false }
+        )
+
+    override val CallableSymbolMarker.isSuspend: Boolean
+        get() = processIr(
+            onFunction = { it.isSuspend },
+            onProperty = { false }, // property can not be suspend in IR. Its getter is suspend instead
+            onField = { false },
+            onValueParameter = { false },
+            onEnumEntry = { false }
+        )
+
+    override val CallableSymbolMarker.isExternal: Boolean
+        get() = safeAsIr<IrPossiblyExternalDeclaration>()?.isExternal ?: false
+
+    override val CallableSymbolMarker.isInfix: Boolean
+        get() = safeAsIr<IrSimpleFunction>()?.isInfix ?: false
+
+    override val CallableSymbolMarker.isOperator: Boolean
+        get() = safeAsIr<IrSimpleFunction>()?.isOperator ?: false
+
+    override val CallableSymbolMarker.isTailrec: Boolean
+        get() = safeAsIr<IrSimpleFunction>()?.isTailrec ?: false
+
+    override val PropertySymbolMarker.isVar: Boolean
+        get() = asIr().isVar
+
+    override val PropertySymbolMarker.isLateinit: Boolean
+        get() = asIr().isLateinit
+
+    override val PropertySymbolMarker.isConst: Boolean
+        get() = asIr().isConst
+
+    override val PropertySymbolMarker.setter: FunctionSymbolMarker?
+        get() = asIr().setter?.symbol
+
+    @OptIn(UnsafeCastFunction::class)
+    override fun createExpectActualTypeParameterSubstitutor(
+        expectTypeParameters: List<TypeParameterSymbolMarker>,
+        actualTypeParameters: List<TypeParameterSymbolMarker>,
+        parentSubstitutor: TypeSubstitutorMarker?,
+    ): TypeSubstitutorMarker {
+        val expectParameters = expectTypeParameters.castAll<IrTypeParameterSymbol>()
+        val actualParameters = actualTypeParameters.castAll<IrTypeParameterSymbol>()
+        val actualTypes = actualParameters.map { it.owner.defaultType }
+        val substitutor = IrTypeSubstitutor(expectParameters, actualTypes, typeContext.irBuiltIns, allowEmptySubstitution = true)
+        return when (parentSubstitutor) {
+            null -> substitutor
+            is AbstractIrTypeSubstitutor -> IrChainedSubstitutor(parentSubstitutor, substitutor)
+            else -> shouldNotBeCalled()
+        }
+    }
+
+    /*
+     * [isActualDeclaration] flag is needed to correctly determine scope for specific class
+     * In IR there are no scopes, all declarations are stored inside IrClass itself, so this flag
+     *   has no sense in IR context
+     */
+    override fun RegularClassSymbolMarker.collectAllMembers(isActualDeclaration: Boolean): List<DeclarationSymbolMarker> {
+        return asIr().declarations.filterNot { it is IrAnonymousInitializer }.map { it.symbol }
+    }
+
+    override fun RegularClassSymbolMarker.getMembersForExpectClass(name: Name): List<DeclarationSymbolMarker> {
+        return asIr().declarations.filter { it.getNameWithAssert() == name }.map { it.symbol }
+    }
+
+    override fun RegularClassSymbolMarker.collectEnumEntryNames(): List<Name> {
+        return asIr().declarations.filterIsInstance<IrEnumEntry>().map { it.name }
+    }
+
+    override val CallableSymbolMarker.dispatchReceiverType: KotlinTypeMarker?
+        get() = (asIr().parent as? IrClass)?.defaultType
+
+    override val CallableSymbolMarker.extensionReceiverType: KotlinTypeMarker?
+        get() = safeAsIr<IrFunction>()?.extensionReceiverParameter?.type
+
+    override val CallableSymbolMarker.returnType: KotlinTypeMarker
+        get() = processIr(
+            onFunction = { it.returnType },
+            onProperty = { it.getter?.returnType ?: it.backingField?.type ?: error("No type for property: $it") },
+            onField = { it.type },
+            onValueParameter = { it.type },
+            onEnumEntry = { it.parentAsClass.defaultType }
+        )
+
+    override val CallableSymbolMarker.typeParameters: List<TypeParameterSymbolMarker>
+        get() = processIr(
+            onFunction = { it.typeParameters.map { parameter -> parameter.symbol } },
+            onProperty = { it.getter?.symbol?.typeParameters.orEmpty() },
+            onField = { emptyList() },
+            onValueParameter = { emptyList() },
+            onEnumEntry = { emptyList() }
+        )
+
+    override val FunctionSymbolMarker.valueParameters: List<ValueParameterSymbolMarker>
+        get() = asIr().valueParameters.map { it.symbol }
+
+    override val ValueParameterSymbolMarker.isVararg: Boolean
+        get() = asIr().isVararg
+    override val ValueParameterSymbolMarker.isNoinline: Boolean
+        get() = asIr().isNoinline
+    override val ValueParameterSymbolMarker.isCrossinline: Boolean
+        get() = asIr().isCrossinline
+    override val ValueParameterSymbolMarker.hasDefaultValue: Boolean
+        get() = asIr().hasDefaultValue()
+
+    override fun CallableSymbolMarker.isAnnotationConstructor(): Boolean {
+        val irConstructor = safeAsIr<IrConstructor>() ?: return false
+        return irConstructor.constructedClass.isAnnotationClass
+    }
+
+    override val TypeParameterSymbolMarker.bounds: List<KotlinTypeMarker>
+        get() = asIr().superTypes
+    override val TypeParameterSymbolMarker.variance: Variance
+        get() = asIr().variance
+    override val TypeParameterSymbolMarker.isReified: Boolean
+        get() = asIr().isReified
+
+    override fun areCompatibleExpectActualTypes(expectType: KotlinTypeMarker?, actualType: KotlinTypeMarker?): Boolean {
+        if (expectType == null) return actualType == null
+        if (actualType == null) return false
+        /*
+         * Here we need to actualize both types, because of following situation:
+         *
+         *   // MODULE: common
+         *   expect fun foo(): S // (1)
+         *   expect class S
+         *
+         *   // MODULE: intermediate
+         *   actual fun foo(): S = null!! // (2)
+         *
+         *   // MODULE: platform
+         *   actual typealias S = String
+         *
+         * When we match return types of (1) and (2) they both will have original type `S`, but from
+         *   perspective of module `platform` it should be replaced with `String`
+         */
+        val actualizedExpectType = actualizingSubstitutor.substitute(expectType as IrType)
+        val actualizedActualType = actualizingSubstitutor.substitute(actualType as IrType)
+        return AbstractTypeChecker.equalTypes(
+            typeContext.newTypeCheckerState(errorTypesEqualToAnything = true, stubTypesEqualToAnything = false),
+            actualizedExpectType,
+            actualizedActualType
+        )
+    }
+
+    private val actualizingSubstitutor = ActualizingSubstitutor()
+
+    private inner class ActualizingSubstitutor : AbstractIrTypeSubstitutor() {
+        override fun substitute(type: IrType): IrType {
+            return substituteOrNull(type) ?: type
+        }
+
+        private fun substituteOrNull(type: IrType): IrType? {
+            if (type !is IrSimpleTypeImpl) return null
+            val newClassifier = (type.classifier.owner as? IrClass)?.let { expectToActualClassMap[it.classIdOrFail] }
+            val newArguments = ArrayList<IrTypeArgument>(type.arguments.size)
+            var argumentsChanged = false
+            for (argument in type.arguments) {
+                val newArgument = substituteArgumentOrNull(argument)
+                if (newArgument != null) {
+                    newArguments += newArgument
+                    argumentsChanged = true
+                } else {
+                    newArguments += argument
+                }
+            }
+            if (newClassifier == null && !argumentsChanged) {
+                return null
+            }
+            return IrSimpleTypeImpl(
+                classifier = newClassifier ?: type.classifier,
+                type.nullability,
+                newArguments,
+                type.annotations,
+                type.abbreviation
+            )
+        }
+
+        private fun substituteArgumentOrNull(argument: IrTypeArgument): IrTypeArgument? {
+            return when (argument) {
+                is IrStarProjection -> null
+                is IrTypeProjection -> when (argument) {
+                    is IrTypeProjectionImpl -> {
+                        val newType = substituteOrNull(argument.type) ?: return null
+                        makeTypeProjection(newType, argument.variance)
+                    }
+                    is IrTypeBase -> substituteOrNull(argument) as IrTypeBase?
+                    else -> shouldNotBeCalled()
+                }
+            }
+        }
+    }
+
+    override fun RegularClassSymbolMarker.isNotSamInterface(): Boolean {
+        // TODO: is it correct for java classes?
+        return !asIr().isFun
+    }
+
+    override fun CallableSymbolMarker.shouldSkipMatching(containingExpectClass: RegularClassSymbolMarker): Boolean {
+        return false
+    }
+
+    override val CallableSymbolMarker.hasStableParameterNames: Boolean
+        get() = when (asIr().origin) {
+            IrDeclarationOrigin.IR_EXTERNAL_DECLARATION_STUB,
+            IrDeclarationOrigin.IR_EXTERNAL_JAVA_DECLARATION_STUB,
+            -> false
+            else -> true
+        }
+
+    override fun onMatchedMembers(expectSymbol: DeclarationSymbolMarker, actualSymbol: DeclarationSymbolMarker) {
+        require(expectSymbol is IrSymbol)
+        require(actualSymbol is IrSymbol)
+        when (expectSymbol) {
+            is IrClassSymbol -> {
+                val actualClassSymbol = when (actualSymbol) {
+                    is IrClassSymbol -> actualSymbol
+                    is IrTypeAliasSymbol -> actualSymbol.owner.expandedType.getClass()!!.symbol
+                    else -> actualSymbol.unexpectedSymbolKind<IrClassifierSymbol>()
+                }
+                onMatchedClasses(expectSymbol, actualClassSymbol)
+            }
+            else -> onMatchedCallables(expectSymbol, actualSymbol)
+        }
+    }
+
+    abstract fun onMatchedClasses(expectClassSymbol: IrClassSymbol, actualClassSymbol: IrClassSymbol)
+    abstract fun onMatchedCallables(expectSymbol: IrSymbol, actualSymbol: IrSymbol)
+}

