PSI2IR: Generate adapted callable references

Callable reference is "adapted" if it requires some adaptation to an
expected function type - e.g., when a reference to
```
  fun foo(vararg xs: Int): Int
```
is used where `(Int, Int, Int) -> Int` is expected.

For such callable references we generate the following IR (in
pseudo-Kotlin):
```
  {
    fun foo'(p0: Int, p1: Int, p2: Int): Int {
      return [| foo(p0, p1, p2) |]
    }
    ::foo'
  }
```

where `[| foo(p0, p1, p2) |]` is calling function `foo` with arguments
`p0`, `p1`, and `p2`, as they were mapped by callable reference
resolution.

compiler/fir/fir2ir/tests/org/jetbrains/kotlin/fir/Fir2IrTextTestGenerated.java

@@ -802,6 +802,16 @@ public class Fir2IrTextTestGenerated extends AbstractFir2IrTextTest {
             runTest("compiler/testData/ir/irText/expressions/callableReferenceTypeArguments.kt");
         }
 
+        @TestMetadata("callableReferenceWithArgumentsConversion.kt")
+        public void testCallableReferenceWithArgumentsConversion() throws Exception {
+            runTest("compiler/testData/ir/irText/expressions/callableReferenceWithArgumentsConversion.kt");
+        }
+
+        @TestMetadata("callableReferenceWithVarargViewedAsArray.kt")
+        public void testCallableReferenceWithVarargViewedAsArray() throws Exception {
+            runTest("compiler/testData/ir/irText/expressions/callableReferenceWithVarargViewedAsArray.kt");
+        }
+
         @TestMetadata("calls.kt")
         public void testCalls() throws Exception {
             runTest("compiler/testData/ir/irText/expressions/calls.kt");

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tower/NewCallArguments.kt

@@ -193,6 +193,18 @@ class FakePositionalValueArgumentForCallableReferenceImpl(
     override fun isExternal(): Boolean = false
 }
 
+class FakeImplicitSpreadValueArgumentForCallableReferenceImpl(
+    private val callElement: KtElement,
+    override val expression: ValueArgument
+) : FakeImplicitSpreadValueArgumentForCallableReference {
+    override fun getArgumentExpression(): KtExpression? = null
+    override fun getArgumentName(): ValueArgumentName? = null
+    override fun isNamed(): Boolean = false
+    override fun asElement(): KtElement = callElement
+    override fun getSpreadElement(): LeafPsiElement? = null // TODO callElement?
+    override fun isExternal(): Boolean = false
+}
+
 class EmptyLabeledReturn(
     val returnExpression: KtReturnExpression,
     builtIns: KotlinBuiltIns

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tower/ResolvedAtomCompleter.kt

@@ -7,7 +7,10 @@ package org.jetbrains.kotlin.resolve.calls.tower
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.builtins.createFunctionType
-import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.CallableDescriptor
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
+import org.jetbrains.kotlin.descriptors.ModuleDescriptor
+import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.descriptors.impl.FunctionDescriptorImpl
 import org.jetbrains.kotlin.descriptors.impl.ReceiverParameterDescriptorImpl
 import org.jetbrains.kotlin.psi.KtElement
@@ -377,7 +380,11 @@ class ResolvedAtomCompleter(
                     is ResolvedCallArgument.SimpleArgument -> {
                         val valueArgument = makeFakeValueArgument(resolvedCallArgument.callArgument, callElement)
                         if (valueParameter.isVararg)
-                            VarargValueArgument(listOf(valueArgument))
+                            VarargValueArgument(
+                                listOf(
+                                    FakeImplicitSpreadValueArgumentForCallableReferenceImpl(callElement, valueArgument)
+                                )
+                            )
                         else
                             ExpressionValueArgument(valueArgument)
                     }

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

@@ -134,8 +134,11 @@ val IrType.isBoxedArray: Boolean
 fun IrType.getArrayElementType(irBuiltIns: IrBuiltIns): IrType =
     if (isBoxedArray)
         ((this as IrSimpleType).arguments.single() as IrTypeProjection).type
-    else
+    else {
-        irBuiltIns.primitiveArrayElementTypes.getValue(this.classOrNull!!)
+        val classifier = this.classOrNull!!
+        irBuiltIns.primitiveArrayElementTypes[classifier]
+            ?: throw AssertionError("Primitive array expected: $classifier")
+    }
 
 val IrStatementOrigin?.isLambda: Boolean
     get() = this == IrStatementOrigin.LAMBDA || this == IrStatementOrigin.ANONYMOUS_FUNCTION

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/ReflectionReferencesGenerator.kt

@@ -16,19 +16,30 @@
 
 package org.jetbrains.kotlin.psi2ir.generators
 
+import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
+import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
+import org.jetbrains.kotlin.ir.declarations.MetadataSource
+import org.jetbrains.kotlin.ir.declarations.impl.IrFunctionImpl
+import org.jetbrains.kotlin.ir.declarations.impl.IrValueParameterImpl
+import org.jetbrains.kotlin.ir.descriptors.WrappedSimpleFunctionDescriptor
+import org.jetbrains.kotlin.ir.descriptors.WrappedValueParameterDescriptor
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.*
+import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
 import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.IrVariableSymbol
 import org.jetbrains.kotlin.ir.util.referenceClassifier
 import org.jetbrains.kotlin.ir.util.referenceFunction
-import org.jetbrains.kotlin.psi.KtCallableReferenceExpression
+import org.jetbrains.kotlin.ir.util.withScope
-import org.jetbrains.kotlin.psi.KtClassLiteralExpression
+import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.psi.KtElement
+import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.endOffset
 import org.jetbrains.kotlin.psi.psiUtil.startOffsetSkippingComments
+import org.jetbrains.kotlin.psi2ir.intermediate.CallBuilder
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.calls.model.*
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.expressions.DoubleColonLHS
 
@@ -61,6 +72,15 @@ class ReflectionReferencesGenerator(statementGenerator: StatementGenerator) : St
 
         val callBuilder = unwrapCallableDescriptorAndTypeArguments(resolvedCall, context.extensions.samConversion)
 
+        if (resolvedCall.valueArguments.isNotEmpty()) {
+            val adaptedCallableReference = generateAdaptedCallableReference(ktCallableReference, callBuilder)
+            if (adaptedCallableReference.hasResultAdaptation ||
+                !isTrivialArgumentAdaptation(adaptedCallableReference.irAdapteeCall)
+            ) {
+                return adaptedCallableReference.irReferenceExpression
+            }
+        }
+
         return statementGenerator.generateCallReceiver(
             ktCallableReference,
             resolvedDescriptor,
@@ -79,6 +99,252 @@ class ReflectionReferencesGenerator(statementGenerator: StatementGenerator) : St
         }
     }
 
