[FIR] Properly detect callable reference type according conversions

compiler/fir/cones/src/org/jetbrains/kotlin/fir/symbols/StandardClassIds.kt

@@ -42,6 +42,7 @@ object StandardClassIds {
     val String = "String".baseId()
 
     val KProperty = "KProperty".reflectId()
+    val KMutableProperty = "KMutableProperty".reflectId()
     val KProperty0 = "KProperty0".reflectId()
     val KMutableProperty0 = "KMutableProperty0".reflectId()
     val KProperty1 = "KProperty1".reflectId()
@@ -50,6 +51,7 @@ object StandardClassIds {
     val KMutableProperty2 = "KMutableProperty2".reflectId()
     val KFunction = "KFunction".reflectId()
     val KClass = "KClass".reflectId()
+    val KCallable = "KCallable".reflectId()
 
     val Comparable = "Comparable".baseId()
     val Number = "Number".baseId()

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/CallableReferenceResolution.kt

@@ -0,0 +1,402 @@
+/*
+ * Copyright 2010-2020 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.fir.resolve.calls
+
+import org.jetbrains.kotlin.fir.FirElement
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.FirSourceElement
+import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.expressions.FirAnnotationCall
+import org.jetbrains.kotlin.fir.expressions.FirExpression
+import org.jetbrains.kotlin.fir.expressions.FirNamedArgumentExpression
+import org.jetbrains.kotlin.fir.expressions.FirResolvedQualifier
+import org.jetbrains.kotlin.fir.expressions.builder.buildNamedArgumentExpression
+import org.jetbrains.kotlin.fir.resolve.DoubleColonLHS
+import org.jetbrains.kotlin.fir.resolve.createFunctionalType
+import org.jetbrains.kotlin.fir.resolve.diagnostics.ConeUnsupportedCallableReferenceTarget
+import org.jetbrains.kotlin.fir.resolve.inference.extractInputOutputTypesFromCallableReferenceExpectedType
+import org.jetbrains.kotlin.fir.resolve.inference.isSuspendFunctionType
+import org.jetbrains.kotlin.fir.symbols.StandardClassIds
+import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
+import org.jetbrains.kotlin.fir.types.*
+import org.jetbrains.kotlin.fir.visitors.FirTransformer
+import org.jetbrains.kotlin.fir.visitors.FirVisitor
+import org.jetbrains.kotlin.resolve.calls.components.SuspendConversionStrategy
+import org.jetbrains.kotlin.resolve.calls.inference.ConstraintSystemOperation
+import org.jetbrains.kotlin.resolve.calls.inference.model.SimpleConstraintSystemConstraintPosition
+import org.jetbrains.kotlin.resolve.calls.tower.isSuccess
+import org.jetbrains.kotlin.types.expressions.CoercionStrategy
+
+
+internal object CheckCallableReferenceExpectedType : CheckerStage() {
+    override suspend fun check(candidate: Candidate, callInfo: CallInfo, sink: CheckerSink, context: ResolutionContext) {
+        val outerCsBuilder = callInfo.outerCSBuilder ?: return
+        val expectedType = callInfo.expectedType
+        if (candidate.symbol !is FirCallableSymbol<*>) return
+
+        val resultingReceiverType = when (callInfo.lhs) {
+            is DoubleColonLHS.Type -> callInfo.lhs.type.takeIf { callInfo.explicitReceiver !is FirResolvedQualifier }
+            else -> null
+        }
+
+        val fir: FirCallableDeclaration<*> = candidate.symbol.fir
+
+        val (rawResultingType, callableReferenceAdaptation) = buildReflectionType(fir, resultingReceiverType, callInfo, context)
+        val resultingType = candidate.substitutor.substituteOrSelf(rawResultingType)
+
+        if (callableReferenceAdaptation.needCompatibilityResolveForCallableReference()) {
+            sink.reportDiagnostic(LowerPriorityToPreserveCompatibilityDiagnostic)
+        }
+
+        candidate.resultingTypeForCallableReference = resultingType
+        candidate.usesSuspendConversion =
+            callableReferenceAdaptation?.suspendConversionStrategy == SuspendConversionStrategy.SUSPEND_CONVERSION
+        candidate.outerConstraintBuilderEffect = fun ConstraintSystemOperation.() {
+            addOtherSystem(candidate.system.asReadOnlyStorage())
+
+            val position = SimpleConstraintSystemConstraintPosition //TODO
+
+            if (expectedType != null) {
+                addSubtypeConstraint(resultingType, expectedType, position)
+            }
+
+            val declarationReceiverType: ConeKotlinType? =
+                (fir as? FirCallableMemberDeclaration<*>)?.receiverTypeRef?.coneType
+                    ?.let(candidate.substitutor::substituteOrSelf)
+
+            if (resultingReceiverType != null && declarationReceiverType != null) {
+                addSubtypeConstraint(resultingReceiverType, declarationReceiverType, position)
+            }
+        }
+
+        var isApplicable = true
+
+        outerCsBuilder.runTransaction {
+            candidate.outerConstraintBuilderEffect!!(this)
+
+            isApplicable = !hasContradiction
+
+            false
+        }
+
+        if (!isApplicable) {
+            sink.yieldDiagnostic(InapplicableCandidate)
+        }
+    }
+}
+
+
+/*
+val resultingReceiverType = when (callInfo.lhs) {
+    is DoubleColonLHS.Type -> callInfo.lhs.type.takeIf { callInfo.explicitReceiver !is FirResolvedQualifier }
+    else -> null
+}
+ */
+private fun buildReflectionType(
+    fir: FirCallableDeclaration<*>,
+    receiverType: ConeKotlinType?,
+    callInfo: CallInfo,
+    context: ResolutionContext
+): Pair<ConeKotlinType, CallableReferenceAdaptation?> {
+    val returnTypeRef = context.bodyResolveComponents.returnTypeCalculator.tryCalculateReturnType(fir)
+    return when (fir) {
+        is FirFunction -> {
+            val unboundReferenceTarget = if (receiverType != null) 1 else 0
+            val callableReferenceAdaptation =
+                getCallableReferenceAdaptation(context.session, fir, callInfo.expectedType, unboundReferenceTarget)
+