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrSymbol.kt

@@ -25,6 +25,7 @@ import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrTypeAbbreviation
 import org.jetbrains.kotlin.ir.util.IdSignature
 import org.jetbrains.kotlin.ir.util.SymbolTable
+import org.jetbrains.kotlin.mpp.*
 import org.jetbrains.kotlin.types.model.TypeConstructorMarker
 import org.jetbrains.kotlin.types.model.TypeParameterMarker
 
@@ -46,7 +47,7 @@ import org.jetbrains.kotlin.types.model.TypeParameterMarker
  * @see IdSignature
  * @see SymbolTable
  */
-interface IrSymbol {
+interface IrSymbol : DeclarationSymbolMarker {
 
     /**
      * The declaration that this symbol refers to if it's bound.
@@ -167,7 +168,7 @@ interface IrAnonymousInitializerSymbol : IrBindableSymbol<ClassDescriptor, IrAno
  *
  * @see IrGetEnumValue
  */
-interface IrEnumEntrySymbol : IrBindableSymbol<ClassDescriptor, IrEnumEntry>
+interface IrEnumEntrySymbol : IrBindableSymbol<ClassDescriptor, IrEnumEntry>, EnumEntrySymbolMarker
 
 /**
  * A symbol whose [owner] is [IrField].
@@ -175,7 +176,7 @@ interface IrEnumEntrySymbol : IrBindableSymbol<ClassDescriptor, IrEnumEntry>
  * @see IrGetField
  * @see IrSetField
  */
-interface IrFieldSymbol : IrBindableSymbol<PropertyDescriptor, IrField>
+interface IrFieldSymbol : IrBindableSymbol<PropertyDescriptor, IrField>, FieldSymbolMarker
 
 /**
  * A symbol whose [owner] is [IrClass], [IrScript] or [IrTypeParameter].
@@ -195,7 +196,7 @@ sealed interface IrClassifierSymbol : IrSymbol, TypeConstructorMarker {
  * @see IrCall.superQualifierSymbol
  * @see IrFieldAccessExpression.superQualifierSymbol
  */
-interface IrClassSymbol : IrClassifierSymbol, IrBindableSymbol<ClassDescriptor, IrClass>
+interface IrClassSymbol : IrClassifierSymbol, IrBindableSymbol<ClassDescriptor, IrClass>, RegularClassSymbolMarker
 
 /**
  * A symbol whose [owner] is [IrScript].
@@ -205,7 +206,10 @@ interface IrScriptSymbol : IrClassifierSymbol, IrBindableSymbol<ScriptDescriptor
 /**
  * A symbol whose [owner] is [IrTypeParameter].
  */
-interface IrTypeParameterSymbol : IrClassifierSymbol, IrBindableSymbol<TypeParameterDescriptor, IrTypeParameter>, TypeParameterMarker
+interface IrTypeParameterSymbol : IrClassifierSymbol,
+    IrBindableSymbol<TypeParameterDescriptor, IrTypeParameter>,
+    TypeParameterMarker,
+    TypeParameterSymbolMarker
 
 /**
  * A symbol whose [owner] is [IrValueParameter] or [IrVariable].
@@ -223,7 +227,7 @@ sealed interface IrValueSymbol : IrSymbol {
 /**
  * A symbol whose [owner] is [IrValueParameter].
  */
-interface IrValueParameterSymbol : IrValueSymbol, IrBindableSymbol<ParameterDescriptor, IrValueParameter>
+interface IrValueParameterSymbol : IrValueSymbol, IrBindableSymbol<ParameterDescriptor, IrValueParameter>, ValueParameterSymbolMarker
 
 /**
  * A symbol whose [owner] is [IrVariable].
@@ -247,7 +251,7 @@ sealed interface IrReturnTargetSymbol : IrSymbol {
  *
  * @see IrFunctionReference
  */
-sealed interface IrFunctionSymbol : IrReturnTargetSymbol {
+sealed interface IrFunctionSymbol : IrReturnTargetSymbol, FunctionSymbolMarker {
     override val owner: IrFunction
 }
 
@@ -256,14 +260,14 @@ sealed interface IrFunctionSymbol : IrReturnTargetSymbol {
  *
  * @see IrConstructorCall
  */
-interface IrConstructorSymbol : IrFunctionSymbol, IrBindableSymbol<ClassConstructorDescriptor, IrConstructor>
+interface IrConstructorSymbol : IrFunctionSymbol, IrBindableSymbol<ClassConstructorDescriptor, IrConstructor>, ConstructorSymbolMarker
 
 /**
  * A symbol whose [owner] is [IrSimpleFunction].
  *
  * @see IrCall
  */
-interface IrSimpleFunctionSymbol : IrFunctionSymbol, IrBindableSymbol<FunctionDescriptor, IrSimpleFunction>
+interface IrSimpleFunctionSymbol : IrFunctionSymbol, IrBindableSymbol<FunctionDescriptor, IrSimpleFunction>, SimpleFunctionSymbolMarker
 
 /**
  * A symbol whose [owner] is [IrReturnableBlock].
@@ -273,7 +277,7 @@ interface IrReturnableBlockSymbol : IrReturnTargetSymbol, IrBindableSymbol<Funct
 /**
  * A symbol whose [owner] is [IrProperty].
  */
-interface IrPropertySymbol : IrBindableSymbol<PropertyDescriptor, IrProperty>
+interface IrPropertySymbol : IrBindableSymbol<PropertyDescriptor, IrProperty>, PropertySymbolMarker
 