+    private fun isTrivialArgumentAdaptation(irAdapteeCall: IrFunctionAccessExpression): Boolean {
+        for (i in 0 until irAdapteeCall.valueArgumentsCount) {
+            val irValueArgument = irAdapteeCall.getValueArgument(i) ?: return false
+            if (irValueArgument is IrVararg) {
+                val irVarargElements = irValueArgument.elements
+                if (irVarargElements.size != 1 || irVarargElements[0] !is IrSpreadElement) return false
+            }
+        }
+        return true
+    }
+
+    private class AdaptedCallableReference(
+        val irReferenceExpression: IrExpression,
+        val irAdapteeCall: IrFunctionAccessExpression,
+        val hasResultAdaptation: Boolean
+    )
+
+    private fun generateAdaptedCallableReference(
+        ktCallableReference: KtCallableReferenceExpression,
+        callBuilder: CallBuilder
+    ): AdaptedCallableReference {
+        val adapteeDescriptor = callBuilder.descriptor
+        if (adapteeDescriptor !is FunctionDescriptor) {
+            throw AssertionError("Function descriptor expected in adapted callable reference: $adapteeDescriptor")
+        }
+
+        val startOffset = ktCallableReference.startOffsetSkippingComments
+        val endOffset = ktCallableReference.endOffset
+
+        val adapteeSymbol = context.symbolTable.referenceFunction(adapteeDescriptor.original)
+
+        val ktFunctionalType = getTypeInferredByFrontendOrFail(ktCallableReference)
+        val irFunctionalType = ktFunctionalType.toIrType()
+
+        val ktFunctionalTypeArguments = ktFunctionalType.arguments
+        val ktExpectedReturnType = ktFunctionalTypeArguments.last().type
+        val ktExpectedParameterTypes = ktFunctionalTypeArguments.take(ktFunctionalTypeArguments.size - 1).map { it.type }
+
+        val irAdapterFun = createAdapterFun(startOffset, endOffset, adapteeDescriptor, ktExpectedParameterTypes, ktExpectedReturnType)
+        val (irCall, irAdapteeCallInner) =
+            createAdapteeCall(startOffset, endOffset, ktCallableReference, adapteeSymbol, callBuilder, irAdapterFun)
+
+        irAdapterFun.body = IrBlockBodyImpl(startOffset, endOffset).apply {
+            if (KotlinBuiltIns.isUnit(ktExpectedReturnType))
+                statements.add(irCall)
+            else
+                statements.add(IrReturnImpl(startOffset, endOffset, context.irBuiltIns.nothingType, irAdapterFun.symbol, irCall))
+        }
+
+        val irBlock = IrBlockImpl(startOffset, endOffset, irFunctionalType).apply {
+            statements.add(irAdapterFun)
+            statements.add(
+                IrFunctionReferenceImpl(
+                    startOffset, endOffset,
+                    irFunctionalType,
+                    irAdapterFun.symbol,
+                    0,
+                    irAdapterFun.valueParameters.size
+                )
+            )
+        }
+
+        return AdaptedCallableReference(
+            irBlock, irAdapteeCallInner,
+            KotlinBuiltIns.isUnit(ktExpectedReturnType) && !KotlinBuiltIns.isUnit(adapteeDescriptor.returnType!!)
+        )
+    }
+
+    private fun createAdapteeCall(
+        startOffset: Int,
+        endOffset: Int,
+        ktCallableReference: KtCallableReferenceExpression,
+        adapteeSymbol: IrFunctionSymbol,
+        callBuilder: CallBuilder,
+        irAdapterFun: IrSimpleFunction
+    ): Pair<IrExpression, IrFunctionAccessExpression> {
+        val resolvedCall = callBuilder.original
+        val resolvedDescriptor = resolvedCall.resultingDescriptor
+
+        var irAdapteeCall: IrFunctionAccessExpression? = null
+        val irCall = statementGenerator.generateCallReceiver(
+            ktCallableReference,
+            resolvedDescriptor,
+            resolvedCall.dispatchReceiver, resolvedCall.extensionReceiver,
+            isSafe = false
+        ).call { dispatchReceiverValue, extensionReceiverValue ->
+            val irType = resolvedDescriptor.returnType!!.toIrType()
+
+            val irAdapteeCallInner =
+                if (resolvedDescriptor is ConstructorDescriptor)
+                    IrConstructorCallImpl.fromSymbolDescriptor(
+                        startOffset, endOffset, irType,
+                        adapteeSymbol as IrConstructorSymbol
+                    )
+                else
+                    IrCallImpl(
+                        startOffset, endOffset, irType,
+                        adapteeSymbol,
+                        origin = null, superQualifierSymbol = null
+                    )
+
+            context.callToSubstitutedDescriptorMap[irAdapteeCallInner] = resolvedDescriptor
+
+            irAdapteeCallInner.dispatchReceiver = dispatchReceiverValue?.load()
+            irAdapteeCallInner.extensionReceiver = extensionReceiverValue?.load()
+
+            irAdapteeCallInner.putTypeArguments(callBuilder.typeArguments) { it.toIrType() }
+
+            putAdaptedValueArguments(startOffset, endOffset, irAdapteeCallInner, irAdapterFun, resolvedCall)
+
+            irAdapteeCall = irAdapteeCallInner
+
+            irAdapteeCallInner
+        }
+
+        return Pair(irCall, irAdapteeCall!!)
+    }
+
+    private fun putAdaptedValueArguments(
+        startOffset: Int,
+        endOffset: Int,
+        irAdapteeCall: IrFunctionAccessExpression,
+        irAdapterFun: IrSimpleFunction,
+        resolvedCall: ResolvedCall<*>
+    ) {
+        val adaptedArguments = resolvedCall.valueArguments
+        if (adaptedArguments.isEmpty()) {
+            throw AssertionError("Callable reference with adapted arguments expected: ${resolvedCall.call.callElement.text}")
+        }
+
+        for ((valueParameter, valueArgument) in adaptedArguments) {
+            irAdapteeCall.putValueArgument(
+                valueParameter.index,
+                adaptResolvedValueArgument(startOffset, endOffset, valueArgument, irAdapterFun, valueParameter)
+            )
+        }
+    }
+
+    private fun adaptResolvedValueArgument(
+        startOffset: Int,
+        endOffset: Int,
+        resolvedValueArgument: ResolvedValueArgument,
+        irAdapterFun: IrSimpleFunction,
+        valueParameter: ValueParameterDescriptor
+    ): IrExpression? =
+        when (resolvedValueArgument) {
+            is DefaultValueArgument ->
+                null
+            is VarargValueArgument ->
+                IrVarargImpl(
+                    startOffset, endOffset,
+                    valueParameter.type.toIrType(), valueParameter.varargElementType!!.toIrType(),
+                    resolvedValueArgument.arguments.map {
+                        adaptValueArgument(startOffset, endOffset, it, irAdapterFun)
+                    }
+                )
+            is ExpressionValueArgument -> {
+                val valueArgument = resolvedValueArgument.valueArgument!!
+
+                adaptValueArgument(startOffset, endOffset, valueArgument, irAdapterFun) as IrExpression
+            }
+            else ->
+                throw AssertionError("Unexpected ResolvedValueArgument: $resolvedValueArgument")
+        }
+
+    private fun adaptValueArgument(
+        startOffset: Int,
+        endOffset: Int,
+        valueArgument: ValueArgument,
+        irAdapterFun: IrSimpleFunction
+    ): IrVarargElement =
+        when (valueArgument) {
+            is FakeImplicitSpreadValueArgumentForCallableReference ->
+                IrSpreadElementImpl(
+                    startOffset, endOffset,
+                    adaptValueArgument(startOffset, endOffset, valueArgument.expression, irAdapterFun) as IrExpression
+                )
+
+            is FakePositionalValueArgumentForCallableReference -> {
+                val irAdapterParameter = irAdapterFun.valueParameters[valueArgument.index]
+                IrGetValueImpl(startOffset, endOffset, irAdapterParameter.type, irAdapterParameter.symbol)
+            }
+
+            else ->
+                throw AssertionError("Unexpected ValueArgument: $valueArgument")
+        }
+
+    private fun createAdapterFun(
+        startOffset: Int,
+        endOffset: Int,
+        adapteeDescriptor: FunctionDescriptor,
+        ktExpectedParameterTypes: List<KotlinType>,
+        ktExpectedReturnType: KotlinType
+    ): IrSimpleFunction {
+        val adapterFunctionDescriptor = WrappedSimpleFunctionDescriptor()
+        val adapterOrigin = IrDeclarationOrigin.DEFINED // TODO special declaration origin for callable reference adapter?
+
+        return context.symbolTable.declareSimpleFunction(
+            startOffset, endOffset, adapterOrigin, adapterFunctionDescriptor
+        ) { irAdapterSymbol ->
+            IrFunctionImpl(
+                startOffset, endOffset, adapterOrigin,
+                irAdapterSymbol,
+                adapteeDescriptor.name,
+                Visibilities.LOCAL,
+                Modality.FINAL,
+                ktExpectedReturnType.toIrType(),
+                isInline = adapteeDescriptor.isInline, // TODO ?
+                isExternal = false,
+                isTailrec = false,
+                isSuspend = adapteeDescriptor.isSuspend, // TODO ?
+                isOperator = adapteeDescriptor.isOperator, // TODO ?
+                isExpect = false,
+                isFakeOverride = false
+            ).also { irAdapterFun ->
+                adapterFunctionDescriptor.bind(irAdapterFun)
+
+                context.symbolTable.withScope(adapterFunctionDescriptor) {
+                    irAdapterFun.metadata = MetadataSource.Function(adapteeDescriptor)
+
+                    irAdapterFun.dispatchReceiverParameter = null
+                    irAdapterFun.extensionReceiverParameter = null
+
+                    ktExpectedParameterTypes.mapIndexedTo(irAdapterFun.valueParameters) { index, ktExpectedParameterType ->
+                        val adapterValueParameterDescriptor = WrappedValueParameterDescriptor()
+                        context.symbolTable.declareValueParameter(
+                            startOffset, endOffset, adapterOrigin, adapterValueParameterDescriptor,
+                            ktExpectedParameterType.toIrType()
+                        ) { irAdapterParameterSymbol ->
+                            IrValueParameterImpl(
+                                startOffset, endOffset, adapterOrigin,
+                                irAdapterParameterSymbol,
+                                Name.identifier("p$index"),
+                                index,
+                                ktExpectedParameterType.toIrType(),
+                                varargElementType = null, isCrossinline = false, isNoinline = false
+                            ).also { irAdapterValueParameter ->
+                                adapterValueParameterDescriptor.bind(irAdapterValueParameter)
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
     fun generateCallableReference(
         ktElement: KtElement,
         type: KotlinType,

