IR: make subtypes of IrDeclaration classes

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyClass.kt

@@ -31,7 +31,7 @@ class Fir2IrLazyClass(
     override var origin: IrDeclarationOrigin,
     override val fir: FirRegularClass,
     override val symbol: Fir2IrClassSymbol,
-) : IrClass, AbstractFir2IrLazyDeclaration<FirRegularClass, IrClass>, Fir2IrComponents by components {
+) : IrClass(), AbstractFir2IrLazyDeclaration<FirRegularClass, IrClass>, Fir2IrComponents by components {
     init {
         symbol.bind(this)
         classifierStorage.preCacheTypeParameters(fir)

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyConstructor.kt

@@ -29,7 +29,7 @@ class Fir2IrLazyConstructor(
     override var origin: IrDeclarationOrigin,
     override val fir: FirConstructor,
     override val symbol: Fir2IrConstructorSymbol,
-) : IrConstructor, AbstractFir2IrLazyDeclaration<FirConstructor, IrConstructor>, Fir2IrComponents by components {
+) : IrConstructor(), AbstractFir2IrLazyDeclaration<FirConstructor, IrConstructor>, Fir2IrComponents by components {
     init {
         symbol.bind(this)
         classifierStorage.preCacheTypeParameters(fir)

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyProperty.kt

@@ -32,7 +32,7 @@ class Fir2IrLazyProperty(
     override val fir: FirProperty,
     override val symbol: Fir2IrPropertySymbol,
     override val isFakeOverride: Boolean
-) : IrProperty, AbstractFir2IrLazyDeclaration<FirProperty, IrProperty>, Fir2IrComponents by components {
+) : IrProperty(), AbstractFir2IrLazyDeclaration<FirProperty, IrProperty>, Fir2IrComponents by components {
     init {
         symbol.bind(this)
         classifierStorage.preCacheTypeParameters(fir)

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazySimpleFunction.kt

@@ -33,7 +33,7 @@ class Fir2IrLazySimpleFunction(
     firParent: FirRegularClass,
     override val symbol: Fir2IrSimpleFunctionSymbol,
     override val isFakeOverride: Boolean
-) : IrSimpleFunction, AbstractFir2IrLazyDeclaration<FirSimpleFunction, IrSimpleFunction>, Fir2IrComponents by components {
+) : IrSimpleFunction(), AbstractFir2IrLazyDeclaration<FirSimpleFunction, IrSimpleFunction>, Fir2IrComponents by components {
     init {
         symbol.bind(this)
         classifierStorage.preCacheTypeParameters(fir)

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrAnonymousInitializerImpl.kt

@@ -32,7 +32,7 @@ class IrAnonymousInitializerImpl(
     override var origin: IrDeclarationOrigin,
     override val symbol: IrAnonymousInitializerSymbol,
     override val isStatic: Boolean = false
-) : IrAnonymousInitializer {
+) : IrAnonymousInitializer() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt

@@ -41,7 +41,7 @@ class IrClassImpl(
     override val isExpect: Boolean = false,
     override val isFun: Boolean = false,
     override val source: SourceElement = SourceElement.NO_SOURCE
-) : IrClass {
+) : IrClass() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrConstructorImpl.kt

@@ -38,7 +38,7 @@ class IrConstructorImpl(
     override val isExternal: Boolean,
     override val isPrimary: Boolean,
     override val isExpect: Boolean,
-) : IrConstructor {
+) : IrConstructor() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrEnumEntryImpl.kt

@@ -30,7 +30,7 @@ class IrEnumEntryImpl(
     override var origin: IrDeclarationOrigin,
     override val symbol: IrEnumEntrySymbol,
     override val name: Name
-) : IrEnumEntry {
+) : IrEnumEntry() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrErrorDeclarationImpl.kt

@@ -29,7 +29,7 @@ class IrErrorDeclarationImpl(
     override val startOffset: Int,
     override val endOffset: Int,
     override val descriptor: DeclarationDescriptor
-) : IrErrorDeclaration {
+) : IrErrorDeclaration() {
     override var origin: IrDeclarationOrigin = IrDeclarationOrigin.DEFINED
 
     override val factory: IrFactory

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt

@@ -38,7 +38,7 @@ class IrFieldImpl(
     override val isFinal: Boolean,
     override val isExternal: Boolean,
     override val isStatic: Boolean,
-) : IrField {
+) : IrField() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrFunctionImpl.kt