 /**
  * A symbol whose [owner] is [IrLocalDelegatedProperty].
@@ -285,4 +289,4 @@ interface IrLocalDelegatedPropertySymbol : IrBindableSymbol<VariableDescriptorWi
  *
  * @see IrTypeAbbreviation
  */
-interface IrTypeAliasSymbol : IrBindableSymbol<TypeAliasDescriptor, IrTypeAlias>
+interface IrTypeAliasSymbol : IrBindableSymbol<TypeAliasDescriptor, IrTypeAlias>, TypeAliasSymbolMarker

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSubstitutor.kt

@@ -13,8 +13,11 @@ import org.jetbrains.kotlin.types.Variance
 import org.jetbrains.kotlin.types.model.TypeSubstitutorMarker
 import org.jetbrains.kotlin.utils.memoryOptimizedMap
 
+abstract class AbstractIrTypeSubstitutor : TypeSubstitutorMarker {
+    abstract fun substitute(type: IrType): IrType
+}
 
-abstract class AbstractIrTypeSubstitutor(private val irBuiltIns: IrBuiltIns) : TypeSubstitutorMarker {
+abstract class BaseIrTypeSubstitutor(private val irBuiltIns: IrBuiltIns) : AbstractIrTypeSubstitutor() {
 
     private fun IrType.typeParameterConstructor(): IrTypeParameterSymbol? {
         return if (this is IrSimpleType) classifier as? IrTypeParameterSymbol
@@ -25,7 +28,7 @@ abstract class AbstractIrTypeSubstitutor(private val irBuiltIns: IrBuiltIns) : T
 
     abstract fun isEmptySubstitution(): Boolean
 
-    fun substitute(type: IrType): IrType {
+    final override fun substitute(type: IrType): IrType {
         if (isEmptySubstitution()) return type
         return substituteType(type)
     }
@@ -63,8 +66,9 @@ abstract class AbstractIrTypeSubstitutor(private val irBuiltIns: IrBuiltIns) : T
 class IrTypeSubstitutor(
     typeParameters: List<IrTypeParameterSymbol>,
     typeArguments: List<IrTypeArgument>,
-    irBuiltIns: IrBuiltIns
-) : AbstractIrTypeSubstitutor(irBuiltIns) {
+    irBuiltIns: IrBuiltIns,
+    private val allowEmptySubstitution: Boolean = false
+) : BaseIrTypeSubstitutor(irBuiltIns) {
 
     init {
         assert(typeParameters.size == typeArguments.size) {
@@ -80,7 +84,8 @@ class IrTypeSubstitutor(
 
     override fun getSubstitutionArgument(typeParameter: IrTypeParameterSymbol): IrTypeArgument =
         substitution[typeParameter]
-            ?: throw AssertionError("Unsubstituted type parameter: ${typeParameter.owner.render()}")
+            ?: typeParameter.takeIf { allowEmptySubstitution }?.owner?.defaultType
+            ?: error("Unsubstituted type parameter: ${typeParameter.owner.render()}")
 
     override fun isEmptySubstitution(): Boolean = substitution.isEmpty()
 }
@@ -90,7 +95,7 @@ class IrCapturedTypeSubstitutor(
     typeArguments: List<IrTypeArgument>,
     capturedTypes: List<IrCapturedType?>,
     irBuiltIns: IrBuiltIns
-) : AbstractIrTypeSubstitutor(irBuiltIns) {
+) : BaseIrTypeSubstitutor(irBuiltIns) {
 
     init {
         assert(typeArguments.size == typeParameters.size)
@@ -108,3 +113,10 @@ class IrCapturedTypeSubstitutor(
 
     override fun isEmptySubstitution(): Boolean = oldSubstitution.isEmpty()
 }
+
+class IrChainedSubstitutor(val first: AbstractIrTypeSubstitutor, val second: AbstractIrTypeSubstitutor) : AbstractIrTypeSubstitutor() {
+    override fun substitute(type: IrType): IrType {
+        val firstResult = first.substitute(type)
+        return second.substitute(firstResult)
+    }
+}

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypes.kt

@@ -169,7 +169,7 @@ val IrClassifierSymbol.defaultType: IrType
         is IrScriptSymbol -> unexpectedSymbolKind<IrClassifierSymbol>()
     }
 
-val IrTypeParameter.defaultType: IrType
+val IrTypeParameter.defaultType: IrSimpleType
     get() = IrSimpleTypeImpl(
         symbol,
         SimpleTypeNullability.NOT_SPECIFIED,

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/AdditionalIrUtils.kt

@@ -15,10 +15,7 @@ import org.jetbrains.kotlin.ir.symbols.IrClassifierSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
 import org.jetbrains.kotlin.ir.symbols.impl.IrClassPublicSymbolImpl
-import org.jetbrains.kotlin.name.ClassId
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.name.SpecialNames
+import org.jetbrains.kotlin.name.*
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.utils.filterIsInstanceAnd
 import java.io.File
@@ -57,12 +54,49 @@ val IrDeclarationParent.kotlinFqName: FqName
     }
 
 val IrClass.classId: ClassId?
+    get() = classIdImpl
+
+val IrTypeAlias.classId: ClassId?
+    get() = classIdImpl
+
+private val IrDeclarationWithName.classIdImpl: ClassId?
     get() = when (val parent = this.parent) {
         is IrClass -> parent.classId?.createNestedClassId(this.name)
         is IrPackageFragment -> ClassId.topLevel(parent.packageFqName.child(this.name))
         else -> null
     }
 
+val IrClass.classIdOrFail: ClassId
+    get() = classIdOrFailImpl
+
+val IrTypeAlias.classIdOrFail: ClassId
+    get() = classIdOrFailImpl
+
+private val IrDeclarationWithName.classIdOrFailImpl: ClassId
+    get() = classIdImpl ?: error("No classId for $this")
+
+val IrFunction.callableId: CallableId
+    get() = callableIdImpl
+
+val IrProperty.callableId: CallableId
+    get() = callableIdImpl
+
+val IrField.callableId: CallableId
+    get() = callableIdImpl
+
+val IrEnumEntry.callableId: CallableId
+    get() = callableIdImpl
+
+private val IrDeclarationWithName.callableIdImpl: CallableId
+    get() {
+        if (this.symbol is IrClassifierSymbol) error("Classifiers can not have callableId. Got $this")
+        return when (val parent = this.parent) {
+            is IrClass -> parent.classId?.let { CallableId(it, name) }
+            is IrPackageFragment -> CallableId(parent.packageFqName, name)
+            else -> null
+        } ?: error("$this has no callableId")
+    }
+
 @Suppress("unused")
 @Deprecated(
     "This function is deprecated because it has confusing name and behavior. " +

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt

@@ -802,7 +802,7 @@ open class DeepCopyIrTreeWithSymbols(
             expression.value.transform()
         ).copyAttributes(expression)
 
-    private fun SymbolRemapper.getReferencedReturnTarget(returnTarget: IrReturnTargetSymbol) =
+    private fun SymbolRemapper.getReferencedReturnTarget(returnTarget: IrReturnTargetSymbol): IrReturnTargetSymbol =
         when (returnTarget) {
             is IrFunctionSymbol -> getReferencedFunction(returnTarget)
             is IrReturnableBlockSymbol -> getReferencedReturnableBlock(returnTarget)

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/mpp/AbstractExpectActualCompatibilityChecker.kt

@@ -29,7 +29,7 @@ object AbstractExpectActualCompatibilityChecker {
         context: ExpectActualMatchingContext<T>,
     ): ExpectActualCompatibility<T> {
         val result = with(context) {
-            areCompatibleClassifiers(expectClassSymbol, actualClassLikeSymbol)
+            areCompatibleClassifiers(expectClassSymbol, actualClassLikeSymbol, parentSubstitutor = null)
         }
         @Suppress("UNCHECKED_CAST")
         return result as ExpectActualCompatibility<T>
@@ -50,11 +50,29 @@ object AbstractExpectActualCompatibilityChecker {
         return result as ExpectActualCompatibility<T>
     }
 