+            val parameters = mutableListOf<ConeKotlinType>()
+
+            val returnType = callableReferenceAdaptation?.let {
+                parameters += it.argumentTypes
+                if (it.coercionStrategy == CoercionStrategy.COERCION_TO_UNIT) {
+                    context.session.builtinTypes.unitType.type
+                } else {
+                    returnTypeRef.coneType
+                }
+            } ?: returnTypeRef.coneType.also {
+                fir.valueParameters.mapTo(parameters) { it.returnTypeRef.coneType }
+            }
+
+            val isSuspend = (fir as? FirSimpleFunction)?.isSuspend == true ||
+                    callableReferenceAdaptation?.suspendConversionStrategy == SuspendConversionStrategy.SUSPEND_CONVERSION
+            return createFunctionalType(
+                parameters,
+                receiverType = receiverType,
+                rawReturnType = returnType,
+                isKFunctionType = true,
+                isSuspend = isSuspend
+            ) to callableReferenceAdaptation
+        }
+        is FirVariable -> createKPropertyType(fir, receiverType, returnTypeRef) to null
+        else -> ConeClassErrorType(ConeUnsupportedCallableReferenceTarget(fir)) to null
+    }
+}
+
+internal class CallableReferenceAdaptation(
+    val argumentTypes: Array<ConeKotlinType>,
+    val coercionStrategy: CoercionStrategy,
+    val defaults: Int,
+    val mappedArguments: Map<FirValueParameter, ResolvedCallArgument>,
+    val suspendConversionStrategy: SuspendConversionStrategy
+)
+
+private fun CallableReferenceAdaptation?.needCompatibilityResolveForCallableReference(): Boolean {
+    // KT-13934: check containing declaration for companion object
+    if (this == null) return false
+    return defaults != 0 ||
+            suspendConversionStrategy != SuspendConversionStrategy.NO_CONVERSION ||
+            coercionStrategy != CoercionStrategy.NO_COERCION ||
+            mappedArguments.values.any { it is ResolvedCallArgument.VarargArgument }
+}
+
+private fun getCallableReferenceAdaptation(
+    session: FirSession,
+    function: FirFunction<*>,
+    expectedType: ConeKotlinType?,
+    unboundReceiverCount: Int
+): CallableReferenceAdaptation? {
+    if (expectedType == null) return null
+
+    // Do not adapt references against KCallable type as it's impossible to map defaults/vararg to absent parameters of KCallable
+    if (expectedType.isKCallableType()) return null
+
+    val (inputTypes, returnExpectedType) = extractInputOutputTypesFromCallableReferenceExpectedType(expectedType, session) ?: return null
+    val expectedArgumentsCount = inputTypes.size - unboundReceiverCount
+    if (expectedArgumentsCount < 0) return null
+
+    val fakeArguments = createFakeArgumentsForReference(function, expectedArgumentsCount, inputTypes, unboundReceiverCount)
+    val argumentMapping = mapArguments(fakeArguments, function)
+    if (argumentMapping.diagnostics.any { !it.applicability.isSuccess }) return null
+
+    /**
+     * (A, B, C) -> Unit
+     * fun foo(a: A, b: B = B(), vararg c: C)
+     */
+    var defaults = 0
+    var varargMappingState = VarargMappingState.UNMAPPED
+    val mappedArguments = linkedMapOf<FirValueParameter, ResolvedCallArgument>()
+    val mappedVarargElements = linkedMapOf<FirValueParameter, MutableList<FirExpression>>()
+    val mappedArgumentTypes = arrayOfNulls<ConeKotlinType?>(fakeArguments.size)
+
+    for ((valueParameter, resolvedArgument) in argumentMapping.parameterToCallArgumentMap) {
+        for (fakeArgument in resolvedArgument.arguments) {
+            val index = fakeArgument.index
+            val substitutedParameter = function.valueParameters.getOrNull(function.indexOf(valueParameter)) ?: continue
+
+            val mappedArgument: ConeKotlinType?
+            if (substitutedParameter.isVararg) {
+                val (varargType, newVarargMappingState) = varargParameterTypeByExpectedParameter(
+                    inputTypes[index + unboundReceiverCount],
+                    substitutedParameter,
+                    varargMappingState
+                )
+                varargMappingState = newVarargMappingState
+                mappedArgument = varargType
+
+                when (newVarargMappingState) {
+                    VarargMappingState.MAPPED_WITH_ARRAY -> {
+                        // If we've already mapped an argument to this value parameter, it'll always be a type mismatch.
+                        mappedArguments[valueParameter] = ResolvedCallArgument.SimpleArgument(fakeArgument)
+                    }
+                    VarargMappingState.MAPPED_WITH_PLAIN_ARGS -> {
+                        mappedVarargElements.getOrPut(valueParameter) { ArrayList() }.add(fakeArgument)
+                    }
+                    VarargMappingState.UNMAPPED -> {
+                    }
+                }
+            } else {
+                mappedArgument = substitutedParameter.returnTypeRef.coneType
+                mappedArguments[valueParameter] = resolvedArgument
+            }
+
+            mappedArgumentTypes[index] = mappedArgument
+        }
+        if (resolvedArgument == ResolvedCallArgument.DefaultArgument) {
+            defaults++
+            mappedArguments[valueParameter] = resolvedArgument
+        }
+    }
+    if (mappedArgumentTypes.any { it == null }) return null
+
+    for ((valueParameter, varargElements) in mappedVarargElements) {
+        mappedArguments[valueParameter] = ResolvedCallArgument.VarargArgument(varargElements)
+    }
+
+    for (valueParameter in function.valueParameters) {
+        if (valueParameter.isVararg && valueParameter !in mappedArguments) {
+            mappedArguments[valueParameter] = ResolvedCallArgument.VarargArgument(emptyList())
+        }
+    }
+
