FIR: Support SAM conversion

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt

@@ -0,0 +1,199 @@
+/*
+ * Copyright 2010-2019 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
+
+import org.jetbrains.kotlin.descriptors.ClassKind
+import org.jetbrains.kotlin.descriptors.Modality
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.FirSessionComponent
+import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
+import org.jetbrains.kotlin.fir.scopes.ProcessorAction
+import org.jetbrains.kotlin.fir.symbols.StandardClassIds
+import org.jetbrains.kotlin.fir.symbols.impl.ConeClassLikeLookupTagImpl
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
+import org.jetbrains.kotlin.fir.types.*
+import org.jetbrains.kotlin.fir.types.impl.ConeClassTypeImpl
+import org.jetbrains.kotlin.name.Name
+
+interface FirSamResolver : FirSessionComponent {
+    fun getFunctionTypeForPossibleSamType(type: ConeKotlinType): ConeKotlinType?
+    fun shouldRunSamConversionForFunction(firNamedFunction: FirNamedFunction): Boolean
+}
+
+private val NULL_STUB = Any()
+
+class FirSamResolverImpl(
+    private val firSession: FirSession,
+    private val scopeSession: ScopeSession
+) : FirSamResolver {
+
+    private val cache: MutableMap<FirRegularClass, Any> = mutableMapOf()
+
+    override fun getFunctionTypeForPossibleSamType(type: ConeKotlinType): ConeKotlinType? {
+        return when (type) {
+            is ConeClassType -> getFunctionTypeForPossibleSamType(type)
+            is ConeFlexibleType -> ConeFlexibleType(
+                getFunctionTypeForPossibleSamType(type.lowerBound) ?: return null,
+                getFunctionTypeForPossibleSamType(type.upperBound) ?: return null
+            )
+            is ConeClassErrorType -> null
+            // TODO: support those types as well
+            is ConeAbbreviatedType, is ConeTypeParameterType, is ConeTypeVariableType,
+            is ConeCapturedType, is ConeDefinitelyNotNullType, is ConeIntersectionType -> null
+            // TODO: Thing of getting rid of this branch since ConeLookupTagBasedType should be a sealed class
+            is ConeLookupTagBasedType -> null
+        }
+    }
+
+    private fun getFunctionTypeForPossibleSamType(type: ConeClassType): ConeLookupTagBasedType? {
+        val firRegularClass =
+            firSession.firSymbolProvider
+                .getSymbolByLookupTag(type.lookupTag)
+                ?.fir as? FirRegularClass
+                ?: return null
+
+        val unsubstitutedFunctionType = resolveFunctionTypeIfSamInterface(firRegularClass) ?: return null
+        val substitutor =
+            substitutorByMap(
+                firRegularClass.typeParameters
+                    .map { it.symbol }
+                    .zip(type.typeArguments.map {
+                        (it as? ConeTypedProjection)?.type
+                            ?: ConeClassTypeImpl(ConeClassLikeLookupTagImpl(StandardClassIds.Any), emptyArray(), isNullable = true)
+                    })
+                    .toMap()
+            )
+
+        val result =
+            substitutor
+                .substituteOrSelf(unsubstitutedFunctionType)
+                .withNullability(ConeNullability.create(type.isMarkedNullable))
+
+        require(result is ConeLookupTagBasedType) {
+            "Function type should always be ConeLookupTagBasedType, but ${result::class} was found"
+        }
+
+        return result
+    }
+
+    private fun resolveFunctionTypeIfSamInterface(firRegularClass: FirRegularClass): ConeKotlinType? {
+        return cache.getOrPut(firRegularClass) {
+            val abstractMethod = firRegularClass.getSingleAbstractMethodOrNull(firSession, scopeSession) ?: return@getOrPut NULL_STUB
+            // TODO: val shouldConvertFirstParameterToDescriptor = samWithReceiverResolvers.any { it.shouldConvertFirstSamParameterToReceiver(abstractMethod) }
+
+            abstractMethod.getFunctionTypeForAbstractMethod(firSession)
+        } as? ConeKotlinType
+    }
+
+    override fun shouldRunSamConversionForFunction(firNamedFunction: FirNamedFunction): Boolean {