+    fun <T : DeclarationSymbolMarker> matchSingleExpectTopLevelDeclarationAgainstPotentialActuals(
+        expectDeclaration: DeclarationSymbolMarker,
+        actualDeclarations: List<DeclarationSymbolMarker>,
+        context: ExpectActualMatchingContext<T>,
+    ) {
+        with(context) {
+            matchSingleExpectAgainstPotentialActuals(
+                expectDeclaration,
+                actualDeclarations,
+                substitutor = null,
+                expectClassSymbol = null,
+                actualClassSymbol = null,
+                unfulfilled = null
+            )
+        }
+    }
+
     context(ExpectActualMatchingContext<*>)
     @Suppress("warnings")
     private fun areCompatibleClassifiers(
         expectClassSymbol: RegularClassSymbolMarker,
         actualClassLikeSymbol: ClassLikeSymbolMarker,
+        parentSubstitutor: TypeSubstitutorMarker?
     ): ExpectActualCompatibility<*> {
         // Can't check FQ names here because nested expected class may be implemented via actual typealias's expansion with the other FQ name
         require(expectClassSymbol.name == actualClassLikeSymbol.name) {
@@ -95,7 +113,7 @@ object AbstractExpectActualCompatibilityChecker {
         val substitutor = createExpectActualTypeParameterSubstitutor(
             expectTypeParameterSymbols,
             actualTypeParameterSymbols,
-            parentSubstitutor = null
+            parentSubstitutor
         )
 
         areCompatibleTypeParameters(expectTypeParameterSymbols, actualTypeParameterSymbols, substitutor).let {
@@ -133,7 +151,7 @@ object AbstractExpectActualCompatibilityChecker {
         actualClassSymbol: RegularClassSymbolMarker,
         substitutor: TypeSubstitutorMarker,
     ): ExpectActualCompatibility<*> {
-        val unfulfilled = arrayListOf<Pair<Any?, Map<Incompatible<Any?>, MutableCollection<Any?>>>>()
+        val unfulfilled = arrayListOf<Pair<DeclarationSymbolMarker, Map<Incompatible<*>, List<DeclarationSymbolMarker?>>>>()
 
         val actualMembersByName = actualClassSymbol.collectAllMembers(isActualDeclaration = true).groupBy { it.name }
 
@@ -145,31 +163,14 @@ object AbstractExpectActualCompatibilityChecker {
                         expectMember is RegularClassSymbolMarker && actualMember is RegularClassSymbolMarker
             }.orEmpty()
 
-            val mapping = actualMembers.keysToMap { actualMember ->
-                when (expectMember) {
-                    is CallableSymbolMarker -> areCompatibleCallables(
-                        expectMember,
-                        actualMember as CallableSymbolMarker,
-                        substitutor,
-                        expectClassSymbol,
-                        actualClassSymbol
-                    )
-
-                    is RegularClassSymbolMarker -> areCompatibleClassifiers(expectMember, actualMember as RegularClassSymbolMarker)
-                    else -> error("Unsupported declaration: $expectMember ($actualMembers)")
-                }
-            }
-            if (mapping.values.any { it == ExpectActualCompatibility.Compatible }) continue
-
-            val incompatibilityMap = mutableMapOf<Incompatible<Any?>, MutableCollection<Any?>>()
-            for ((declaration, compatibility) in mapping) {
-                when (compatibility) {
-                    ExpectActualCompatibility.Compatible -> continue@outer
-                    is Incompatible -> incompatibilityMap.getOrPut(compatibility) { SmartList() }.add(declaration)
-                }
-            }
-
-            unfulfilled.add(expectMember to incompatibilityMap)
+            matchSingleExpectAgainstPotentialActuals(
+                expectMember,
+                actualMembers,
+                substitutor,
+                expectClassSymbol,
+                actualClassSymbol,
+                unfulfilled
+            )
         }
 
         if (expectClassSymbol.classKind == ClassKind.ENUM_CLASS) {
@@ -186,6 +187,53 @@ object AbstractExpectActualCompatibilityChecker {
         return Incompatible.ClassScopes(unfulfilled)
     }
 
+    context(ExpectActualMatchingContext<*>)
+    private fun matchSingleExpectAgainstPotentialActuals(
+        expectMember: DeclarationSymbolMarker,
+        actualMembers: List<DeclarationSymbolMarker>,
+        substitutor: TypeSubstitutorMarker?,
+        expectClassSymbol: RegularClassSymbolMarker?,
+        actualClassSymbol: RegularClassSymbolMarker?,
+        unfulfilled: MutableList<Pair<DeclarationSymbolMarker, Map<Incompatible<*>, List<DeclarationSymbolMarker?>>>>?
+    ) {
+        val mapping = actualMembers.keysToMap { actualMember ->
+            when (expectMember) {
+                is CallableSymbolMarker -> areCompatibleCallables(
+                    expectMember,
+                    actualMember as CallableSymbolMarker,
+                    substitutor,
+                    expectClassSymbol,
+                    actualClassSymbol
+                )
+
+                is RegularClassSymbolMarker -> {
+                    val parentSubstitutor = substitutor?.takeIf { !innerClassesCapturesOuterTypeParameters }
+                    areCompatibleClassifiers(
+                        expectMember,
+                        actualMember as ClassLikeSymbolMarker,
+                        parentSubstitutor
+                    )
+                }
+                else -> error("Unsupported declaration: $expectMember ($actualMembers)")
+            }
+        }
+
+        val incompatibilityMap = mutableMapOf<Incompatible<*>, MutableList<DeclarationSymbolMarker>>()
+        for ((actualMember, compatibility) in mapping) {
+            when (compatibility) {
+                ExpectActualCompatibility.Compatible -> {
+                    onMatchedMembers(expectMember, actualMember)
+                    return
+                }
+
+                is Incompatible -> incompatibilityMap.getOrPut(compatibility) { SmartList() }.add(actualMember)
+            }
+        }
+
+        unfulfilled?.add(expectMember to incompatibilityMap)
+        onMismatchedMembersFromClassScope(expectMember, incompatibilityMap)
+    }
+
     context(ExpectActualMatchingContext<*>)
     private fun areCompatibleCallables(
         expectDeclaration: CallableSymbolMarker,
@@ -307,6 +355,10 @@ object AbstractExpectActualCompatibilityChecker {
                 actualDeclaration
             ).let { if (it != ExpectActualCompatibility.Compatible) return it }
 
+            expectDeclaration is EnumEntrySymbolMarker && actualDeclaration is EnumEntrySymbolMarker -> {
+                // do nothing, entries are matched only by name
+            }
+
             else -> error("Unsupported declarations: $expectDeclaration, $actualDeclaration")
         }
 

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/mpp/ExpectActualMatchingContext.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.mpp.*
 import org.jetbrains.kotlin.name.CallableId
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.resolve.multiplatform.ExpectActualCompatibility
 import org.jetbrains.kotlin.types.Variance
 import org.jetbrains.kotlin.types.model.KotlinTypeMarker
 import org.jetbrains.kotlin.types.model.TypeSubstitutorMarker
@@ -20,6 +21,21 @@ import org.jetbrains.kotlin.types.model.TypeSystemContext
 interface ExpectActualMatchingContext<T : DeclarationSymbolMarker> : TypeSystemContext {
     val shouldCheckReturnTypesOfCallables: Boolean
 