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

@@ -377,20 +377,18 @@ class DumpTreeFromSourceLineVisitor(
 
 internal fun IrMemberAccessExpression.getValueParameterNamesForDebug(): List<String> {
     val expectedCount = valueArgumentsCount
-    return if (this is IrDeclarationReference && symbol.isBound) {
+    if (symbol.isBound) {
         val owner = symbol.owner
         if (owner is IrFunction) {
-            (0 until expectedCount).map {
+            return (0 until expectedCount).map {
                 if (it < owner.valueParameters.size)
                     owner.valueParameters[it].name.asString()
                 else
                     "${it + 1}"
             }
-        } else {
-            getPlaceholderParameterNames(expectedCount)
         }
-    } else
+    }
-        getPlaceholderParameterNames(expectedCount)
+    return getPlaceholderParameterNames(expectedCount)
 }
 
 internal fun getPlaceholderParameterNames(expectedCount: Int) =

compiler/psi/src/org/jetbrains/kotlin/psi/ValueArgument.kt

@@ -40,6 +40,10 @@ interface FakePositionalValueArgumentForCallableReference : ValueArgument {
     val index: Int
 }
 
+interface FakeImplicitSpreadValueArgumentForCallableReference : ValueArgument {
+    val expression: ValueArgument
+}
+
 interface LambdaArgument : ValueArgument {
     fun getLambdaExpression(): KtLambdaExpression?
 }

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

@@ -266,7 +266,9 @@ class CallableReferencesCandidateFactory(
          */
         var defaults = 0
         var varargMappingState = VarargMappingState.UNMAPPED
-        val mappedArguments = arrayOfNulls<KotlinType?>(fakeArguments.size)
+        val mappedArguments = linkedMapOf<ValueParameterDescriptor, ResolvedCallArgument>()
+        val mappedVarargElements = linkedMapOf<ValueParameterDescriptor, MutableList<KotlinCallArgument>>()
+        val mappedArgumentTypes = arrayOfNulls<KotlinType?>(fakeArguments.size)
 
         for ((valueParameter, resolvedArgument) in argumentMapping.parameterToCallArgumentMap) {
             for (fakeArgument in resolvedArgument.arguments) {
@@ -283,25 +285,42 @@ class CallableReferencesCandidateFactory(
                     )
                     varargMappingState = newVarargMappingState
                     mappedArgument = varargType
+
+                    when (newVarargMappingState) {
+                        VarargMappingState.MAPPED_WITH_ARRAY -> {
+                            if (valueParameter in mappedArguments.keys) {
+                                throw AssertionError("Vararg parameter already mapped: $valueParameter, fakeArgument: $fakeArgument")
+                            }
+                            mappedArguments[valueParameter] = ResolvedCallArgument.SimpleArgument(fakeArgument)
+                        }
+
+                        VarargMappingState.MAPPED_WITH_PLAIN_ARGS -> {
+                            mappedVarargElements.getOrPut(valueParameter) { ArrayList() }.add(fakeArgument)
+                        }
+                    }
                 } else {
                     mappedArgument = substitutedParameter.type
+                    mappedArguments[valueParameter] = resolvedArgument
                 }
 