+        // TODO: properly support, see org.jetbrains.kotlin.load.java.sam.JvmSamConversionTransformer.shouldRunSamConversionForFunction
+        return true
+    }
+}
+
+private fun FirRegularClass.getSingleAbstractMethodOrNull(
+    session: FirSession,
+    scopeSession: ScopeSession
+): FirNamedFunction? {
+    // TODO: restrict to Java interfaces
+    if (classKind != ClassKind.INTERFACE || hasMoreThenOneAbstractFunctionOrHasAbstractProperty()) return null
+
+    val samCandidateNames = computeSamCandidateNames(session)
+
+    return findSingleAbstractMethodByNames(session, scopeSession, samCandidateNames)
+}
+
+private fun FirRegularClass.computeSamCandidateNames(session: FirSession): Set<Name> {
+    val classes =
+        lookupSuperTypes(this, lookupInterfaces = true, deep = true, useSiteSession = session)
+            .mapNotNullTo(mutableListOf(this)) {
+                (session.firSymbolProvider.getSymbolByLookupTag(it.lookupTag) as? FirClassSymbol)?.fir
+            }
+
+    val samCandidateNames = mutableSetOf<Name>()
+    for (clazz in classes) {
+        for (declaration in clazz.declarations) {
+            if (declaration !is FirMemberDeclaration || declaration.modality != Modality.ABSTRACT) continue
+            samCandidateNames.add(declaration.name)
+        }
+    }
+
+    return samCandidateNames
+}
+
+private fun FirRegularClass.findSingleAbstractMethodByNames(
+    session: FirSession,
+    scopeSession: ScopeSession,
+    samCandidateNames: Set<Name>
+): FirNamedFunction? {
+    var resultMethod: FirNamedFunction? = null
+    var metIncorrectMember = false
+
+    val classUseSiteMemberScope = session.firSymbolProvider.getClassUseSiteMemberScope(classId, session, scopeSession)
+
+    for (candidateName in samCandidateNames) {
+        if (classUseSiteMemberScope == null) break
+        if (metIncorrectMember) break
+
+        classUseSiteMemberScope.processPropertiesByName(candidateName) {
+            if ((it as? FirProperty)?.modality == Modality.ABSTRACT) {
+                metIncorrectMember = true
+                ProcessorAction.STOP
+            } else {
+                ProcessorAction.NEXT
+            }
+        }
+
+        if (metIncorrectMember) break
+
+        classUseSiteMemberScope.processFunctionsByName(candidateName) { functionSymbol ->
+            val firFunction = functionSymbol.fir
+            require(firFunction is FirNamedFunction) {
+                "${functionSymbol.callableId.callableName} is expected to be FirNamedFunction, but ${functionSymbol::class} was found"
+            }
+
+            if (firFunction.modality != Modality.ABSTRACT) return@processFunctionsByName ProcessorAction.NEXT
+
+            if (resultMethod != null) {
+                metIncorrectMember = true
+                ProcessorAction.STOP
+            } else {
+                resultMethod = firFunction
+                ProcessorAction.NEXT
+            }
+        }
+    }
+
+    if (metIncorrectMember || resultMethod == null || resultMethod!!.typeParameters.isNotEmpty()) return null
+
+    return resultMethod
+}
+
+private fun FirRegularClass.hasMoreThenOneAbstractFunctionOrHasAbstractProperty(): Boolean {
+    var wasAbstractFunction = false
+    for (declaration in declarations) {
+        if (declaration is FirProperty && declaration.modality == Modality.ABSTRACT) return true
+        if (declaration is FirNamedFunction && declaration.modality == Modality.ABSTRACT) {
+            if (wasAbstractFunction) return true
+            wasAbstractFunction = true
+        }
+    }
+
+    return false
+}
+
+private fun FirNamedFunction.getFunctionTypeForAbstractMethod(session: FirSession): ConeLookupTagBasedType {
+    val parameterTypes = valueParameters.map {
+        it.returnTypeRef.coneTypeSafe<ConeKotlinType>() ?: ConeKotlinErrorType("No type for parameter $it")
+    }
+
+    return createFunctionalType(
+        session, parameterTypes,
+        receiverType = null,
+        rawReturnType = returnTypeRef.coneTypeSafe() ?: ConeKotlinErrorType("No type for return type of $this")
+    )
+}