+    val coercionStrategy = if (returnExpectedType.isUnit && !function.returnTypeRef.isUnit)
+        CoercionStrategy.COERCION_TO_UNIT
+    else
+        CoercionStrategy.NO_COERCION
+
+    val adaptedArguments = if (expectedType.isBaseTypeForNumberedReferenceTypes)
+        emptyMap()
+    else
+        mappedArguments
+
+    val suspendConversionStrategy = if ((function as? FirSimpleFunction)?.isSuspend != true && expectedType.isSuspendFunctionType(session))
+        SuspendConversionStrategy.SUSPEND_CONVERSION
+    else
+        SuspendConversionStrategy.NO_CONVERSION
+
+    @Suppress("UNCHECKED_CAST")
+    return CallableReferenceAdaptation(
+        mappedArgumentTypes as Array<ConeKotlinType>,
+        coercionStrategy,
+        defaults,
+        adaptedArguments,
+        suspendConversionStrategy
+    )
+}
+
+fun ConeKotlinType?.isPotentiallyArray(): Boolean =
+    this != null && (this.arrayElementType() != null || this is ConeTypeVariableType)
+
+private fun varargParameterTypeByExpectedParameter(
+    expectedParameterType: ConeKotlinType,
+    substitutedParameter: FirValueParameter,
+    varargMappingState: VarargMappingState,
+): Pair<ConeKotlinType?, VarargMappingState> {
+    val elementType = substitutedParameter.returnTypeRef.coneType.arrayElementType()
+        ?: error("Vararg parameter $substitutedParameter does not have vararg type")
+
+    return when (varargMappingState) {
+        VarargMappingState.UNMAPPED -> {
+            if (expectedParameterType.isPotentiallyArray()) {
+                elementType.createOutArrayType() to VarargMappingState.MAPPED_WITH_ARRAY
+            } else {
+                elementType to VarargMappingState.MAPPED_WITH_PLAIN_ARGS
+            }
+        }
+        VarargMappingState.MAPPED_WITH_PLAIN_ARGS -> {
+            if (expectedParameterType.isPotentiallyArray())
+                null to VarargMappingState.MAPPED_WITH_PLAIN_ARGS
+            else
+                elementType to VarargMappingState.MAPPED_WITH_PLAIN_ARGS
+        }
+        VarargMappingState.MAPPED_WITH_ARRAY ->
+            null to VarargMappingState.MAPPED_WITH_ARRAY
+    }
+}
+
+
+private enum class VarargMappingState {
+    UNMAPPED, MAPPED_WITH_PLAIN_ARGS, MAPPED_WITH_ARRAY
+}
+
+private fun FirFunction<*>.indexOf(valueParameter: FirValueParameter): Int = valueParameters.indexOf(valueParameter)
+
+private val ConeKotlinType.isUnit: Boolean
+    get() {
+        val type = this.lowerBoundIfFlexible()
+        if (type.isNullable) return false
+        val classId = type.classId ?: return false
+        return classId == StandardClassIds.Unit
+    }
+
+private val ConeKotlinType.isBaseTypeForNumberedReferenceTypes: Boolean
+    get() {
+        val classId = lowerBoundIfFlexible().classId ?: return false
+        return when (classId) {
+            StandardClassIds.KProperty,
+            StandardClassIds.KMutableProperty,
+            StandardClassIds.KCallable -> true
+            else -> false
+        }
+    }
+
+private val FirExpression.index: Int
+    get() = when (this) {
+        is FirNamedArgumentExpression -> expression.index
+        is FirFakeArgumentForCallableReference -> index
+        else -> throw IllegalArgumentException()
+    }
+
+private fun createFakeArgumentsForReference(
+    function: FirFunction<*>,
+    expectedArgumentCount: Int,
+    inputTypes: List<ConeKotlinType>,
+    unboundReceiverCount: Int
+): List<FirExpression> {
+    var afterVararg = false
+    var varargComponentType: ConeKotlinType? = null
+    var vararg = false
+    return (0 until expectedArgumentCount).map { index ->
+        val inputType = inputTypes.getOrNull(index + unboundReceiverCount)
+        if (vararg && varargComponentType != inputType) {
+            afterVararg = true
+        }
+
+        val valueParameter = function.valueParameters.getOrNull(index)
+        val name = if (afterVararg && valueParameter?.defaultValue != null)
+            valueParameter.name
+        else
+            null
+
+        if (valueParameter?.isVararg == true) {
+            varargComponentType = inputType
+            vararg = true
+        }
+        if (name != null) {
+            buildNamedArgumentExpression {
+                expression = FirFakeArgumentForCallableReference(index)
+                this.name = name
+                isSpread = false
+            }
+        } else {
+            FirFakeArgumentForCallableReference(index)
+        }
+    }
+}
+
+private class FirFakeArgumentForCallableReference(
+    val index: Int
+) : FirExpression() {
+    override val source: FirSourceElement?
+        get() = null
+
+    override val typeRef: FirTypeRef
+        get() = error("should not be called")
+
+    override val annotations: List<FirAnnotationCall>
+        get() = error("should not be called")
+
+    override fun replaceTypeRef(newTypeRef: FirTypeRef) {
+        error("should not be called")
+    }
+
+    override fun <D> transformAnnotations(transformer: FirTransformer<D>, data: D): FirNamedArgumentExpression {
+        error("should not be called")
+    }
+
+    override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
+        error("should not be called")
+    }
+
+    override fun <D> transformChildren(transformer: FirTransformer<D>, data: D): FirElement {
+        error("should not be called")
+    }
+}
+
+fun ConeKotlinType.isKCallableType(): Boolean {
+    return this.classId == StandardClassIds.KCallable
+}
+
+private fun createKPropertyType(
+    propertyOrField: FirVariable<*>,
+    receiverType: ConeKotlinType?,
+    returnTypeRef: FirResolvedTypeRef
+): ConeKotlinType {
+    val propertyType = returnTypeRef.type
+    return org.jetbrains.kotlin.fir.resolve.createKPropertyType(
+        receiverType, propertyType, isMutable = propertyOrField.isVar
+    )
+}