@@ -32,7 +32,7 @@ abstract class IrFunctionCommonImpl(
     override val isOperator: Boolean,
     override val isInfix: Boolean,
     override val isExpect: Boolean,
-) : IrSimpleFunction {
+) : IrSimpleFunction() {
     override val factory: IrFactory
         get() = IrFactoryImpl
 

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrLocalDelegatedPropertyImpl.kt

@@ -32,7 +32,7 @@ class IrLocalDelegatedPropertyImpl(
     override val name: Name,
     override val type: IrType,
     override val isVar: Boolean
-) : IrLocalDelegatedProperty {
+) : IrLocalDelegatedProperty() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt

@@ -38,7 +38,7 @@ abstract class IrPropertyCommonImpl(
     override val isDelegated: Boolean,
     override val isExternal: Boolean,
     override val isExpect: Boolean,
-) : IrProperty {
+) : IrProperty() {
     override val factory: IrFactory
         get() = IrFactoryImpl
 

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt

@@ -23,7 +23,7 @@ class IrTypeAliasImpl(
     override val expandedType: IrType,
     override val isActual: Boolean,
     override var origin: IrDeclarationOrigin
-) : IrTypeAlias {
+) : IrTypeAlias() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeParameterImpl.kt

@@ -38,7 +38,7 @@ class IrTypeParameterImpl(
     override val index: Int,
     override val isReified: Boolean,
     override val variance: Variance
-) : IrTypeParameter {
+) : IrTypeParameter() {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrValueParameterImpl.kt

@@ -39,7 +39,7 @@ class IrValueParameterImpl(
     override val varargElementType: IrType?,
     override val isCrossinline: Boolean,
     override val isNoinline: Boolean
-) : IrValueParameter {
+) : IrValueParameter() {
     @ObsoleteDescriptorBasedAPI
     override val descriptor: ParameterDescriptor
         get() = symbol.descriptor

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrAnonymousInitializer.kt

@@ -34,8 +34,8 @@ internal class PersistentIrAnonymousInitializer(
     origin: IrDeclarationOrigin,
     override val symbol: IrAnonymousInitializerSymbol,
     override val isStatic: Boolean = false
-) : PersistentIrDeclarationBase<AnonymousInitializerCarrier>,
+) : IrAnonymousInitializer(),
-    IrAnonymousInitializer,
+    PersistentIrDeclarationBase<AnonymousInitializerCarrier>,
     AnonymousInitializerCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrClass.kt

@@ -44,9 +44,8 @@ internal class PersistentIrClass(
     override val isExpect: Boolean = false,
     override val isFun: Boolean = false,
     override val source: SourceElement = SourceElement.NO_SOURCE
-) :
+) : IrClass(),
     PersistentIrDeclarationBase<ClassCarrier>,
-    IrClass,
     ClassCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrConstructor.kt

@@ -40,9 +40,8 @@ internal class PersistentIrConstructor(
     override val isExternal: Boolean,
     override val isPrimary: Boolean,
     override val isExpect: Boolean
-) :
+) : IrConstructor(),
     PersistentIrDeclarationBase<ConstructorCarrier>,
-    IrConstructor,
     ConstructorCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrEnumEntry.kt

@@ -32,8 +32,8 @@ internal class PersistentIrEnumEntry(
     origin: IrDeclarationOrigin,
     override val symbol: IrEnumEntrySymbol,
     override val name: Name
-) : PersistentIrDeclarationBase<EnumEntryCarrier>,
+) : IrEnumEntry(),
-    IrEnumEntry,
+    PersistentIrDeclarationBase<EnumEntryCarrier>,
     EnumEntryCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrErrorDeclaration.kt

@@ -31,7 +31,7 @@ internal class PersistentIrErrorDeclaration(
     override val startOffset: Int,
     override val endOffset: Int,
     override val descriptor: DeclarationDescriptor
-) : PersistentIrDeclarationBase<ErrorCarrier>, IrErrorDeclaration, ErrorCarrier {
+) : PersistentIrDeclarationBase<ErrorCarrier>, IrErrorDeclaration(), ErrorCarrier {
     override var lastModified: Int = stageController.currentStage
     override var loweredUpTo: Int = stageController.currentStage
     override var values: Array<Carrier>? = null