+    /*
+     * This flag indicates how are type parameters of inner classes stored in the specific implementation of RegularClassSymbolMarker
+     *
+     * class Outer<T> {
+     *     inner class Inner<U>
+     * }
+     *
+     * If flag is set to `true` then `typeParameters` for class `Outer.Inner` contains both parameters: [U, R]
+     * Otherwise it contains only parameters of itself: [U]
+     *
+     * This flag is needed for proper calculation of substitutions for components of inner classes
+     */
+    val innerClassesCapturesOuterTypeParameters: Boolean
+        get() = true
+
     val RegularClassSymbolMarker.classId: ClassId
     val TypeAliasSymbolMarker.classId: ClassId
     val CallableSymbolMarker.callableId: CallableId
@@ -100,10 +116,17 @@ interface ExpectActualMatchingContext<T : DeclarationSymbolMarker> : TypeSystemC
     /*
      * Determines should some declaration from expect class scope be checked
      *  - FE 1.0: skip fake overrides
-     *  - FIR: skip nothing
+     *  - FIR: skip fake overrides
      *  - IR: skip nothing
      */
     fun CallableSymbolMarker.shouldSkipMatching(containingExpectClass: RegularClassSymbolMarker): Boolean
 
     val CallableSymbolMarker.hasStableParameterNames: Boolean
+
+    fun onMatchedMembers(expectSymbol: DeclarationSymbolMarker, actualSymbol: DeclarationSymbolMarker) {}
+
+    fun onMismatchedMembersFromClassScope(
+        expectSymbol: DeclarationSymbolMarker,
+        actualSymbolsByIncompatibility: Map<ExpectActualCompatibility.Incompatible<*>, List<DeclarationSymbolMarker>>
+    ) {}
 }

compiler/testData/codegen/box/multiplatform/callToJavaSuper.kt

@@ -1,5 +1,6 @@
 // LANGUAGE: +MultiPlatformProjects
 // WITH_STDLIB
+// FULL_JDK
 // TARGET_BACKEND: JVM_IR
 // IGNORE_BACKEND_K1: JVM_IR
 //   Ignore reason: expect/actual are not supported in K1 box tests

compiler/testData/diagnostics/tests/multiplatform/defaultArguments/methodDefaultArgsViaActualTypealias.fir.kt

@@ -0,0 +1,49 @@
+// !DIAGNOSTICS: -ACTUAL_WITHOUT_EXPECT
+// MODULE: m1-common
+// FILE: common.kt
+expect class A {
+    fun foo(p1: String = "common", p2: String = "common", p3: String)
+}
+
+expect class B {
+    fun foo(s: String)
+}
+
+interface I {
+    fun methodWithDefaultArg(s: String = "common")
+}
+
+expect class WithDefaultArgFromSuper : I {
+    override fun methodWithDefaultArg(s: String)
+}
+
+<!INCOMPATIBLE_MATCHING{JVM}!>expect open class WithIncompatibility {
+    fun foo(p: String = "common")
+}<!>
+
+// MODULE: m2-jvm()()(m1-common)
+// FILE: jvm.kt
+
+class AImpl {
+    fun foo(p1: String = "impl", p2: String = "impl", p3: String) {}
+}
+
+<!DEFAULT_ARGUMENTS_IN_EXPECT_WITH_ACTUAL_TYPEALIAS!>actual typealias A = AImpl<!>
+
+class BImpl {
+    fun foo(s: String = "impl") {}
+}
+
+actual typealias B = BImpl
+
+class WithDefaultArgFromSuperImpl : I {
+    override fun methodWithDefaultArg(s: String) {}
+}
+
+actual typealias WithDefaultArgFromSuper = WithDefaultArgFromSuperImpl
+
+class WithIncompatibilityImpl {
+    fun foo(p: String) {}
+}
+
+<!DEFAULT_ARGUMENTS_IN_EXPECT_WITH_ACTUAL_TYPEALIAS!>actual typealias WithIncompatibility = WithIncompatibilityImpl<!>

compiler/testData/diagnostics/tests/multiplatform/defaultArguments/methodDefaultArgsViaActualTypealias.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // !DIAGNOSTICS: -ACTUAL_WITHOUT_EXPECT
 // MODULE: m1-common
 // FILE: common.kt

compiler/testData/diagnostics/tests/multiplatform/enum/javaEnum.fir.kt

@@ -0,0 +1,34 @@
+// MODULE: m1-common
+// FILE: common.kt
+
+<!INCOMPATIBLE_MATCHING{JVM}, INCOMPATIBLE_MATCHING{JVM}!>expect enum class Foo {
+    ENTRY
+}<!>
+
+expect enum class _TimeUnit
+
+// MODULE: m2-jvm()()(m1-common)
+// FILE: jvm.kt
+
+actual typealias Foo = FooImpl
+
+actual typealias _TimeUnit = java.util.concurrent.TimeUnit
+
+// FILE: FooImpl.java
+
+public enum FooImpl {
+    ENTRY("OK") {
+        @Override
+        public String getResult() {
+            return value;
+        }
+    };
+
+    protected final String value;
+
+    public FooImpl(String value) {
+        this.value = value;
+    }
+
+    public abstract String getResult();
+}

compiler/testData/diagnostics/tests/multiplatform/enum/javaEnum.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // MODULE: m1-common
 // FILE: common.kt
 

compiler/testData/diagnostics/tests/multiplatform/enum/simpleEnum.fir.kt

@@ -0,0 +1,17 @@
+// MODULE: m1-common
+// FILE: common.kt
+
+<!INCOMPATIBLE_MATCHING{JVM}, INCOMPATIBLE_MATCHING{JVM}!>expect enum class Foo {
+    ENTRY1,
+    ENTRY2,
+    ENTRY3;
+}<!>
+
+// MODULE: m2-jvm()()(m1-common)
+// FILE: jvm.kt
+
+actual enum class Foo(val x: String) {
+    ENTRY1("1"),
+    ENTRY2("2"),
+    ENTRY3("3");
+}

compiler/testData/diagnostics/tests/multiplatform/enum/simpleEnum.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // MODULE: m1-common
 // FILE: common.kt
 

compiler/testData/diagnostics/tests/multiplatform/expectInterfaceApplicability.fir.kt

@@ -1,15 +1,15 @@
 // MODULE: m1-common
 // FILE: common.kt
 // TODO: .fir.kt version is just a stub.
-expect interface My {
+<!INCOMPATIBLE_MATCHING{JVM}!>expect interface My {
     open fun openFunPositive()
-    open fun openFunNegative()
+    <!INCOMPATIBLE_MATCHING{JVM}!>open fun openFunNegative()<!>
     abstract fun abstractFun()
 
     open val openValPositive: Int
-    open val openValNegative: Int
+    <!INCOMPATIBLE_MATCHING{JVM}!>open val openValNegative: Int<!>
     abstract val abstractVal: Int
-}
+}<!>
 
 // MODULE: m1-jvm()()(m1-common)
 // FILE: jvm.kt

compiler/testData/diagnostics/tests/multiplatform/generic/typeParameterBoundsDifferentOrderActualMissing.fir.kt

@@ -4,7 +4,7 @@
 interface A
 interface B
 
-expect fun <T> List<T>.foo() where T : A, T : B
+<!INCOMPATIBLE_MATCHING{JVM}!>expect fun <T> List<T>.foo() where T : A, T : B<!>
 
 // MODULE: m2-jvm()()(m1-common)
 // FILE: jvm.kt

compiler/testData/diagnostics/tests/multiplatform/headerClass/actualClassWithDefaultValuesInAnnotationViaTypealias.fir.kt

@@ -7,7 +7,7 @@ expect annotation class Foo3
 expect annotation class Foo4
 expect annotation class Foo5()
 expect annotation class Foo6()
-expect annotation class Foo7()
+<!INCOMPATIBLE_MATCHING{JVM}!>expect annotation class Foo7<!INCOMPATIBLE_MATCHING{JVM}!>()<!><!>
 
 @<!UNRESOLVED_REFERENCE!>Foo1<!>
 fun foo() {}

compiler/testData/diagnostics/tests/multiplatform/headerClass/actualClassWithDifferentConstructors.fir.kt