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/ResolutionDiagnostic.kt

@@ -58,3 +58,5 @@ object HiddenCandidate : ResolutionDiagnostic(CandidateApplicability.HIDDEN)
 object ResolvedWithLowPriority : ResolutionDiagnostic(CandidateApplicability.RESOLVED_LOW_PRIORITY)
 
 object InapplicableWrongReceiver : ResolutionDiagnostic(CandidateApplicability.INAPPLICABLE_WRONG_RECEIVER)
+
+object LowerPriorityToPreserveCompatibilityDiagnostic : ResolutionDiagnostic(CandidateApplicability.RESOLVED_NEED_PRESERVE_COMPATIBILITY)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/ResolutionStages.kt

@@ -7,8 +7,6 @@ package org.jetbrains.kotlin.fir.resolve.calls
 
 import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.declarations.*
-import org.jetbrains.kotlin.fir.diagnostics.ConeSimpleDiagnostic
-import org.jetbrains.kotlin.fir.diagnostics.DiagnosticKind
 import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
 import org.jetbrains.kotlin.fir.expressions.FirResolvedQualifier
@@ -24,8 +22,6 @@ import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.resolve.calls.inference.ConstraintSystemOperation
-import org.jetbrains.kotlin.resolve.calls.inference.model.SimpleConstraintSystemConstraintPosition
 import org.jetbrains.kotlin.resolve.calls.tasks.ExplicitReceiverKind
 import org.jetbrains.kotlin.resolve.calls.tasks.ExplicitReceiverKind.*
 
@@ -196,165 +192,6 @@ internal object EagerResolveOfCallableReferences : CheckerStage() {
     }
 }
 