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrField.kt

@@ -40,8 +40,8 @@ internal class PersistentIrField(
     override val isFinal: Boolean,
     override val isExternal: Boolean,
     override val isStatic: Boolean
-) : PersistentIrDeclarationBase<FieldCarrier>,
+) : IrField(),
-    IrField,
+    PersistentIrDeclarationBase<FieldCarrier>,
     FieldCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrFunction.kt

@@ -34,9 +34,8 @@ internal abstract class PersistentIrFunctionCommon(
     override val isOperator: Boolean,
     override val isInfix: Boolean,
     override val isExpect: Boolean,
-) :
+) : IrSimpleFunction(),
     PersistentIrDeclarationBase<FunctionCarrier>,
-    IrSimpleFunction,
     FunctionCarrier {
 
     override var lastModified: Int = stageController.currentStage

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrLocalDelegatedProperty.kt

@@ -37,7 +37,7 @@ internal class PersistentIrLocalDelegatedProperty(
     override val isVar: Boolean
 ) :
     PersistentIrDeclarationBase<LocalDelegatedPropertyCarrier>,
-    IrLocalDelegatedProperty,
+    IrLocalDelegatedProperty(),
     LocalDelegatedPropertyCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrProperty.kt

@@ -40,8 +40,8 @@ internal abstract class PersistentIrPropertyCommon(
     override val isDelegated: Boolean,
     override val isExternal: Boolean,
     override val isExpect: Boolean,
-) : PersistentIrDeclarationBase<PropertyCarrier>,
+) : IrProperty(),
-    IrProperty,
+    PersistentIrDeclarationBase<PropertyCarrier>,
     PropertyCarrier {
 
     override var lastModified: Int = stageController.currentStage

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrTypeAlias.kt

@@ -25,9 +25,8 @@ internal class PersistentIrTypeAlias(
     override val expandedType: IrType,
     override val isActual: Boolean,
     origin: IrDeclarationOrigin
-) :
+) : IrTypeAlias(),
     PersistentIrDeclarationBase<TypeAliasCarrier>,
-    IrTypeAlias,
     TypeAliasCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrTypeParameter.kt

@@ -40,9 +40,8 @@ internal class PersistentIrTypeParameter(
     override val index: Int,
     override val isReified: Boolean,
     override val variance: Variance
-) :
+) : IrTypeParameter(),
     PersistentIrDeclarationBase<TypeParameterCarrier>,
-    IrTypeParameter,
     TypeParameterCarrier {
 
     init {

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrValueParameter.kt

@@ -41,9 +41,8 @@ internal class PersistentIrValueParameter(
     override val varargElementType: IrType?,
     override val isCrossinline: Boolean,
     override val isNoinline: Boolean
-) :
+) : IrValueParameter(),
     PersistentIrDeclarationBase<ValueParameterCarrier>,
-    IrValueParameter,
     ValueParameterCarrier {
 
     @ObsoleteDescriptorBasedAPI

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrAnonymousInitializer.kt

@@ -23,12 +23,13 @@ import org.jetbrains.kotlin.ir.symbols.IrAnonymousInitializerSymbol
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrAnonymousInitializer : IrSymbolDeclaration<IrAnonymousInitializerSymbol> {
+abstract class IrAnonymousInitializer : IrSymbolDeclaration<IrAnonymousInitializerSymbol> {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: ClassDescriptor // TODO special descriptor for anonymous initializer blocks
+    abstract override val descriptor: ClassDescriptor // TODO special descriptor for anonymous initializer blocks
-    val isStatic: Boolean
 
-    var body: IrBlockBody
+    abstract val isStatic: Boolean
+
+    abstract var body: IrBlockBody
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitAnonymousInitializer(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt

@@ -28,28 +28,28 @@ import org.jetbrains.kotlin.ir.util.transformIfNeeded
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrClass :
+abstract class IrClass :
     IrSymbolDeclaration<IrClassSymbol>, IrDeclarationWithName, IrDeclarationWithVisibility,
     IrDeclarationContainer, IrTypeParametersContainer, IrAttributeContainer, IrMetadataSourceOwner {
 
