JVM IR: generate delegates to DefaultImpls for fun interfaces

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

@@ -485,7 +485,7 @@ val IrFunction.allParameters: List<IrValueParameter>
         explicitParameters
     }
 
-fun IrClass.addFakeOverrides(implementedMembers: List<IrSimpleFunction> = emptyList()) {
+fun IrClass.addFakeOverridesViaIncorrectHeuristic(implementedMembers: List<IrSimpleFunction> = emptyList()) {
     fun IrDeclaration.toList() = when (this) {
         is IrSimpleFunction -> listOf(this)
         is IrProperty -> listOfNotNull(getter, setter)
@@ -519,7 +519,7 @@ fun IrClass.addFakeOverrides(implementedMembers: List<IrSimpleFunction> = emptyL
                 IrDeclarationOrigin.FAKE_OVERRIDE,
                 IrSimpleFunctionSymbolImpl(descriptor),
                 irFunction.name,
-                Visibilities.INHERITED,
+                Visibilities.PUBLIC,
                 irFunction.modality,
                 irFunction.returnType,
                 isInline = irFunction.isInline,
@@ -531,7 +531,7 @@ fun IrClass.addFakeOverrides(implementedMembers: List<IrSimpleFunction> = emptyL
                 isOperator = irFunction.isOperator
             ).apply {
                 descriptor.bind(this)
-                parent = this@addFakeOverrides
+                parent = this@addFakeOverridesViaIncorrectHeuristic
                 overriddenSymbols = overriddenFunctions.map { it.symbol }
                 copyParameterDeclarationsFrom(irFunction)
                 copyAttributes(irFunction)

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt

@@ -367,7 +367,7 @@ abstract class AbstractSuspendFunctionsLowering<C : CommonBackendContext>(val co
             }
 
             coroutineClass.superTypes += superTypes
-            coroutineClass.addFakeOverrides()
+            coroutineClass.addFakeOverridesViaIncorrectHeuristic()
 
             initializeStateMachine(coroutineConstructors, coroutineClassThis)
 

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/SingleAbstractMethodLowering.kt

@@ -8,7 +8,7 @@ package org.jetbrains.kotlin.backend.common.lower
 import org.jetbrains.kotlin.backend.common.CommonBackendContext
 import org.jetbrains.kotlin.backend.common.FileLoweringPass
 import org.jetbrains.kotlin.backend.common.IrElementTransformerVoidWithContext
-import org.jetbrains.kotlin.backend.common.ir.addFakeOverrides
+import org.jetbrains.kotlin.backend.common.ir.addFakeOverridesViaIncorrectHeuristic
 import org.jetbrains.kotlin.backend.common.ir.copyTo
 import org.jetbrains.kotlin.backend.common.ir.createImplicitParameterDeclarationWithWrappedDescriptor
 import org.jetbrains.kotlin.descriptors.ClassKind
@@ -215,7 +215,7 @@ abstract class SingleAbstractMethodLowering(val context: CommonBackendContext) :
 
         generateEqualsHashCode(subclass, superType, field)
 
-        subclass.addFakeOverrides()
+        subclass.addFakeOverridesViaIncorrectHeuristic()
 
         return subclass
     }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/coroutines/AbstractSuspendFunctionsLowering.kt

@@ -468,7 +468,7 @@ abstract class AbstractSuspendFunctionsLowering<C : CommonBackendContext>(val co
                 coroutineClass.superTypes += coroutineBaseClass.defaultType
             }
 
-            coroutineClass.addFakeOverrides(implementedMembers)
+            coroutineClass.addFakeOverridesViaIncorrectHeuristic(implementedMembers)
 
             // TODO: to meet PIR lower model constructor modification shouldn't be performed here
             initializeStateMachine(listOf(coroutineConstructor), coroutineClassThis)

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/FunctionReferenceLowering.kt

@@ -7,10 +7,7 @@ package org.jetbrains.kotlin.backend.jvm.lower
 
 import org.jetbrains.kotlin.backend.common.FileLoweringPass
 import org.jetbrains.kotlin.backend.common.IrElementTransformerVoidWithContext
-import org.jetbrains.kotlin.backend.common.ir.copyTo
+import org.jetbrains.kotlin.backend.common.ir.*
-import org.jetbrains.kotlin.backend.common.ir.createImplicitParameterDeclarationWithWrappedDescriptor
-import org.jetbrains.kotlin.backend.common.ir.isSuspend
-import org.jetbrains.kotlin.backend.common.ir.moveBodyTo
 import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
 import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
 import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
@@ -150,10 +147,11 @@ internal class FunctionReferenceLowering(private val context: JvmBackendContext)
         private val adaptedReferenceOriginalTarget: IrFunction? = adapteeCall?.symbol?.owner
         private val isAdaptedReference = adaptedReferenceOriginalTarget != null
 
+        private val isKotlinFunInterface =
+            samSuperType != null && samSuperType.getClass()?.origin != IrDeclarationOrigin.IR_EXTERNAL_JAVA_DECLARATION_STUB
+
         private val needToGenerateSamEqualsHashCodeMethods =
-            samSuperType != null &&
+            isKotlinFunInterface && (isAdaptedReference || !isLambda)
-                    samSuperType.getClass()?.origin != IrDeclarationOrigin.IR_EXTERNAL_JAVA_DECLARATION_STUB &&
-                    (isAdaptedReference || !isLambda)
 
         private val superType =
             samSuperType ?: when {
@@ -229,6 +227,9 @@ internal class FunctionReferenceLowering(private val context: JvmBackendContext)
                 if (needToGenerateSamEqualsHashCodeMethods) {
                     generateSamEqualsHashCodeMethods(boundReceiverVar)
                 }
+                if (isKotlinFunInterface) {
+                    functionReferenceClass.addFakeOverridesViaIncorrectHeuristic()
+                }
 
                 +functionReferenceClass
                 +irCall(constructor.symbol).apply {

compiler/testData/codegen/box/funInterface/funInterfaceInheritance.kt

@@ -1,5 +1,4 @@
 // !LANGUAGE: +NewInference +FunctionalInterfaceConversion +SamConversionPerArgument +SamConversionForKotlinFunctions
-// IGNORE_BACKEND: JVM_IR
 // IGNORE_BACKEND_FIR: JVM_IR
 // SKIP_DCE_DRIVEN
 

compiler/testData/codegen/box/funInterface/nonAbstractMethod.kt

@@ -1,4 +1,4 @@
-// IGNORE_BACKEND: JVM_IR, JS_IR
+// IGNORE_BACKEND: JS_IR
 // IGNORE_BACKEND_FIR: JVM_IR
 
 interface I {