-internal object CheckCallableReferenceExpectedType : CheckerStage() {
-    override suspend fun check(candidate: Candidate, callInfo: CallInfo, sink: CheckerSink, context: ResolutionContext) {
-        val outerCsBuilder = callInfo.outerCSBuilder ?: return
-        val expectedType = callInfo.expectedType
-        if (candidate.symbol !is FirCallableSymbol<*>) return
-
-        val resultingReceiverType = when (callInfo.lhs) {
-            is DoubleColonLHS.Type -> callInfo.lhs.type.takeIf { callInfo.explicitReceiver !is FirResolvedQualifier }
-            else -> null
-        }
-
-        val fir: FirCallableDeclaration<*> = candidate.symbol.fir
-
-        val returnTypeRef = context.bodyResolveComponents.returnTypeCalculator.tryCalculateReturnType(fir)
-        // If the expected type is a suspend function type and the current argument of interest is a function reference, we need to do
-        // "suspend conversion." Here, during resolution, we bypass constraint system by making resulting type be KSuspendFunction.
-        // Then, during conversion, we need to create an adapter function and replace the function reference created here with an adapted
-        // callable reference.
-        // TODO: should refer to LanguageVersionSettings.SuspendConversion
-        val requireSuspendConversion = expectedType?.isSuspendFunctionType(callInfo.session) == true
-        val resultingType: ConeKotlinType = when (fir) {
-            is FirFunction -> callInfo.session.createAdaptedKFunctionType(
-                fir,
-                resultingReceiverType, returnTypeRef, expectedParameterTypes = expectedType?.typeArguments,
-                isSuspend = (fir as? FirSimpleFunction)?.isSuspend == true || requireSuspendConversion,
-                expectedReturnType = extractInputOutputTypesFromCallableReferenceExpectedType(expectedType, callInfo.session)?.outputType
-            )
-            is FirVariable<*> -> createKPropertyType(fir, resultingReceiverType, returnTypeRef)
-            else -> ConeKotlinErrorType(ConeSimpleDiagnostic("Unknown callable kind: ${fir::class}", DiagnosticKind.UnknownCallableKind))
-        }.let(candidate.substitutor::substituteOrSelf)
-        candidate.usesSuspendConversion = requireSuspendConversion
-        candidate.resultingTypeForCallableReference = resultingType
-        candidate.outerConstraintBuilderEffect = fun ConstraintSystemOperation.() {
-            addOtherSystem(candidate.system.asReadOnlyStorage())
-
-            val position = SimpleConstraintSystemConstraintPosition //TODO
-
-            if (expectedType != null) {
-                addSubtypeConstraint(resultingType, expectedType, position)
-            }
-
-            val declarationReceiverType: ConeKotlinType? =
-                (fir as? FirCallableMemberDeclaration<*>)?.receiverTypeRef?.coneType
-                    ?.let(candidate.substitutor::substituteOrSelf)
-
-            if (resultingReceiverType != null && declarationReceiverType != null) {
-                addSubtypeConstraint(resultingReceiverType, declarationReceiverType, position)
-            }
-        }
-
-        var isApplicable = true
-
-        outerCsBuilder.runTransaction {
-            candidate.outerConstraintBuilderEffect!!(this)
-
-            isApplicable = !hasContradiction
-
-            false
-        }
-
-        if (!isApplicable) {
-            sink.yieldDiagnostic(InapplicableCandidate)
-        }
-    }
-}
-
-private fun createKPropertyType(
-    propertyOrField: FirVariable<*>,
-    receiverType: ConeKotlinType?,
-    returnTypeRef: FirResolvedTypeRef
-): ConeKotlinType {
-    val propertyType = returnTypeRef.type
-    return createKPropertyType(
-        receiverType, propertyType, isMutable = propertyOrField.isVar
-    )
-}
-
-private fun FirSession.createAdaptedKFunctionType(
-    function: FirFunction<*>,
-    receiverType: ConeKotlinType?,
-    returnTypeRef: FirResolvedTypeRef,
-    expectedParameterTypes: Array<out ConeTypeProjection>?,
-    isSuspend: Boolean,
-    expectedReturnType: ConeKotlinType?
-): ConeKotlinType {
-    // The similar adaptations: defaults and coercion-to-unit happen at org.jetbrains.kotlin.resolve.calls.components.CallableReferencesCandidateFactory.getCallableReferenceAdaptation
-    val parameterTypes = mutableListOf<ConeKotlinType>()
-    val shift = if (receiverType != null) 1 else 0
-    val expectedParameterNumber =
-        if (expectedParameterTypes == null) null
-        // Drop the last one: return type, and the first one: receiver type, if needed
-        else expectedParameterTypes.size - 1 - shift
-
-    fun ConeKotlinType?.isPotentiallyArray(): Boolean =
-        this != null && (this.arrayElementType() != null || this is ConeTypeVariableType)
-
-    var lastVarargParameter: FirValueParameter? = null
-    for ((index, valueParameter) in function.valueParameters.withIndex()) {
-        // Update the last vararg parameter in preparation for adaptation.
-        if (valueParameter.isVararg) {
-            lastVarargParameter = valueParameter
-        }
-        // Pack value parameters until the expected parameter number is met.
-        if (expectedParameterNumber == null || index < expectedParameterNumber) {
-            // But, if the value parameter is vararg, make sure it matches with the expected parameter type.
-            if (expectedParameterTypes != null && valueParameter.isVararg) {
-                val expectedParameterType = (expectedParameterTypes[index + shift] as? ConeKotlinTypeProjection)?.type
-                if (!expectedParameterType.isPotentiallyArray()) {
-                    // Expect an element. Will spread vararg parameter later.
-                    continue
-                }
-            }
-            parameterTypes += valueParameter.returnTypeRef.coneType
-            continue
-        }
-        // After expected parameters are fulfilled, a value parameter which doesn't have a default value or isn't vararg should be added to
-        // the resulting type (so that it can reject incompatible function reference). In either case, we can't assume no actual arguments
-        // are given.
-        if (valueParameter.defaultValue == null && !valueParameter.isVararg) {
-            parameterTypes += valueParameter.returnTypeRef.coneType
-        }
-    }
-
-    // If a function with vararg is passed to a place where a spread of elements is expected, we can adapt the function reference to
-    // literally spread such vararg argument. E.g., foo(vararg xs: Char): String => bar(::foo) where bar(f: (Char, Char) -> String)
-    if (expectedParameterNumber != null &&
-        expectedParameterTypes != null &&
-        parameterTypes.size < expectedParameterNumber &&
-        lastVarargParameter != null
-    ) {
-        val varargArrayType = lastVarargParameter.returnTypeRef.coneType
-        val varargElementType = varargArrayType.varargElementType()
-        val expectedParameterType = (expectedParameterTypes[parameterTypes.size + shift] as? ConeKotlinTypeProjection)?.type
-        // Expect an array or potentially array (i.e., type variable). Pass vararg parameter as-is.
-        if (expectedParameterType.isPotentiallyArray()) {
-            parameterTypes += varargArrayType
-        } else {
-            // Expect an element. Spread vararg parameter.
-            while (parameterTypes.size < expectedParameterNumber) {
-                parameterTypes += varargElementType
-            }
-        }
-    }
-
-    val returnType =
-        if (expectedReturnType != null && typeContext.run { expectedReturnType.isUnit() })
-            expectedReturnType
-        else
-            returnTypeRef.type
-
-    return createFunctionalType(
-        parameterTypes,
-        receiverType = receiverType,
-        rawReturnType = returnType,
-        isKFunctionType = true,
-        isSuspend = isSuspend
-    )
-}
-
 internal object DiscriminateSynthetics : CheckerStage() {
     override suspend fun check(candidate: Candidate, callInfo: CallInfo, sink: CheckerSink, context: ResolutionContext) {
         if (candidate.symbol is SyntheticSymbol) {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/diagnostics/FirDiagnostics.kt