-                mappedArguments[index] = mappedArgument
+                mappedArgumentTypes[index] = mappedArgument
             }
             if (resolvedArgument == ResolvedCallArgument.DefaultArgument) defaults++
         }
-        if (mappedArguments.any { it == null }) return null
+        if (mappedArgumentTypes.any { it == null }) return null
+
+        for ((valueParameter, varargElements) in mappedVarargElements) {
+            mappedArguments[valueParameter] = ResolvedCallArgument.VarargArgument(varargElements)
+        }
 
         // lower(Unit!) = Unit
         val returnExpectedType = inputOutputTypes.outputType
 
         val coercion = if (returnExpectedType.isUnit()) CoercionStrategy.COERCION_TO_UNIT else CoercionStrategy.NO_COERCION
 
-
         return CallableReferenceAdaptation(
-            @Suppress("UNCHECKED_CAST") (mappedArguments as Array<KotlinType>),
+            @Suppress("UNCHECKED_CAST") (mappedArgumentTypes as Array<KotlinType>),
-            coercion, defaults, argumentMapping.parameterToCallArgumentMap
+            coercion, defaults, mappedArguments
         )
     }
 

compiler/testData/ir/irText/expressions/callableReferenceWithArgumentsConversion.fir.txt

@@ -0,0 +1,69 @@
+FILE fqName:<root> fileName:/callableReferenceWithArgumentsConversion.kt
+  FUN name:use visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Int, kotlin.String>) returnType:kotlin.String
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Int, kotlin.String>
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun use (fn: kotlin.Function1<kotlin.Int, kotlin.String>): kotlin.String declared in <root>'
+        CALL 'public abstract fun invoke (p1: kotlin.Int): kotlin.String [operator] declared in kotlin.Function1' type=kotlin.String origin=null
+          $this: GET_VAR 'fn: kotlin.Function1<kotlin.Int, kotlin.String> declared in <root>.use' type=kotlin.Function1<kotlin.Int, kotlin.String> origin=null
+          p1: CONST Int type=kotlin.Int value=1
+  FUN name:coerceToUnit 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>
+    BLOCK_BODY
+  FUN name:fnWithDefault visibility:public modality:FINAL <> (a:kotlin.Int, b:kotlin.Int) returnType:kotlin.String
+    VALUE_PARAMETER name:a index:0 type:kotlin.Int
+    VALUE_PARAMETER name:b index:1 type:kotlin.Int
+      EXPRESSION_BODY
+        CONST Int type=kotlin.Int value=42
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun fnWithDefault (a: kotlin.Int, b: kotlin.Int): kotlin.String declared in <root>'
+        CONST String type=kotlin.String value="abc"
+  FUN name:fnWithVarargs visibility:public modality:FINAL <> (xs:kotlin.IntArray) returnType:kotlin.String
+    VALUE_PARAMETER name:xs index:0 type:kotlin.IntArray
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun fnWithVarargs (xs: kotlin.IntArray): kotlin.String declared in <root>'
+        CONST String type=kotlin.String value="abc"
+  CLASS OBJECT name:Host modality:FINAL visibility:public superTypes:[kotlin.Any]
+    $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.Host
+    CONSTRUCTOR visibility:private <> () returnType:<root>.Host [primary]
+      BLOCK_BODY
+        DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
+        INSTANCE_INITIALIZER_CALL classDescriptor='CLASS OBJECT name:Host modality:FINAL visibility:public superTypes:[kotlin.Any]'
+    FUN name:importedObjectMemberWithVarargs visibility:public modality:FINAL <> ($this:<root>.Host, xs:kotlin.IntArray) returnType:kotlin.String
+      $this: VALUE_PARAMETER name:<this> type:<root>.Host
+      VALUE_PARAMETER name:xs index:0 type:kotlin.IntArray
+      BLOCK_BODY
+        RETURN type=kotlin.Nothing from='public final fun importedObjectMemberWithVarargs (xs: kotlin.IntArray): kotlin.String declared in <root>.Host'
+          CONST String type=kotlin.String value="abc"
+    FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($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:testDefault visibility:public modality:FINAL <> () returnType:IrErrorType
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testDefault (): IrErrorType declared in <root>'
+        ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/use]>#' type=IrErrorType
+          FUNCTION_REFERENCE 'public final fun fnWithDefault (a: kotlin.Int, b: kotlin.Int): kotlin.String declared in <root>' type=kotlin.reflect.KFunction2<kotlin.Int, kotlin.Int, kotlin.String> origin=null
+  FUN name:testVararg visibility:public modality:FINAL <> () returnType:IrErrorType
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testVararg (): IrErrorType declared in <root>'
+        ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/use]>#' type=IrErrorType
+          FUNCTION_REFERENCE 'public final fun fnWithVarargs (xs: kotlin.IntArray): kotlin.String declared in <root>' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.String> origin=null
+  FUN name:testCoercionToUnit visibility:public modality:FINAL <> () returnType:IrErrorType
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testCoercionToUnit (): IrErrorType declared in <root>'
+        ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/coerceToUnit]>#' type=IrErrorType
+          FUNCTION_REFERENCE 'public final fun fnWithDefault (a: kotlin.Int, b: kotlin.Int): kotlin.String declared in <root>' type=kotlin.reflect.KFunction2<kotlin.Int, kotlin.Int, kotlin.String> origin=null
+  FUN name:testImportedObjectMember visibility:public modality:FINAL <> () returnType:IrErrorType
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testImportedObjectMember (): IrErrorType declared in <root>'
+        ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/use]>#' type=IrErrorType
+          FUNCTION_REFERENCE 'public final fun importedObjectMemberWithVarargs (xs: kotlin.IntArray): kotlin.String declared in <root>.Host' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.String> origin=null

compiler/testData/ir/irText/expressions/callableReferenceWithArgumentsConversion.kt

@@ -0,0 +1,22 @@
+// !LANGUAGE: +NewInference, +FunctionReferenceWithDefaultValueAsOtherType
+import Host.importedObjectMemberWithVarargs
+
+fun use(fn: (Int) -> String) = fn(1)
+
+fun coerceToUnit(fn: (Int) -> Unit) {}
+
+fun fnWithDefault(a: Int, b: Int = 42) = "abc"
+
+fun fnWithVarargs(vararg xs: Int) = "abc"
+
+object Host {
+    fun importedObjectMemberWithVarargs(vararg xs: Int) = "abc"
+}
+
+fun testDefault() = use(::fnWithDefault)
+
+fun testVararg() = use(::fnWithVarargs)
+
+fun testCoercionToUnit() = coerceToUnit(::fnWithDefault)
+
+fun testImportedObjectMember() = use(::importedObjectMemberWithVarargs)

compiler/testData/ir/irText/expressions/callableReferenceWithArgumentsConversion.txt