@@ -5,9 +5,9 @@ expect class Foo1
 expect class Foo2
 expect class Foo3
 
-expect class Bar1()
-expect class Bar2()
-expect class Bar3()
+<!INCOMPATIBLE_MATCHING{JVM}!>expect class Bar1<!INCOMPATIBLE_MATCHING{JVM}!>()<!><!>
+<!INCOMPATIBLE_MATCHING{JVM}!>expect class Bar2<!INCOMPATIBLE_MATCHING{JVM}!>()<!><!>
+<!INCOMPATIBLE_MATCHING{JVM}!>expect class Bar3<!INCOMPATIBLE_MATCHING{JVM}!>()<!><!>
 expect class Bar4()
 expect class Bar5()
 expect class Bar6()

compiler/testData/diagnostics/tests/multiplatform/headerClass/expectDeclarationWithStrongIncompatibilities.fir.kt

@@ -3,12 +3,12 @@
 // FILE: common.kt
 
 expect fun foo1(x: Int)
-<!NO_ACTUAL_FOR_EXPECT{JVM}!>expect fun foo2(x: Int)<!>
+<!INCOMPATIBLE_MATCHING{JVM}, INCOMPATIBLE_MATCHING{JVM}!>expect fun foo2(x: Int)<!>
 
 expect class NoArgConstructor()
 
-expect fun foo3(): Int
-<!NO_ACTUAL_FOR_EXPECT{JVM}!>expect fun foo4(): Int<!>
+<!INCOMPATIBLE_MATCHING{JVM}!>expect fun foo3(): Int<!>
+<!INCOMPATIBLE_MATCHING{JVM}!>expect fun foo4(): Int<!>
 
 // MODULE: m2-jvm()()(m1-common)
 

compiler/testData/diagnostics/tests/multiplatform/headerClass/expectFunInterface.fir.kt

@@ -5,9 +5,9 @@ expect fun interface F1 {
     fun run()
 }
 
-expect fun interface F2 {
+<!INCOMPATIBLE_MATCHING{JVM}!>expect fun interface F2 {
     fun run()
-}
+}<!>
 
 expect fun interface F3 {
     fun run()
@@ -21,9 +21,9 @@ expect fun interface F5 {
     fun run()
 }
 
-expect fun interface F6 {
+<!INCOMPATIBLE_MATCHING{JVM}!>expect fun interface F6 {
     fun run()
-}
+}<!>
 
 // MODULE: m2-jvm()()(m1-common)
 

compiler/testData/diagnostics/tests/multiplatform/headerClass/genericClassImplTypeAlias.fir.kt

@@ -0,0 +1,37 @@
+// !DIAGNOSTICS: -ACTUAL_WITHOUT_EXPECT
+// MODULE: m1-common
+// FILE: common.kt
+
+expect class C1
+<!INCOMPATIBLE_MATCHING{JVM}!>expect interface C2<A><!>
+<!INCOMPATIBLE_MATCHING{JVM}!>expect interface C3<B><!>
+expect interface C4<D, E>
+expect interface C5<F, G>
+expect interface C6<H>
+expect interface C7<I>
+expect interface C8<J>
+expect interface C9<K>
+expect interface C10<L>
+
+// MODULE: m2-jvm()()(m1-common)
+// FILE: jvm.kt
+
+class A<T : A<T>>
+class B<T>
+
+actual typealias C1 = String
+<!ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE!>actual typealias C2<A> = List<String><!>
+<!ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE!>actual typealias C3<B> = List<B><!>
+actual typealias C4<D, E> = MutableMap<D, E>
+<!ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION!>actual typealias C5<F, G> = MutableMap<G, F><!>
+<!ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION!>actual typealias C51 = MutableMap<String, String><!>
+<!ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION!>actual typealias C52<F> = MutableMap<F, String><!>
+<!ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION!>actual typealias C53<T> = A<A<T>><!>
+<!ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION!>actual typealias C54<T> = B<List<String>><!>
+actual typealias C6<H> = MutableList<H>
+<!ACTUAL_TYPE_ALIAS_WITH_USE_SITE_VARIANCE!>actual typealias C7<I> = MutableList<out I><!>
+<!ACTUAL_TYPE_ALIAS_WITH_USE_SITE_VARIANCE!>actual typealias C8<J> = MutableList<*><!>
+<!ACTUAL_TYPE_ALIAS_WITH_USE_SITE_VARIANCE!>actual typealias C9<K> = MutableList<in K><!>
+
+typealias Tmp<K> = MutableList<K>
+<!ACTUAL_TYPE_ALIAS_NOT_TO_CLASS!>actual typealias C10<L> = Tmp<L><!>

compiler/testData/diagnostics/tests/multiplatform/headerClass/genericClassImplTypeAlias.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // !DIAGNOSTICS: -ACTUAL_WITHOUT_EXPECT
 // MODULE: m1-common
 // FILE: common.kt

compiler/testData/diagnostics/tests/multiplatform/headerClass/morePermissiveVisibilityOnActual.fir.kt

@@ -2,20 +2,20 @@
 // MODULE: m1-common
 // FILE: common.kt
 
-expect open class Container {
+<!INCOMPATIBLE_MATCHING{JVM}!>expect open class Container {
     fun publicFun()
 
     internal fun internalFun1()
     internal fun internalFun2()
-    internal fun internalFun3()
+    <!INCOMPATIBLE_MATCHING{JVM}!>internal fun internalFun3()<!>
 
     protected fun protectedFun1()
     protected fun protectedFun2()
-    protected fun protectedFun3()
+    <!INCOMPATIBLE_MATCHING{JVM}!>protected fun protectedFun3()<!>
 
-    open internal fun openInternalFun()
-    open fun openPublicFun()
-}
+    <!INCOMPATIBLE_MATCHING{JVM}!>open internal fun openInternalFun()<!>
+    <!INCOMPATIBLE_MATCHING{JVM}!>open fun openPublicFun()<!>
+}<!>
 
 // MODULE: m2-jvm()()(m1-common)
 

compiler/testData/diagnostics/tests/multiplatform/headerClass/nestedClassesWithErrors.fir.kt

@@ -14,9 +14,9 @@ expect class C {
     <!WRONG_MODIFIER_TARGET!>expect<!> inner class I
 }
 
-expect class D {
+<!INCOMPATIBLE_MATCHING{JVM}!>expect class D {
     <!NO_ACTUAL_FOR_EXPECT{JVM}!>class N<!>
-}
+}<!>
 
 expect class E {
     class N

compiler/testData/diagnostics/tests/multiplatform/headerClass/noImplKeywordOnMember.fir.kt

@@ -1,10 +1,10 @@
 // MODULE: m1-common
 // FILE: common.kt
 
-expect class Foo {
+<!INCOMPATIBLE_MATCHING{JVM}!>expect class Foo {
     fun bar(): String
-    fun bas(f: Int)
-}
+    <!INCOMPATIBLE_MATCHING{JVM}!>fun bas(f: Int)<!>
+}<!>
 
 // MODULE: m2-jvm()()(m1-common)
 // FILE: jvm.kt

compiler/testData/diagnostics/tests/multiplatform/headerClass/superClass.fir.kt

@@ -7,7 +7,7 @@ interface J
 
 expect class Foo : I, C, J
 
-<!SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR, SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR!>expect class Bar : C()<!>
+<!INCOMPATIBLE_MATCHING{JVM}, SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR, SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR!>expect class Bar : C()<!>
 
 // MODULE: m2-jvm()()(m1-common)
 // FILE: jvm.kt

compiler/testData/diagnostics/tests/multiplatform/headerFunInNonHeaderClass.fir.kt