@@ -5,7 +5,9 @@
 
 package org.jetbrains.kotlin.fir.resolve.diagnostics
 
+import org.jetbrains.kotlin.fir.declarations.FirCallableDeclaration
 import org.jetbrains.kotlin.fir.diagnostics.ConeDiagnostic
+import org.jetbrains.kotlin.fir.render
 import org.jetbrains.kotlin.fir.resolve.calls.Candidate
 import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
@@ -80,6 +82,10 @@ class ConeInstanceAccessBeforeSuperCall(val target: String) : ConeDiagnostic() {
     override val reason: String get() = "Cannot access ''${target}'' before superclass constructor has been called"
 }
 
+class ConeUnsupportedCallableReferenceTarget(val fir: FirCallableDeclaration<*>) : ConeDiagnostic() {
+    override val reason: String get() = "Unsupported declaration for callable reference: ${fir.render()}"
+}
+
 private fun describeSymbol(symbol: AbstractFirBasedSymbol<*>): String {
     return when (symbol) {
         is FirClassLikeSymbol<*> -> symbol.classId.asString()

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/ArrayUtils.kt

@@ -7,6 +7,10 @@ package org.jetbrains.kotlin.fir.types
 
 import org.jetbrains.kotlin.fir.symbols.StandardClassIds
 
+fun ConeKotlinType.createOutArrayType(nullable: Boolean = false): ConeKotlinType {
+    return ConeKotlinTypeProjectionOut(this).createArrayOf(nullable)
+}
+
 fun ConeTypeProjection.createArrayOf(nullable: Boolean = false): ConeKotlinType {
     if (this is ConeKotlinTypeProjection) {
         val type = type.lowerBoundIfFlexible()

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/components/SuspendConversionStrategy.kt

@@ -0,0 +1,10 @@
+/*
+ * Copyright 2010-2020 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.resolve.calls.components
+
+enum class SuspendConversionStrategy {
+    SUSPEND_CONVERSION, NO_CONVERSION
+}

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/CallableReferenceResolution.kt

@@ -88,10 +88,6 @@ class CallableReferenceAdaptation(
     val suspendConversionStrategy: SuspendConversionStrategy
 )
 
-enum class SuspendConversionStrategy {
-    SUSPEND_CONVERSION, NO_CONVERSION
-}
-
 /**
  * cases: class A {}, class B { companion object }, object C, enum class D { E }
  * A::foo <-> Type

compiler/testData/codegen/box/callableReference/equality/varargAsArrayWithDefaults.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // FILE: test.kt
 
 fun checkNotEqual(x: Any, y: Any) {

compiler/testData/diagnostics/tests/callableReference/resolve/overloads.fir.kt

@@ -26,5 +26,5 @@ fun test() {
 
     <!UNRESOLVED_REFERENCE!>B::bas<!>
 
-    ::fas
-}
+    <!UNRESOLVED_REFERENCE!>::fas<!>
+}

compiler/testData/diagnostics/tests/varargs/varargViewedAsArray.fir.kt

@@ -23,7 +23,7 @@ fun test() {
     usePrimitiveIntArray(::intVararg)
     <!INAPPLICABLE_CANDIDATE!>useIntArray<!>(<!UNRESOLVED_REFERENCE!>::intVararg<!>)
     <!INAPPLICABLE_CANDIDATE!>useMixedStringArgs1<!>(<!UNRESOLVED_REFERENCE!>::stringVararg<!>)
-    useMixedStringArgs2(::stringVararg)
+    <!INAPPLICABLE_CANDIDATE!>useMixedStringArgs2<!>(<!UNRESOLVED_REFERENCE!>::stringVararg<!>)
     <!INAPPLICABLE_CANDIDATE!>useMixedStringArgs3<!>(<!UNRESOLVED_REFERENCE!>::stringVararg<!>)
-    useTwoStringArrays(::stringVararg)
+    <!INAPPLICABLE_CANDIDATE!>useTwoStringArrays<!>(<!UNRESOLVED_REFERENCE!>::stringVararg<!>)
 }

compiler/testData/ir/irText/expressions/callableReferences/caoWithAdaptationForSam.fir.txt