@@ -0,0 +1,100 @@
+FILE fqName:<root> fileName:/callableReferenceWithArgumentsConversion.kt
+  FUN name:use visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Int, kotlin.String>) returnType:kotlin.String
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Int, kotlin.String>
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun use (fn: kotlin.Function1<kotlin.Int, kotlin.String>): kotlin.String declared in <root>'
+        CALL 'public abstract fun invoke (p1: P1 of kotlin.Function1): R of kotlin.Function1 [operator] declared in kotlin.Function1' type=kotlin.String origin=INVOKE
+          $this: GET_VAR 'fn: kotlin.Function1<kotlin.Int, kotlin.String> declared in <root>.use' type=kotlin.Function1<kotlin.Int, kotlin.String> origin=VARIABLE_AS_FUNCTION
+          p1: CONST Int type=kotlin.Int value=1
+  FUN name:coerceToUnit 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>
+    BLOCK_BODY
+  FUN name:fnWithDefault visibility:public modality:FINAL <> (a:kotlin.Int, b:kotlin.Int) returnType:kotlin.String
+    VALUE_PARAMETER name:a index:0 type:kotlin.Int
+    VALUE_PARAMETER name:b index:1 type:kotlin.Int
+      EXPRESSION_BODY
+        CONST Int type=kotlin.Int value=42
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun fnWithDefault (a: kotlin.Int, b: kotlin.Int): kotlin.String declared in <root>'
+        CONST String type=kotlin.String value="abc"
+  FUN name:fnWithVarargs visibility:public modality:FINAL <> (xs:kotlin.IntArray) returnType:kotlin.String
+    VALUE_PARAMETER name:xs index:0 type:kotlin.IntArray varargElementType:kotlin.Int [vararg]
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun fnWithVarargs (vararg xs: kotlin.Int): kotlin.String declared in <root>'
+        CONST String type=kotlin.String value="abc"
+  CLASS OBJECT name:Host modality:FINAL visibility:public superTypes:[kotlin.Any]
+    $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.Host
+    CONSTRUCTOR visibility:private <> () returnType:<root>.Host [primary]
+      BLOCK_BODY
+        DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
+        INSTANCE_INITIALIZER_CALL classDescriptor='CLASS OBJECT name:Host modality:FINAL visibility:public superTypes:[kotlin.Any]'
+    FUN name:importedObjectMemberWithVarargs visibility:public modality:FINAL <> ($this:<root>.Host, xs:kotlin.IntArray) returnType:kotlin.String
+      $this: VALUE_PARAMETER name:<this> type:<root>.Host
+      VALUE_PARAMETER name:xs index:0 type:kotlin.IntArray varargElementType:kotlin.Int [vararg]
+      BLOCK_BODY
+        RETURN type=kotlin.Nothing from='public final fun importedObjectMemberWithVarargs (vararg xs: kotlin.Int): kotlin.String declared in <root>.Host'
+          CONST String type=kotlin.String value="abc"
+    FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($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:testDefault visibility:public modality:FINAL <> () returnType:kotlin.String
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testDefault (): kotlin.String declared in <root>'
+        CALL 'public final fun use (fn: kotlin.Function1<kotlin.Int, kotlin.String>): kotlin.String declared in <root>' type=kotlin.String origin=null
+          fn: BLOCK type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.String> origin=null
+            FUN name:fnWithDefault visibility:local modality:FINAL <> (p0:kotlin.Int) returnType:kotlin.String
+              VALUE_PARAMETER name:p0 index:0 type:kotlin.Int
+              BLOCK_BODY
+                RETURN type=kotlin.Nothing from='local final fun fnWithDefault (p0: kotlin.Int): kotlin.String declared in <root>.testDefault'
+                  CALL 'public final fun fnWithDefault (a: kotlin.Int, b: kotlin.Int): kotlin.String declared in <root>' type=kotlin.String origin=null
+                    a: GET_VAR 'p0: kotlin.Int declared in <root>.testDefault.fnWithDefault' type=kotlin.Int origin=null
+            FUNCTION_REFERENCE 'local final fun fnWithDefault (p0: kotlin.Int): kotlin.String declared in <root>.testDefault' type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.String> origin=null
+  FUN name:testVararg visibility:public modality:FINAL <> () returnType:kotlin.String
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testVararg (): kotlin.String declared in <root>'
+        CALL 'public final fun use (fn: kotlin.Function1<kotlin.Int, kotlin.String>): kotlin.String declared in <root>' type=kotlin.String origin=null
+          fn: BLOCK type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.String> origin=null
+            FUN name:fnWithVarargs visibility:local modality:FINAL <> (p0:kotlin.Int) returnType:kotlin.String
+              VALUE_PARAMETER name:p0 index:0 type:kotlin.Int
+              BLOCK_BODY
+                RETURN type=kotlin.Nothing from='local final fun fnWithVarargs (p0: kotlin.Int): kotlin.String declared in <root>.testVararg'
+                  CALL 'public final fun fnWithVarargs (vararg xs: kotlin.Int): kotlin.String declared in <root>' type=kotlin.String origin=null
+                    xs: VARARG type=kotlin.IntArray varargElementType=kotlin.Int
+                      GET_VAR 'p0: kotlin.Int declared in <root>.testVararg.fnWithVarargs' type=kotlin.Int origin=null
+            FUNCTION_REFERENCE 'local final fun fnWithVarargs (p0: kotlin.Int): kotlin.String declared in <root>.testVararg' type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.String> origin=null
+  FUN name:testCoercionToUnit visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testCoercionToUnit (): kotlin.Unit declared in <root>'
+        CALL 'public final fun coerceToUnit (fn: kotlin.Function1<kotlin.Int, kotlin.Unit>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+          fn: BLOCK type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.Unit> origin=null
+            FUN name:fnWithDefault visibility:local modality:FINAL <> (p0:kotlin.Int) returnType:kotlin.Unit
+              VALUE_PARAMETER name:p0 index:0 type:kotlin.Int
+              BLOCK_BODY
+                TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
+                  CALL 'public final fun fnWithDefault (a: kotlin.Int, b: kotlin.Int): kotlin.String declared in <root>' type=kotlin.String origin=null
+                    a: GET_VAR 'p0: kotlin.Int declared in <root>.testCoercionToUnit.fnWithDefault' type=kotlin.Int origin=null
+            FUNCTION_REFERENCE 'local final fun fnWithDefault (p0: kotlin.Int): kotlin.Unit declared in <root>.testCoercionToUnit' type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.Unit> origin=null
+  FUN name:testImportedObjectMember visibility:public modality:FINAL <> () returnType:kotlin.String
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun testImportedObjectMember (): kotlin.String declared in <root>'
+        CALL 'public final fun use (fn: kotlin.Function1<kotlin.Int, kotlin.String>): kotlin.String declared in <root>' type=kotlin.String origin=null
+          fn: BLOCK type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.String> origin=null
+            FUN name:importedObjectMemberWithVarargs visibility:local modality:FINAL <> (p0:kotlin.Int) returnType:kotlin.String
+              VALUE_PARAMETER name:p0 index:0 type:kotlin.Int
+              BLOCK_BODY
+                RETURN type=kotlin.Nothing from='local final fun importedObjectMemberWithVarargs (p0: kotlin.Int): kotlin.String declared in <root>.testImportedObjectMember'
+                  CALL 'public final fun importedObjectMemberWithVarargs (vararg xs: kotlin.Int): kotlin.String declared in <root>.Host' type=kotlin.String origin=null
+                    $this: GET_OBJECT 'CLASS OBJECT name:Host modality:FINAL visibility:public superTypes:[kotlin.Any]' type=<root>.Host
+                    xs: VARARG type=kotlin.IntArray varargElementType=kotlin.Int
+                      GET_VAR 'p0: kotlin.Int declared in <root>.testImportedObjectMember.importedObjectMemberWithVarargs' type=kotlin.Int origin=null
+            FUNCTION_REFERENCE 'local final fun importedObjectMemberWithVarargs (p0: kotlin.Int): kotlin.String declared in <root>.testImportedObjectMember' type=kotlin.reflect.KFunction1<kotlin.Int, kotlin.String> origin=null