@@ -2,7 +2,7 @@
 // FILE: common.kt
 
 class Foo {
-    <!NON_ABSTRACT_FUNCTION_WITH_NO_BODY, NO_ACTUAL_FOR_EXPECT{JVM}!><!WRONG_MODIFIER_TARGET!>expect<!> fun bar(): String<!>
+    <!NON_ABSTRACT_FUNCTION_WITH_NO_BODY!><!WRONG_MODIFIER_TARGET!>expect<!> fun bar(): String<!>
 }
 
 // MODULE: m1-jvm()()(m1-common)

compiler/testData/diagnostics/tests/multiplatform/hmpp/kt57320.fir.kt

@@ -26,7 +26,7 @@ interface KotlinXStringDemoInterface {
     val value: String
 }
 
-expect fun StringDemoInterface.plusK(): String
+<!INCOMPATIBLE_MATCHING{JS}!>expect fun StringDemoInterface.plusK(): String<!>
 
 // MODULE: js()()(common, intermediate)
 // TARGET_PLATFORM: JS
@@ -34,7 +34,7 @@ expect fun StringDemoInterface.plusK(): String
 // FILE: StringDemoInterface.kt
 actual typealias StringDemoInterface = KotlinXStringDemoInterface
 
-<!ACTUAL_WITHOUT_EXPECT("actual  fun StringDemoInterface.plusK(): <ERROR TYPE REF: Unresolved name: value>; The following declaration is incompatible:    expect fun StringDemoInterface.plusK(): String")!>actual fun StringDemoInterface.plusK() = <!RESOLUTION_TO_CLASSIFIER!>StringValue<!>(value).plus("K").<!UNRESOLVED_REFERENCE!>value<!><!>
+<!ACTUAL_WITHOUT_EXPECT("actual  fun StringDemoInterface.plusK(): <ERROR TYPE REF: Unresolved name: value>; The following declaration is incompatible:    expect fun StringDemoInterface.plusK(): String")!>actual fun StringDemoIn<!INCOMPATIBLE_MATCHING!>terface.plusK() = <!RESOLUTION_TO_CLASSIFIER!>StringValue<!>(value).plus("K")<!>.<!UNRESOLVED_REFERENCE!>value<!><!>
 
 // FILE: main.kt
 class StringDemo(override val value: String) : StringDemoInterface

compiler/testData/diagnostics/tests/multiplatform/hmpp/multiplatformCompositeAnalysis/expectAndActualInTheSameModule.fir.kt

@@ -3,10 +3,10 @@
 // TARGET_PLATFORM: Common
 
 <!NO_ACTUAL_FOR_EXPECT{JVM}!>expect class CommonClass {
-    <!NO_ACTUAL_FOR_EXPECT{JVM}!>fun memberFun()<!>
-    <!NO_ACTUAL_FOR_EXPECT{JVM}!>val memberProp: Int<!>
-    <!NO_ACTUAL_FOR_EXPECT{JVM}!>class Nested<!>
-    <!NO_ACTUAL_FOR_EXPECT{JVM}!>inner class Inner<!>
+    fun memberFun()
+    val memberProp: Int
+    class Nested
+    inner class Inner
 }<!>
 <!ACTUAL_WITHOUT_EXPECT!>actual class CommonClass {
     <!ACTUAL_WITHOUT_EXPECT!>actual fun memberFun() {}<!>

compiler/testData/diagnostics/tests/multiplatform/hmpp/multiplatformCompositeAnalysis/expectAndActualInTheSameModuleIncompatibilities.fir.kt

@@ -13,8 +13,8 @@ val callableKind: Int = 1
 expect fun <T> typeParameterCount()
 fun typeParameterCount() {}
 
-<!NO_ACTUAL_FOR_EXPECT{JVM}, NO_ACTUAL_FOR_EXPECT{JVM}, NO_ACTUAL_FOR_EXPECT{JVM}, NO_ACTUAL_FOR_EXPECT{JVM}!>expect enum class EnumEntries {
-    <!NO_ACTUAL_FOR_EXPECT{JVM}!>ONE,<!> <!NO_ACTUAL_FOR_EXPECT{JVM}!>TWO;<!>
+<!NO_ACTUAL_FOR_EXPECT{JVM}!>expect enum class EnumEntries {
+    ONE, TWO;
 }<!>
 <!ACTUAL_WITHOUT_EXPECT!>actual enum class EnumEntries {
     ONE;

compiler/testData/diagnostics/tests/multiplatform/java/flexibleTypes.fir.kt

@@ -1,31 +0,0 @@
-// MODULE: m1-common
-// FILE: common.kt
-
-expect class Foo {
-    constructor(p: Any)
-
-    fun f1(s: String): Int
-
-    <!NO_ACTUAL_FOR_EXPECT{JVM}!>fun f2(s: List<String>?): MutableMap<Boolean?, Foo><!>
-
-    fun <T : Set<Number>> f3(t: T): T?
-}
-
-// MODULE: m2-jvm()()(m1-common)
-// FILE: FooImpl.java
-
-import java.util.*;
-
-public class FooImpl {
-    public FooImpl(Object p) {}
-
-    public final int f1(String s) { return 0; }
-
-    public final Map<Boolean, FooImpl> f2(List<String> s) { return null; }
-
-    public final <T extends Set<Number>> T f3(T t) { return null; }
-}
-
-// FILE: jvm.kt
-
-actual typealias Foo = FooImpl

compiler/testData/diagnostics/tests/multiplatform/java/flexibleTypes.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // MODULE: m1-common
 // FILE: common.kt
 

compiler/testData/diagnostics/tests/multiplatform/kt54827.fir.kt

@@ -1,8 +1,8 @@
 // MODULE: m1-common
 // FILE: common.kt
-expect class SomeClass<T> {
+<!INCOMPATIBLE_MATCHING{JVM}!>expect class SomeClass<T> {
     fun foo()
-}
+}<!>
 
 // MODULE: m1-jvm()()(m1-common)
 // FILE: jvm.kt

compiler/testData/diagnostics/tests/multiplatform/topLevelFun/inlineFun.fir.kt

@@ -1,7 +1,7 @@
 // MODULE: m1-common
 // FILE: common.kt
 
-inline expect fun inlineFun()
+<!INCOMPATIBLE_MATCHING{JVM}!>inline expect fun inlineFun()<!>
 expect fun nonInlineFun()
 
 // MODULE: m2-jvm()()(m1-common)

compiler/testData/diagnostics/tests/multiplatform/topLevelFun/valueParameterModifiers.fir.kt

@@ -3,15 +3,15 @@
 // FILE: common.kt
 
 expect fun f1(s: () -> String)
-expect inline fun f2(s: () -> String)
+<!INCOMPATIBLE_MATCHING{JVM}!>expect inline fun f2(s: () -> String)<!>
 expect inline fun f3(noinline s: () -> String)
 
 expect fun f4(s: () -> String)
-expect inline fun f5(s: () -> String)
+<!INCOMPATIBLE_MATCHING{JVM}!>expect inline fun f5(s: () -> String)<!>
 expect inline fun f6(crossinline s: () -> String)
 
-<!NO_ACTUAL_FOR_EXPECT{JVM}!>expect fun f7(x: Any)<!>
-<!NO_ACTUAL_FOR_EXPECT{JVM}!>expect fun f8(vararg x: Any)<!>
+<!INCOMPATIBLE_MATCHING{JVM}!>expect fun f7(x: Any)<!>
+<!INCOMPATIBLE_MATCHING{JVM}!>expect fun f8(vararg x: Any)<!>
 
 // MODULE: m2-jvm()()(m1-common)
 // FILE: jvm.kt

compiler/testData/diagnostics/tests/multiplatform/varSetterVisibility.fir.kt

@@ -1,20 +1,20 @@
 // MODULE: m1-common
 // FILE: common.kt
-expect var v1: Boolean
+<!INCOMPATIBLE_MATCHING{JVM}!>expect var v1: Boolean<!>
 
 expect var v2: Boolean
     internal set
 
-expect var v3: Boolean
-    internal set
+<!INCOMPATIBLE_MATCHING{JVM}!>expect var v3: Boolean
+    internal set<!>
 