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: ClassDescriptor
+    abstract override val descriptor: ClassDescriptor
 
-    val kind: ClassKind
+    abstract val kind: ClassKind
-    var modality: Modality
+    abstract var modality: Modality
-    val isCompanion: Boolean
+    abstract val isCompanion: Boolean
-    val isInner: Boolean
+    abstract val isInner: Boolean
-    val isData: Boolean
+    abstract val isData: Boolean
-    val isExternal: Boolean
+    abstract val isExternal: Boolean
-    val isInline: Boolean
+    abstract val isInline: Boolean
-    val isExpect: Boolean
+    abstract val isExpect: Boolean
-    val isFun: Boolean
+    abstract val isFun: Boolean
 
-    val source: SourceElement
+    abstract val source: SourceElement
 
-    var superTypes: List<IrType>
+    abstract var superTypes: List<IrType>
 
-    var thisReceiver: IrValueParameter?
+    abstract var thisReceiver: IrValueParameter?
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitClass(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrConstructor.kt

@@ -21,11 +21,11 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrConstructor : IrFunction, IrSymbolDeclaration<IrConstructorSymbol> {
+abstract class IrConstructor : IrFunction(), IrSymbolDeclaration<IrConstructorSymbol> {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: ClassConstructorDescriptor
+    abstract override val descriptor: ClassConstructorDescriptor
 
-    val isPrimary: Boolean
+    abstract val isPrimary: Boolean
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitConstructor(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrEnumEntry.kt

@@ -23,12 +23,12 @@ import org.jetbrains.kotlin.ir.symbols.IrEnumEntrySymbol
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrEnumEntry : IrSymbolDeclaration<IrEnumEntrySymbol>, IrDeclarationWithName {
+abstract class IrEnumEntry : IrSymbolDeclaration<IrEnumEntrySymbol>, IrDeclarationWithName {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: ClassDescriptor
+    abstract override val descriptor: ClassDescriptor
 
-    var correspondingClass: IrClass?
+    abstract var correspondingClass: IrClass?
-    var initializerExpression: IrExpressionBody?
+    abstract var initializerExpression: IrExpressionBody?
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitEnumEntry(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrErrorDeclaration.kt

@@ -19,7 +19,7 @@ package org.jetbrains.kotlin.ir.declarations
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrErrorDeclaration : IrDeclaration {
+abstract class IrErrorDeclaration : IrDeclaration {
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitErrorDeclaration(this, data)
 

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrField.kt

@@ -14,21 +14,21 @@ import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrField :
+abstract class IrField :
     IrSymbolDeclaration<IrFieldSymbol>,
     IrDeclarationWithName, IrDeclarationWithVisibility, IrDeclarationParent, IrMetadataSourceOwner {
 
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: PropertyDescriptor
+    abstract override val descriptor: PropertyDescriptor
 
-    val type: IrType
+    abstract val type: IrType
-    val isFinal: Boolean
+    abstract val isFinal: Boolean
-    val isExternal: Boolean
+    abstract val isExternal: Boolean
-    val isStatic: Boolean
+    abstract val isStatic: Boolean
 
-    var initializer: IrExpressionBody?
+    abstract var initializer: IrExpressionBody?
 
-    var correspondingPropertySymbol: IrPropertySymbol?
+    abstract var correspondingPropertySymbol: IrPropertySymbol?
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitField(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFunction.kt

@@ -27,25 +27,25 @@ import org.jetbrains.kotlin.ir.util.transformIfNeeded
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrFunction :
+abstract class IrFunction :
     IrDeclarationWithName, IrDeclarationWithVisibility, IrTypeParametersContainer, IrSymbolOwner, IrDeclarationParent, IrReturnTarget,
     IrMetadataSourceOwner {
 
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: FunctionDescriptor
+    abstract override val descriptor: FunctionDescriptor
-    override val symbol: IrFunctionSymbol
+    abstract override val symbol: IrFunctionSymbol
 