compiler/testData/ir/irText/expressions/callableReferenceWithVarargViewedAsArray.fir.txt

@@ -0,0 +1,74 @@
+FILE fqName:<root> fileName:/callableReferenceWithVarargViewedAsArray.kt
+  FUN name:sum visibility:public modality:FINAL <> (args:kotlin.IntArray) returnType:kotlin.Int
+    VALUE_PARAMETER name:args index:0 type:kotlin.IntArray
+    BLOCK_BODY
+      VAR name:result type:kotlin.Int [var]
+        CONST Int type=kotlin.Int value=0
+      VAR IR_TEMPORARY_VARIABLE name:tmp_0 type:kotlin.IntArray [val]
+        GET_VAR 'args: kotlin.IntArray declared in <root>.sum' type=kotlin.IntArray origin=null
+      VAR IR_TEMPORARY_VARIABLE name:tmp_1 type:kotlin.collections.IntIterator [val]
+        CALL 'public final fun iterator (): kotlin.collections.IntIterator [operator] declared in kotlin.IntArray' type=kotlin.collections.IntIterator origin=null
+          $this: GET_VAR 'val tmp_0: kotlin.IntArray [val] declared in <root>.sum' type=kotlin.IntArray origin=null
+      WHILE label=null origin=FOR_LOOP_INNER_WHILE
+        condition: CALL 'public abstract fun hasNext (): kotlin.Boolean [operator] declared in kotlin.collections.Iterator' type=kotlin.Boolean origin=null
+          $this: GET_VAR 'val tmp_1: kotlin.collections.IntIterator [val] declared in <root>.sum' type=kotlin.collections.IntIterator origin=null
+        body: BLOCK type=kotlin.Unit origin=null
+          VAR name:arg type:kotlin.Int [val]
+            CALL 'public final fun next (): kotlin.Int [operator] declared in kotlin.collections.IntIterator' type=kotlin.Int origin=null
+              $this: GET_VAR 'val tmp_1: kotlin.collections.IntIterator [val] declared in <root>.sum' type=kotlin.collections.IntIterator origin=null
+          SET_VAR 'var result: kotlin.Int [var] declared in <root>.sum' type=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: GET_VAR 'var result: kotlin.Int [var] declared in <root>.sum' type=kotlin.Int origin=null
+              other: GET_VAR 'val arg: kotlin.Int [val] declared in <root>.sum' type=kotlin.Int origin=null
+      RETURN type=kotlin.Nothing from='public final fun sum (args: kotlin.IntArray): kotlin.Int declared in <root>'
+        GET_VAR 'var result: kotlin.Int [var] declared in <root>.sum' type=kotlin.Int origin=null
+  FUN name:nsum visibility:public modality:FINAL <> (args:kotlin.Array<kotlin.Number>) returnType:kotlin.Int
+    VALUE_PARAMETER name:args index:0 type:kotlin.Array<kotlin.Number>
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun nsum (args: kotlin.Array<kotlin.Number>): kotlin.Int declared in <root>'
+        CALL 'public final fun sum (args: kotlin.IntArray): kotlin.Int declared in <root>' type=kotlin.Int origin=null
+          args: CONSTRUCTOR_CALL 'public constructor <init> (size: kotlin.Int, init: kotlin.Function1<kotlin.Int, kotlin.Int>) declared in kotlin.IntArray' type=kotlin.IntArray origin=null
+            size: CALL 'public final fun <get-size> (): kotlin.Int declared in kotlin.Array' type=kotlin.Int origin=null
+              $this: GET_VAR 'args: kotlin.Array<kotlin.Number> declared in <root>.nsum' type=kotlin.Array<kotlin.Number> origin=null
+            init: FUN_EXPR type=kotlin.Function1<kotlin.Int, kotlin.Int> origin=LAMBDA
+              FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> (it:kotlin.Int) returnType:kotlin.Int
+                VALUE_PARAMETER name:it index:0 type:kotlin.Int
+                BLOCK_BODY
+                  CALL 'public abstract fun toInt (): kotlin.Int declared in kotlin.Number' type=kotlin.Int origin=null
+                    $this: CALL 'public final fun get (index: kotlin.Int): kotlin.Number [operator] declared in kotlin.Array' type=kotlin.Number origin=null
+                      $this: GET_VAR 'args: kotlin.Array<kotlin.Number> declared in <root>.nsum' type=kotlin.Array<kotlin.Number> origin=null
+                      index: GET_VAR 'it: kotlin.Int declared in <root>.nsum.<anonymous>' type=kotlin.Int origin=null
+  FUN name:zap visibility:public modality:FINAL <> (b:kotlin.Array<kotlin.String>, k:kotlin.Int) returnType:kotlin.Unit
+    VALUE_PARAMETER name:b index:0 type:kotlin.Array<kotlin.String>
+    VALUE_PARAMETER name:k index:1 type:kotlin.Int
+      EXPRESSION_BODY
+        CONST Int type=kotlin.Int value=42
+    BLOCK_BODY
+  FUN name:usePlainArgs visibility:public modality:FINAL <> (fn:kotlin.Function2<kotlin.Int, kotlin.Int, kotlin.Int>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function2<kotlin.Int, kotlin.Int, kotlin.Int>
+    BLOCK_BODY
+  FUN name:usePrimitiveArray visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.IntArray, kotlin.Int>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.IntArray, kotlin.Int>
+    BLOCK_BODY
+  FUN name:useArray visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Array<kotlin.Int>, kotlin.Int>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Array<kotlin.Int>, kotlin.Int>
+    BLOCK_BODY
+  FUN name:useStringArray visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Array<kotlin.String>, kotlin.Unit>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Array<kotlin.String>, kotlin.Unit>
+    BLOCK_BODY
+  FUN name:testPlainArgs visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/usePlainArgs]>#' type=IrErrorType
+        FUNCTION_REFERENCE 'public final fun sum (args: kotlin.IntArray): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null
+  FUN name:testPrimitiveArrayAsVararg visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      CALL 'public final fun usePrimitiveArray (fn: kotlin.Function1<kotlin.IntArray, kotlin.Int>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+        fn: FUNCTION_REFERENCE 'public final fun sum (args: kotlin.IntArray): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null
+  FUN name:testArrayAsVararg visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/useArray]>#' type=IrErrorType
+        FUNCTION_REFERENCE 'public final fun nsum (args: kotlin.Array<kotlin.Number>): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.Array<kotlin.Number>, kotlin.Int> origin=null
+  FUN name:testArrayAndDefaults visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/useStringArray]>#' type=IrErrorType
+        FUNCTION_REFERENCE 'public final fun zap (b: kotlin.Array<kotlin.String>, k: kotlin.Int): kotlin.Unit declared in <root>' type=kotlin.reflect.KFunction2<kotlin.Array<kotlin.String>, kotlin.Int, kotlin.Unit> origin=null