@@ -107,26 +107,26 @@ FILE fqName:<root> fileName:/caoWithAdaptationForSam.kt
       BLOCK type=kotlin.Unit origin=null
         VAR IR_TEMPORARY_VARIABLE name:tmp_0 type:<root>.A [val]
           GET_OBJECT 'CLASS OBJECT name:A modality:FINAL visibility:public superTypes:[kotlin.Any]' type=<root>.A
-        VAR IR_TEMPORARY_VARIABLE name:tmp_1 type:kotlin.reflect.KFunction0<kotlin.Int> [val]
-          FUNCTION_REFERENCE 'public final fun withVararg (vararg xs: kotlin.Int): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null reflectionTarget=<same>
+        VAR IR_TEMPORARY_VARIABLE name:tmp_1 type:kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> [val]
+          FUNCTION_REFERENCE 'public final fun withVararg (vararg xs: kotlin.Int): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null reflectionTarget=<same>
         ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): /set>#' type=kotlin.Unit
-          GET_VAR 'val tmp_1: kotlin.reflect.KFunction0<kotlin.Int> [val] declared in <root>.test1' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null
+          GET_VAR 'val tmp_1: kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> [val] declared in <root>.test1' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null
           CALL 'public final fun plus (other: kotlin.Int): kotlin.Int [operator] declared in kotlin.Int' type=kotlin.Int origin=null
             $this: ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): /get>#' type=kotlin.Int
-              GET_VAR 'val tmp_1: kotlin.reflect.KFunction0<kotlin.Int> [val] declared in <root>.test1' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null
+              GET_VAR 'val tmp_1: kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> [val] declared in <root>.test1' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null
             other: CONST Int type=kotlin.Int value=1
   FUN name:test2 visibility:public modality:FINAL <> () returnType:kotlin.Unit
     BLOCK_BODY
       BLOCK type=kotlin.Unit origin=null
         VAR IR_TEMPORARY_VARIABLE name:tmp_2 type:<root>.B [val]
           GET_OBJECT 'CLASS OBJECT name:B modality:FINAL visibility:public superTypes:[kotlin.Any]' type=<root>.B
-        VAR IR_TEMPORARY_VARIABLE name:tmp_3 type:kotlin.reflect.KFunction0<kotlin.Int> [val]
-          FUNCTION_REFERENCE 'public final fun withVararg (vararg xs: kotlin.Int): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null reflectionTarget=<same>
+        VAR IR_TEMPORARY_VARIABLE name:tmp_3 type:kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> [val]
+          FUNCTION_REFERENCE 'public final fun withVararg (vararg xs: kotlin.Int): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null reflectionTarget=<same>
         ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): /set>#' type=kotlin.Unit
-          GET_VAR 'val tmp_3: kotlin.reflect.KFunction0<kotlin.Int> [val] declared in <root>.test2' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null
+          GET_VAR 'val tmp_3: kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> [val] declared in <root>.test2' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null
           CALL 'public final fun plus (other: kotlin.Int): kotlin.Int [operator] declared in kotlin.Int' type=kotlin.Int origin=null
             $this: ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): /get>#' type=kotlin.Int
-              GET_VAR 'val tmp_3: kotlin.reflect.KFunction0<kotlin.Int> [val] declared in <root>.test2' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null
+              GET_VAR 'val tmp_3: kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> [val] declared in <root>.test2' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null
             other: CONST Int type=kotlin.Int value=1
   FUN name:test3 visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Int, kotlin.Unit>) returnType:kotlin.Unit
     VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Int, kotlin.Unit>

compiler/testData/ir/irText/expressions/callableReferences/funWithDefaultParametersAsKCallableStar.fir.txt