-    val isInline: Boolean // NB: there's an inline constructor for Array and each primitive array class
+    abstract val isInline: Boolean // NB: there's an inline constructor for Array and each primitive array class
-    val isExternal: Boolean
+    abstract val isExternal: Boolean
-    val isExpect: Boolean
+    abstract val isExpect: Boolean
 
-    var returnType: IrType
+    abstract var returnType: IrType
 
-    var dispatchReceiverParameter: IrValueParameter?
+    abstract var dispatchReceiverParameter: IrValueParameter?
-    var extensionReceiverParameter: IrValueParameter?
+    abstract var extensionReceiverParameter: IrValueParameter?
-    var valueParameters: List<IrValueParameter>
+    abstract var valueParameters: List<IrValueParameter>
 
-    var body: IrBody?
+    abstract var body: IrBody?
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         typeParameters.forEach { it.accept(visitor, data) }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrLocalDelegatedProperty.kt

@@ -23,21 +23,21 @@ import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrLocalDelegatedProperty :
+abstract class IrLocalDelegatedProperty :
     IrDeclarationWithName,
     IrSymbolOwner,
     IrMetadataSourceOwner {
 
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: VariableDescriptorWithAccessors
+    abstract override val descriptor: VariableDescriptorWithAccessors
-    override val symbol: IrLocalDelegatedPropertySymbol
+    abstract override val symbol: IrLocalDelegatedPropertySymbol
 
-    val type: IrType
+    abstract val type: IrType
-    val isVar: Boolean
+    abstract val isVar: Boolean
 
-    var delegate: IrVariable
+    abstract var delegate: IrVariable
-    var getter: IrFunction
+    abstract var getter: IrFunction
-    var setter: IrFunction?
+    abstract var setter: IrFunction?
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitLocalDelegatedProperty(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrProperty.kt

@@ -22,22 +22,22 @@ import org.jetbrains.kotlin.ir.symbols.IrPropertySymbol
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrProperty : IrOverridableMember, IrMetadataSourceOwner {
+abstract class IrProperty : IrOverridableMember, IrMetadataSourceOwner {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: PropertyDescriptor
+    abstract override val descriptor: PropertyDescriptor
-    override val symbol: IrPropertySymbol
+    abstract override val symbol: IrPropertySymbol
 
-    val isVar: Boolean
+    abstract val isVar: Boolean
-    val isConst: Boolean
+    abstract val isConst: Boolean
-    val isLateinit: Boolean
+    abstract val isLateinit: Boolean
-    val isDelegated: Boolean
+    abstract val isDelegated: Boolean
-    val isExternal: Boolean
+    abstract val isExternal: Boolean
-    val isExpect: Boolean
+    abstract val isExpect: Boolean
-    val isFakeOverride: Boolean
+    abstract val isFakeOverride: Boolean
 
-    var backingField: IrField?
+    abstract var backingField: IrField?
-    var getter: IrSimpleFunction?
+    abstract var getter: IrSimpleFunction?
-    var setter: IrSimpleFunction?
+    abstract var setter: IrSimpleFunction?
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitProperty(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrScript.kt

@@ -10,9 +10,9 @@ import org.jetbrains.kotlin.ir.symbols.IrScriptSymbol
 
 //TODO: make IrScript as IrPackageFragment, because script is used as a file, not as a class
 //NOTE: declarations and statements stored separately
-interface IrScript : IrSymbolDeclaration<IrScriptSymbol>, IrDeclarationContainer, IrDeclarationWithName, IrDeclarationParent {
+abstract class IrScript : IrSymbolDeclaration<IrScriptSymbol>, IrDeclarationContainer, IrDeclarationWithName, IrDeclarationParent {
-    val statements: MutableList<IrStatement>
+    abstract val statements: MutableList<IrStatement>
 
     // NOTE: is the result of the FE conversion, because there script interpreted as a class and has receiver
-    var thisReceiver: IrValueParameter
+    abstract var thisReceiver: IrValueParameter
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrSimpleFunction.kt

@@ -9,20 +9,20 @@ import org.jetbrains.kotlin.ir.symbols.IrPropertySymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrSimpleFunction :
+abstract class IrSimpleFunction :
-    IrFunction,
+    IrFunction(),
     IrSymbolDeclaration<IrSimpleFunctionSymbol>,
     IrOverridableDeclaration<IrSimpleFunctionSymbol>,
     IrOverridableMember,
     IrAttributeContainer {
 