compiler/testData/ir/irText/expressions/callableReferenceWithVarargViewedAsArray.kt

@@ -0,0 +1,22 @@
+// !LANGUAGE: +NewInference, +FunctionReferenceWithDefaultValueAsOtherType
+
+fun sum(vararg args: Int): Int {
+    var result = 0
+    for (arg in args)
+        result += arg
+    return result
+}
+
+fun nsum(vararg args: Number) = sum(*IntArray(args.size) { args[it].toInt() })
+
+fun zap(vararg b: String, k: Int = 42) {}
+
+fun usePlainArgs(fn: (Int, Int) -> Int) {}
+fun usePrimitiveArray(fn: (IntArray) -> Int) {}
+fun useArray(fn: (Array<Int>) -> Int) {}
+fun useStringArray(fn: (Array<String>) -> Unit) {}
+
+fun testPlainArgs() { usePlainArgs(::sum) }
+fun testPrimitiveArrayAsVararg() { usePrimitiveArray(::sum) }
+fun testArrayAsVararg() { useArray(::nsum) }
+fun testArrayAndDefaults() { useStringArray(::zap) }

compiler/testData/ir/irText/expressions/callableReferenceWithVarargViewedAsArray.txt

@@ -0,0 +1,94 @@
+FILE fqName:<root> fileName:/callableReferenceWithVarargViewedAsArray.kt
+  FUN name:sum visibility:public modality:FINAL <> (args:kotlin.IntArray) returnType:kotlin.Int
+    VALUE_PARAMETER name:args index:0 type:kotlin.IntArray varargElementType:kotlin.Int [vararg]
+    BLOCK_BODY
+      VAR name:result type:kotlin.Int [var]
+        CONST Int type=kotlin.Int value=0
+      BLOCK type=kotlin.Unit origin=FOR_LOOP
+        VAR FOR_LOOP_ITERATOR name:tmp_0 type:kotlin.collections.IntIterator [val]
+          CALL 'public final fun iterator (): kotlin.collections.IntIterator [operator] declared in kotlin.IntArray' type=kotlin.collections.IntIterator origin=FOR_LOOP_ITERATOR
+            $this: GET_VAR 'args: kotlin.IntArray [vararg] declared in <root>.sum' type=kotlin.IntArray origin=null
+        WHILE label=null origin=FOR_LOOP_INNER_WHILE
+          condition: CALL 'public abstract fun hasNext (): kotlin.Boolean [fake_override,operator] declared in kotlin.collections.IntIterator' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
+            $this: GET_VAR 'val tmp_0: kotlin.collections.IntIterator [val] declared in <root>.sum' type=kotlin.collections.IntIterator origin=null
+          body: BLOCK type=kotlin.Unit origin=FOR_LOOP_INNER_WHILE
+            VAR FOR_LOOP_VARIABLE name:arg type:kotlin.Int [val]
+              CALL 'public final fun next (): kotlin.Int [operator] declared in kotlin.collections.IntIterator' type=kotlin.Int origin=FOR_LOOP_NEXT
+                $this: GET_VAR 'val tmp_0: kotlin.collections.IntIterator [val] declared in <root>.sum' type=kotlin.collections.IntIterator origin=null
+            SET_VAR 'var result: kotlin.Int [var] declared in <root>.sum' type=kotlin.Unit origin=PLUSEQ
+              CALL 'public final fun plus (other: kotlin.Int): kotlin.Int [operator] declared in kotlin.Int' type=kotlin.Int origin=PLUSEQ
+                $this: GET_VAR 'var result: kotlin.Int [var] declared in <root>.sum' type=kotlin.Int origin=PLUSEQ
+                other: GET_VAR 'val arg: kotlin.Int [val] declared in <root>.sum' type=kotlin.Int origin=null
+      RETURN type=kotlin.Nothing from='public final fun sum (vararg args: kotlin.Int): kotlin.Int declared in <root>'
+        GET_VAR 'var result: kotlin.Int [var] declared in <root>.sum' type=kotlin.Int origin=null
+  FUN name:nsum visibility:public modality:FINAL <> (args:kotlin.Array<out kotlin.Number>) returnType:kotlin.Int
+    VALUE_PARAMETER name:args index:0 type:kotlin.Array<out kotlin.Number> varargElementType:kotlin.Number [vararg]
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun nsum (vararg args: kotlin.Number): kotlin.Int declared in <root>'
+        CALL 'public final fun sum (vararg args: kotlin.Int): kotlin.Int declared in <root>' type=kotlin.Int origin=null
+          args: VARARG type=kotlin.IntArray varargElementType=kotlin.Int
+            SPREAD_ELEMENT
+              CONSTRUCTOR_CALL 'public constructor <init> (size: kotlin.Int, init: kotlin.Function1<kotlin.Int, kotlin.Int>) declared in kotlin.IntArray' type=kotlin.IntArray origin=null
+                size: CALL 'public final fun <get-size> (): kotlin.Int declared in kotlin.Array' type=kotlin.Int origin=GET_PROPERTY
+                  $this: GET_VAR 'args: kotlin.Array<out kotlin.Number> [vararg] declared in <root>.nsum' type=kotlin.Array<out kotlin.Number> origin=null
+                init: FUN_EXPR type=kotlin.Function1<kotlin.Int, kotlin.Int> origin=LAMBDA
+                  FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> (it:kotlin.Int) returnType:kotlin.Int
+                    VALUE_PARAMETER name:it index:0 type:kotlin.Int
+                    BLOCK_BODY
+                      RETURN type=kotlin.Nothing from='local final fun <anonymous> (it: kotlin.Int): kotlin.Int declared in <root>.nsum'
+                        CALL 'public abstract fun toInt (): kotlin.Int declared in kotlin.Number' type=kotlin.Int origin=null
+                          $this: CALL 'public final fun get (index: kotlin.Int): T of kotlin.Array [operator] declared in kotlin.Array' type=kotlin.Number origin=GET_ARRAY_ELEMENT
+                            $this: GET_VAR 'args: kotlin.Array<out kotlin.Number> [vararg] declared in <root>.nsum' type=kotlin.Array<out kotlin.Number> origin=null
+                            index: GET_VAR 'it: kotlin.Int declared in <root>.nsum.<anonymous>' type=kotlin.Int origin=null
+  FUN name:zap visibility:public modality:FINAL <> (b:kotlin.Array<out kotlin.String>, k:kotlin.Int) returnType:kotlin.Unit
+    VALUE_PARAMETER name:b index:0 type:kotlin.Array<out kotlin.String> varargElementType:kotlin.String [vararg]