-expect open class C {
-    var foo: Boolean
-}
+<!INCOMPATIBLE_MATCHING{JVM}!>expect open class C {
+    <!INCOMPATIBLE_MATCHING{JVM}!>var foo: Boolean<!>
+}<!>
 
-expect open class C2 {
-    var foo: Boolean
-}
+<!INCOMPATIBLE_MATCHING{JVM}!>expect open class C2 {
+    <!INCOMPATIBLE_MATCHING{JVM}!>var foo: Boolean<!>
+}<!>
 
 // MODULE: m1-jvm()()(m1-common)
 // FILE: jvm.kt

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/backend/ir/ActualizerOnlyFacade.kt

@@ -6,8 +6,11 @@
 package org.jetbrains.kotlin.test.backend.ir
 
 import org.jetbrains.kotlin.backend.common.actualizer.IrActualizer
+import org.jetbrains.kotlin.backend.jvm.JvmIrTypeSystemContext
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.config.languageVersionSettings
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContextImpl
+import org.jetbrains.kotlin.platform.jvm.isJvm
 import org.jetbrains.kotlin.test.model.*
 import org.jetbrains.kotlin.test.services.TestServices
 import org.jetbrains.kotlin.test.services.compilerConfigurationProvider
@@ -17,10 +20,16 @@ class ActualizerOnlyFacade(
 ) : AbstractTestFacade<IrBackendInput, IrBackendInput>() {
     override fun transform(module: TestModule, inputArtifact: IrBackendInput): IrBackendInput {
         if (module.useIrActualizer()) {
+            val builtins = inputArtifact.irModuleFragment.irBuiltins
+            val typeSystemContext = when (module.targetPlatform.isJvm()) {
+                true -> JvmIrTypeSystemContext(builtins)
+                false -> IrTypeSystemContextImpl(builtins)
+            }
             IrActualizer.actualize(
                 inputArtifact.irModuleFragment,
                 inputArtifact.dependentIrModuleFragments,
                 inputArtifact.diagnosticReporter,
+                typeSystemContext,
                 testServices.compilerConfigurationProvider.getCompilerConfiguration(module).languageVersionSettings
             )
         }
@@ -35,4 +44,4 @@ class ActualizerOnlyFacade(
     override val outputKind: TestArtifactKind<IrBackendInput> = BackendKinds.IrBackend
 
     override fun shouldRunAnalysis(module: TestModule): Boolean = true
-}
+}

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/backend/ir/JvmIrBackendFacade.kt

@@ -8,12 +8,14 @@ package org.jetbrains.kotlin.test.backend.ir
 import org.jetbrains.kotlin.KtPsiSourceFile
 import org.jetbrains.kotlin.backend.common.BackendException
 import org.jetbrains.kotlin.backend.common.actualizer.IrActualizer
+import org.jetbrains.kotlin.backend.jvm.JvmIrTypeSystemContext
 import org.jetbrains.kotlin.backend.jvm.MultifileFacadeFileEntry
 import org.jetbrains.kotlin.backend.jvm.lower.getFileClassInfoFromIrFile
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.fileClasses.JvmFileClassUtil
 import org.jetbrains.kotlin.ir.PsiIrFileEntry
 import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContextImpl
 import org.jetbrains.kotlin.ir.util.NaiveSourceBasedFileEntryImpl
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.test.backend.classic.JavaCompilerFacade
@@ -40,6 +42,7 @@ class JvmIrBackendFacade(
                 inputArtifact.irModuleFragment,
                 inputArtifact.dependentIrModuleFragments,
                 inputArtifact.state.diagnosticReporter,
+                JvmIrTypeSystemContext(inputArtifact.irModuleFragment.irBuiltins),
                 inputArtifact.state.languageVersionSettings
             )
         }

core/compiler.common/src/org/jetbrains/kotlin/mpp/DeclarationSymbolMarkers.kt

@@ -17,6 +17,8 @@ interface ConstructorSymbolMarker : FunctionSymbolMarker
 interface SimpleFunctionSymbolMarker : FunctionSymbolMarker
 interface PropertySymbolMarker : CallableSymbolMarker
 interface ValueParameterSymbolMarker : CallableSymbolMarker
+interface FieldSymbolMarker : CallableSymbolMarker
+interface EnumEntrySymbolMarker : CallableSymbolMarker
 
 interface ClassifierSymbolMarker : DeclarationSymbolMarker
 interface TypeParameterSymbolMarker : ClassifierSymbolMarker

core/compiler.common/src/org/jetbrains/kotlin/resolve/multiplatform/ExpectActualCompatibility.kt

@@ -5,6 +5,9 @@
 
 package org.jetbrains.kotlin.resolve.multiplatform
 
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
 sealed class ExpectActualCompatibility<out D> {
     // For IncompatibilityKind.STRONG `actual` declaration is considered as overload and error reports on expected declaration
     enum class IncompatibilityKind {
@@ -95,3 +98,11 @@ sealed class ExpectActualCompatibility<out D> {
 
 val ExpectActualCompatibility<*>.compatible: Boolean
     get() = this == ExpectActualCompatibility.Compatible
+
+@OptIn(ExperimentalContracts::class)
+fun ExpectActualCompatibility<*>.isIncompatible(): Boolean {
+    contract {
+        returns(true) implies (this@isIncompatible is ExpectActualCompatibility.Incompatible<*>)
+    }
+    return !compatible
+}

js/js.tests/test/org/jetbrains/kotlin/js/test/converters/FirJsKlibBackendFacade.kt

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.incremental.components.LookupTracker
 import org.jetbrains.kotlin.ir.backend.js.JsFactories
 import org.jetbrains.kotlin.ir.backend.js.resolverLogger
 import org.jetbrains.kotlin.ir.backend.js.serializeModuleIntoKlib
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContextImpl
 import org.jetbrains.kotlin.ir.util.IrMessageLogger
 import org.jetbrains.kotlin.js.test.utils.JsIrIncrementalDataProvider
 import org.jetbrains.kotlin.js.test.utils.jsIrIncrementalDataProvider
@@ -71,6 +72,7 @@ class FirJsKlibBackendFacade(
                         inputArtifact.irModuleFragment,
                         inputArtifact.dependentIrModuleFragments,
                         diagnosticReporter,
+                        IrTypeSystemContextImpl(inputArtifact.irModuleFragment.irBuiltins),
                         configuration.languageVersionSettings
                     )
                 } else {
@@ -124,4 +126,4 @@ class FirJsKlibBackendFacade(
 
         return BinaryArtifacts.KLib(File(outputFile))
     }
-}
+}

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/Fir2Ir.kt

@@ -31,6 +31,7 @@ import org.jetbrains.kotlin.fir.signaturer.Ir2FirManglerAdapter
 import org.jetbrains.kotlin.incremental.components.LookupTracker
 import org.jetbrains.kotlin.ir.declarations.IrDeclaration
 import org.jetbrains.kotlin.ir.declarations.IrExternalPackageFragment
+import org.jetbrains.kotlin.ir.types.IrTypeSystemContextImpl
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
 import org.jetbrains.kotlin.library.metadata.KlibMetadataFactories
@@ -87,6 +88,7 @@ internal fun PhaseContext.fir2Ir(
             visibilityConverter = Fir2IrVisibilityConverter.Default,
             diagnosticReporter = diagnosticsReporter,
             kotlinBuiltIns = builtInsModule ?: DefaultBuiltIns.Instance,
+            actualizerTypeContextProvider = ::IrTypeSystemContextImpl,
             fir2IrResultPostCompute = {
                 // it's important to compare manglers before actualization, since IR will be actualized, while FIR won't
                 irModuleFragment.acceptVoid(