-    val isTailrec: Boolean
+    abstract val isTailrec: Boolean
-    val isSuspend: Boolean
+    abstract val isSuspend: Boolean
-    val isFakeOverride: Boolean
+    abstract val isFakeOverride: Boolean
-    val isOperator: Boolean
+    abstract val isOperator: Boolean
-    val isInfix: Boolean
+    abstract val isInfix: Boolean
 
-    var correspondingPropertySymbol: IrPropertySymbol?
+    abstract var correspondingPropertySymbol: IrPropertySymbol?
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitSimpleFunction(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrTypeAlias.kt

@@ -13,17 +13,17 @@ import org.jetbrains.kotlin.ir.util.transformIfNeeded
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrTypeAlias :
+abstract class IrTypeAlias :
     IrSymbolDeclaration<IrTypeAliasSymbol>,
     IrDeclarationWithName,
     IrDeclarationWithVisibility,
     IrTypeParametersContainer {
 
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: TypeAliasDescriptor
+    abstract override val descriptor: TypeAliasDescriptor
 
-    val isActual: Boolean
+    abstract val isActual: Boolean
-    val expandedType: IrType
+    abstract val expandedType: IrType
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitTypeAlias(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrTypeParameter.kt

@@ -24,14 +24,14 @@ import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.Variance
 
-interface IrTypeParameter : IrSymbolDeclaration<IrTypeParameterSymbol>, IrDeclarationWithName {
+abstract class IrTypeParameter : IrSymbolDeclaration<IrTypeParameterSymbol>, IrDeclarationWithName {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: TypeParameterDescriptor
+    abstract override val descriptor: TypeParameterDescriptor
 
-    val variance: Variance
+    abstract val variance: Variance
-    val index: Int
+    abstract val index: Int
-    val isReified: Boolean
+    abstract val isReified: Boolean
-    val superTypes: MutableList<IrType>
+    abstract val superTypes: MutableList<IrType>
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitTypeParameter(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrValueDeclaration.kt

@@ -10,10 +10,10 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.symbols.IrValueSymbol
 import org.jetbrains.kotlin.ir.types.IrType
 
-interface IrValueDeclaration : IrDeclarationWithName, IrSymbolOwner {
+abstract class IrValueDeclaration : IrDeclarationWithName, IrSymbolOwner {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: ValueDescriptor
+    abstract override val descriptor: ValueDescriptor
 
-    override val symbol: IrValueSymbol
+    abstract override val symbol: IrValueSymbol
-    val type: IrType
+    abstract val type: IrType
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrValueParameter.kt

@@ -24,16 +24,16 @@ import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-interface IrValueParameter : IrValueDeclaration, IrSymbolDeclaration<IrValueParameterSymbol> {
+abstract class IrValueParameter : IrValueDeclaration(), IrSymbolDeclaration<IrValueParameterSymbol> {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: ParameterDescriptor
+    abstract override val descriptor: ParameterDescriptor
 
-    val index: Int
+    abstract val index: Int
-    val varargElementType: IrType?
+    abstract val varargElementType: IrType?
-    val isCrossinline: Boolean
+    abstract val isCrossinline: Boolean
-    val isNoinline: Boolean
+    abstract val isNoinline: Boolean
 
-    var defaultValue: IrExpressionBody?
+    abstract var defaultValue: IrExpressionBody?
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
         visitor.visitValueParameter(this, data)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrVariable.kt

@@ -21,14 +21,13 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.symbols.IrVariableSymbol
 
-interface IrVariable : IrValueDeclaration, IrSymbolDeclaration<IrVariableSymbol> {
+abstract class IrVariable : IrValueDeclaration(), IrSymbolDeclaration<IrVariableSymbol> {
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: VariableDescriptor
+    abstract override val descriptor: VariableDescriptor
 
-    val isVar: Boolean
+    abstract val isVar: Boolean
-    val isConst: Boolean
+    abstract val isConst: Boolean
-    val isLateinit: Boolean
+    abstract val isLateinit: Boolean
 