+    VALUE_PARAMETER name:k index:1 type:kotlin.Int
+      EXPRESSION_BODY
+        CONST Int type=kotlin.Int value=42
+    BLOCK_BODY
+  FUN name:usePlainArgs visibility:public modality:FINAL <> (fn:kotlin.Function2<kotlin.Int, kotlin.Int, kotlin.Int>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function2<kotlin.Int, kotlin.Int, kotlin.Int>
+    BLOCK_BODY
+  FUN name:usePrimitiveArray visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.IntArray, kotlin.Int>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.IntArray, kotlin.Int>
+    BLOCK_BODY
+  FUN name:useArray visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Array<kotlin.Int>, kotlin.Int>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Array<kotlin.Int>, kotlin.Int>
+    BLOCK_BODY
+  FUN name:useStringArray visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Array<kotlin.String>, kotlin.Unit>) returnType:kotlin.Unit
+    VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Array<kotlin.String>, kotlin.Unit>
+    BLOCK_BODY
+  FUN name:testPlainArgs visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      CALL 'public final fun usePlainArgs (fn: kotlin.Function2<kotlin.Int, kotlin.Int, kotlin.Int>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+        fn: BLOCK type=kotlin.reflect.KFunction2<kotlin.Int, kotlin.Int, kotlin.Int> origin=null
+          FUN name:sum visibility:local modality:FINAL <> (p0:kotlin.Int, p1:kotlin.Int) returnType:kotlin.Int
+            VALUE_PARAMETER name:p0 index:0 type:kotlin.Int
+            VALUE_PARAMETER name:p1 index:1 type:kotlin.Int
+            BLOCK_BODY
+              RETURN type=kotlin.Nothing from='local final fun sum (p0: kotlin.Int, p1: kotlin.Int): kotlin.Int declared in <root>.testPlainArgs'
+                CALL 'public final fun sum (vararg args: kotlin.Int): kotlin.Int declared in <root>' type=kotlin.Int origin=null
+                  args: VARARG type=kotlin.IntArray varargElementType=kotlin.Int
+                    GET_VAR 'p0: kotlin.Int declared in <root>.testPlainArgs.sum' type=kotlin.Int origin=null
+                    GET_VAR 'p1: kotlin.Int declared in <root>.testPlainArgs.sum' type=kotlin.Int origin=null
+          FUNCTION_REFERENCE 'local final fun sum (p0: kotlin.Int, p1: kotlin.Int): kotlin.Int declared in <root>.testPlainArgs' type=kotlin.reflect.KFunction2<kotlin.Int, kotlin.Int, kotlin.Int> origin=null
+  FUN name:testPrimitiveArrayAsVararg visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      CALL 'public final fun usePrimitiveArray (fn: kotlin.Function1<kotlin.IntArray, kotlin.Int>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+        fn: FUNCTION_REFERENCE 'public final fun sum (vararg args: kotlin.Int): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.IntArray, kotlin.Int> origin=null
+  FUN name:testArrayAsVararg visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      CALL 'public final fun useArray (fn: kotlin.Function1<kotlin.Array<kotlin.Int>, kotlin.Int>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+        fn: FUNCTION_REFERENCE 'public final fun nsum (vararg args: kotlin.Number): kotlin.Int declared in <root>' type=kotlin.reflect.KFunction1<kotlin.Array<out kotlin.Number>, kotlin.Int> origin=null
+  FUN name:testArrayAndDefaults visibility:public modality:FINAL <> () returnType:kotlin.Unit
+    BLOCK_BODY
+      CALL 'public final fun useStringArray (fn: kotlin.Function1<kotlin.Array<kotlin.String>, kotlin.Unit>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+        fn: BLOCK type=kotlin.reflect.KFunction1<kotlin.Array<out kotlin.String>, kotlin.Unit> origin=null
+          FUN name:zap visibility:local modality:FINAL <> (p0:kotlin.Array<out kotlin.String>) returnType:kotlin.Unit
+            VALUE_PARAMETER name:p0 index:0 type:kotlin.Array<out kotlin.String>
+            BLOCK_BODY
+              CALL 'public final fun zap (vararg b: kotlin.String, k: kotlin.Int): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
+                b: VARARG type=kotlin.Array<out kotlin.String> varargElementType=kotlin.String
+                  SPREAD_ELEMENT
+                    GET_VAR 'p0: kotlin.Array<out kotlin.String> declared in <root>.testArrayAndDefaults.zap' type=kotlin.Array<out kotlin.String> origin=null
+          FUNCTION_REFERENCE 'local final fun zap (p0: kotlin.Array<out kotlin.String>): kotlin.Unit declared in <root>.testArrayAndDefaults' type=kotlin.reflect.KFunction1<kotlin.Array<out kotlin.String>, kotlin.Unit> origin=null

compiler/tests/org/jetbrains/kotlin/ir/IrTextTestCaseGenerated.java

@@ -801,6 +801,16 @@ public class IrTextTestCaseGenerated extends AbstractIrTextTestCase {
             runTest("compiler/testData/ir/irText/expressions/callableReferenceTypeArguments.kt");
         }
 
+        @TestMetadata("callableReferenceWithArgumentsConversion.kt")
+        public void testCallableReferenceWithArgumentsConversion() throws Exception {
+            runTest("compiler/testData/ir/irText/expressions/callableReferenceWithArgumentsConversion.kt");
+        }
+
+        @TestMetadata("callableReferenceWithVarargViewedAsArray.kt")
+        public void testCallableReferenceWithVarargViewedAsArray() throws Exception {
+            runTest("compiler/testData/ir/irText/expressions/callableReferenceWithVarargViewedAsArray.kt");
+        }
+
         @TestMetadata("calls.kt")
         public void testCalls() throws Exception {
             runTest("compiler/testData/ir/irText/expressions/calls.kt");