@@ -1,73 +0,0 @@
-FILE fqName:<root> fileName:/funWithDefaultParametersAsKCallableStar.kt
-  FUN name:defaultsOnly visibility:public modality:FINAL <> (x:kotlin.String) returnType:kotlin.Int
-    VALUE_PARAMETER name:x index:0 type:kotlin.String
-      EXPRESSION_BODY
-        CONST String type=kotlin.String value=""
-    BLOCK_BODY
-      RETURN type=kotlin.Nothing from='public final fun defaultsOnly (x: kotlin.String): kotlin.Int declared in <root>'
-        CONST Int type=kotlin.Int value=1
-  FUN name:regularAndDefaults visibility:public modality:FINAL <> (x1:kotlin.String, x2:kotlin.String) returnType:kotlin.Int
-    VALUE_PARAMETER name:x1 index:0 type:kotlin.String
-    VALUE_PARAMETER name:x2 index:1 type:kotlin.String
-      EXPRESSION_BODY
-        CONST String type=kotlin.String value=""
-    BLOCK_BODY
-      RETURN type=kotlin.Nothing from='public final fun regularAndDefaults (x1: kotlin.String, x2: kotlin.String): kotlin.Int declared in <root>'
-        CONST Int type=kotlin.Int value=1
-  FUN name:varargs visibility:public modality:FINAL <> (xs:kotlin.Array<out kotlin.String>) returnType:kotlin.Int
-    VALUE_PARAMETER name:xs index:0 type:kotlin.Array<out kotlin.String> varargElementType:kotlin.String [vararg]
-    BLOCK_BODY
-      RETURN type=kotlin.Nothing from='public final fun varargs (vararg xs: kotlin.String): kotlin.Int declared in <root>'
-        CONST Int type=kotlin.Int value=1
-  CLASS CLASS name:C modality:FINAL visibility:public superTypes:[kotlin.Any]
-    $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.C
-    CONSTRUCTOR visibility:public <> (x:kotlin.String) returnType:<root>.C [primary]
-      VALUE_PARAMETER name:x index:0 type:kotlin.String
-        EXPRESSION_BODY
-          CONST String type=kotlin.String value=""
-      BLOCK_BODY
-        DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
-        INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:C modality:FINAL visibility:public superTypes:[kotlin.Any]'
-    PROPERTY name:x visibility:public modality:FINAL [val]
-      FIELD PROPERTY_BACKING_FIELD name:x type:kotlin.String visibility:private [final]
-        EXPRESSION_BODY
-          GET_VAR 'x: kotlin.String declared in <root>.C.<init>' type=kotlin.String origin=INITIALIZE_PROPERTY_FROM_PARAMETER
-      FUN DEFAULT_PROPERTY_ACCESSOR name:<get-x> visibility:public modality:FINAL <> ($this:<root>.C) returnType:kotlin.String
-        correspondingProperty: PROPERTY name:x visibility:public modality:FINAL [val]
-        $this: VALUE_PARAMETER name:<this> type:<root>.C
-        BLOCK_BODY
-          RETURN type=kotlin.Nothing from='public final fun <get-x> (): kotlin.String declared in <root>.C'
-            GET_FIELD 'FIELD PROPERTY_BACKING_FIELD name:x type:kotlin.String visibility:private [final]' type=kotlin.String origin=null
-              receiver: GET_VAR '<this>: <root>.C declared in <root>.C.<get-x>' type=<root>.C origin=null
-    FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [fake_override,operator]
-      overridden:
-        public open fun equals (other: kotlin.Any?): kotlin.Boolean [operator] declared in kotlin.Any
-      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
-      VALUE_PARAMETER name:other index:0 type:kotlin.Any?
-    FUN FAKE_OVERRIDE name:hashCode visibility:public modality:OPEN <> ($this:kotlin.Any) returnType:kotlin.Int [fake_override]
-      overridden:
-        public open fun hashCode (): kotlin.Int declared in kotlin.Any
-      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
-    FUN FAKE_OVERRIDE name:toString visibility:public modality:OPEN <> ($this:kotlin.Any) returnType:kotlin.String [fake_override]
-      overridden:
-        public open fun toString (): kotlin.String declared in kotlin.Any
-      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
-  FUN name:useKCallableStar visibility:public modality:FINAL <> (fn:kotlin.reflect.KCallable<*>) returnType:kotlin.Unit
-    VALUE_PARAMETER name:fn index:0 type:kotlin.reflect.KCallable<*>
-    BLOCK_BODY
-  FUN name:testDefaultsOnlyStar visibility:public modality:FINAL <> () returnType:kotlin.Unit
-    BLOCK_BODY
-      CALL 'public final fun useKCallableStar (fn: kotlin.reflect.KCallable<*>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
-        fn: FUNCTION_REFERENCE 'public final fun defaultsOnly (x: kotlin.String): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null reflectionTarget=<same>
-  FUN name:testRegularAndDefaultsStar visibility:public modality:FINAL <> () returnType:kotlin.Unit
-    BLOCK_BODY
-      CALL 'public final fun useKCallableStar (fn: kotlin.reflect.KCallable<*>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
-        fn: FUNCTION_REFERENCE 'public final fun regularAndDefaults (x1: kotlin.String, x2: kotlin.String): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.String, kotlin.Int> origin=null reflectionTarget=<same>
-  FUN name:testVarargsStar visibility:public modality:FINAL <> () returnType:kotlin.Unit
-    BLOCK_BODY
-      CALL 'public final fun useKCallableStar (fn: kotlin.reflect.KCallable<*>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
-        fn: FUNCTION_REFERENCE 'public final fun varargs (vararg xs: kotlin.String): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction0<kotlin.Int> origin=null reflectionTarget=<same>
-  FUN name:testCtorStar visibility:public modality:FINAL <> () returnType:kotlin.Unit
-    BLOCK_BODY
-      CALL 'public final fun useKCallableStar (fn: kotlin.reflect.KCallable<*>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
-        fn: FUNCTION_REFERENCE 'public constructor <init> (x: kotlin.String) [primary] declared in <root>.C' type=kotlin.reflect.KFunction0<<root>.C> origin=null reflectionTarget=<same>

compiler/testData/ir/irText/expressions/callableReferences/funWithDefaultParametersAsKCallableStar.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // WITH_REFLECT
 import kotlin.reflect.KCallable