-    var initializer: IrExpression?
+    abstract var initializer: IrExpression?
 }
-

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrScriptImpl.kt

@@ -23,7 +23,7 @@ private val SCRIPT_ORIGIN = object : IrDeclarationOriginImpl("FIELD_FOR_OBJECT_I
 class IrScriptImpl(
     override val symbol: IrScriptSymbol,
     override val name: Name
-) : IrScript, IrDeclaration {
+) : IrScript() {
     override val startOffset: Int get() = UNDEFINED_OFFSET
     override val endOffset: Int get() = UNDEFINED_OFFSET
     override var origin: IrDeclarationOrigin = SCRIPT_ORIGIN
@@ -44,7 +44,8 @@ class IrScriptImpl(
     override lateinit var thisReceiver: IrValueParameter
 
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: ScriptDescriptor = symbol.descriptor
+    override val descriptor: ScriptDescriptor
+        get() = symbol.descriptor
 
     override val factory: IrFactory
         get() = error("Create IrScriptImpl directly")

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrVariableImpl.kt

@@ -40,8 +40,7 @@ class IrVariableImpl(
     override val isVar: Boolean,
     override val isConst: Boolean,
     override val isLateinit: Boolean
-) : IrVariable {
+) : IrVariable() {
-
     private var _parent: IrDeclarationParent? = null
     override var parent: IrDeclarationParent
         get() = _parent
@@ -57,7 +56,8 @@ class IrVariableImpl(
     }
 
     @ObsoleteDescriptorBasedAPI
-    override val descriptor: VariableDescriptor get() = symbol.descriptor
+    override val descriptor: VariableDescriptor
+        get() = symbol.descriptor
 
     override var initializer: IrExpression? = null
 

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt

@@ -38,7 +38,7 @@ class IrLazyClass(
     override val isFun: Boolean,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator
-) : IrClass, IrLazyDeclarationBase {
+) : IrClass(), IrLazyDeclarationBase {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyConstructor.kt

@@ -33,7 +33,7 @@ class IrLazyConstructor(
     override val isExpect: Boolean,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator,
-) : IrConstructor, IrLazyFunctionBase {
+) : IrConstructor(), IrLazyFunctionBase {
     override var parent: IrDeclarationParent by createLazyParent()
 
     override var annotations: List<IrConstructorCall> by createLazyAnnotations()

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyEnumEntryImpl.kt

@@ -38,7 +38,7 @@ class IrLazyEnumEntryImpl(
     override val descriptor: ClassDescriptor,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator,
-) : IrEnumEntry, IrLazyDeclarationBase {
+) : IrEnumEntry(), IrLazyDeclarationBase {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyField.kt

@@ -36,7 +36,7 @@ class IrLazyField(
     override val isStatic: Boolean,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator,
-) : IrField, IrLazyDeclarationBase {
+) : IrField(), IrLazyDeclarationBase {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyFunction.kt

@@ -41,7 +41,7 @@ class IrLazyFunction(
     override val isInfix: Boolean,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator,
-) : IrSimpleFunction, IrLazyFunctionBase {
+) : IrSimpleFunction(), IrLazyFunctionBase {
     override var parent: IrDeclarationParent by createLazyParent()
 
     override var annotations: List<IrConstructorCall> by createLazyAnnotations()

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyProperty.kt

@@ -38,7 +38,7 @@ class IrLazyProperty(
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator,
     bindingContext: BindingContext? = null
-) : IrProperty, IrLazyDeclarationBase {
+) : IrProperty(), IrLazyDeclarationBase {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyTypeAlias.kt

@@ -28,7 +28,7 @@ class IrLazyTypeAlias(
     override val isActual: Boolean,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator,
-) : IrTypeAlias, IrLazyDeclarationBase {
+) : IrTypeAlias(), IrLazyDeclarationBase {
     init {
         symbol.bind(this)
     }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyTypeParameter.kt

@@ -29,7 +29,7 @@ class IrLazyTypeParameter(
     override val variance: Variance,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator,
-) : IrTypeParameter, IrLazyDeclarationBase {
+) : IrTypeParameter(), IrLazyDeclarationBase {
     init {
         symbol.bind(this)
     }