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

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.fir.resolve.calls
 
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.FirAnonymousFunction
+import org.jetbrains.kotlin.fir.declarations.FirNamedFunction
 import org.jetbrains.kotlin.fir.declarations.FirValueParameter
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.resolve.transformers.firUnsafe
@@ -234,10 +235,32 @@ internal fun Candidate.resolveArgument(
 }
 
 private fun Candidate.prepareExpectedType(session: FirSession, argument: FirExpression, parameter: FirValueParameter): ConeKotlinType {
-    val expectedType = argument.getExpectedType(session, parameter/*, LanguageVersionSettings*/)
+    val basicExpectedType = argument.getExpectedType(session, parameter/*, LanguageVersionSettings*/)
+    val expectedType = getExpectedTypeWithSAMConversion(session, argument, basicExpectedType) ?: basicExpectedType
     return this.substitutor.substituteOrSelf(expectedType)
 }
 
+private fun Candidate.getExpectedTypeWithSAMConversion(
+    session: FirSession,
+    argument: FirExpression,
+    candidateExpectedType: ConeKotlinType
+): ConeKotlinType? {
+    if (candidateExpectedType.isBuiltinFunctionalType) return null
+    // TODO: if (!callComponents.languageVersionSettings.supportsFeature(LanguageFeature.SamConversionPerArgument)) return null
+    val firNamedFunction = symbol.fir as? FirNamedFunction ?: return null
+    if (!samResolver.shouldRunSamConversionForFunction(firNamedFunction)) return null
+
+    val argumentIsFunctional = when ((argument as? FirWrappedArgumentExpression)?.expression ?: argument) {
+        is FirAnonymousFunction, is FirCallableReferenceAccess -> true
+        else -> argument.typeRef.coneTypeSafe<ConeKotlinType>()?.isBuiltinFunctionalType == true
+    }
+    if (!argumentIsFunctional) return null
+
+    // TODO: resolvedCall.registerArgumentWithSamConversion(argument, SamConversionDescription(convertedTypeByOriginal, convertedTypeByCandidate!!))
+
+    return samResolver.getFunctionTypeForPossibleSamType(candidateExpectedType) ?: return null
+}
+
 internal fun FirExpression.getExpectedType(
     session: FirSession,
     parameter: FirValueParameter/*, languageVersionSettings: LanguageVersionSettings*/

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

@@ -58,6 +58,9 @@ class Candidate(
         system.addOtherSystem(baseSystem)
         system
     }
+
+    val samResolver get() = inferenceComponents.samResolver
+
     lateinit var substitutor: ConeSubstitutor
 
     var argumentMapping: Map<FirExpression, FirValueParameter>? = null

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

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.fir.resolve.calls
 
 import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.resolve.FirSamResolver
 import org.jetbrains.kotlin.fir.resolve.ScopeSession
 import org.jetbrains.kotlin.fir.resolve.toSymbol
 import org.jetbrains.kotlin.fir.resolve.transformers.ReturnTypeCalculator
@@ -57,7 +58,8 @@ class InferenceComponents(
     val ctx: TypeSystemInferenceExtensionContextDelegate,
     val session: FirSession,
     val returnTypeCalculator: ReturnTypeCalculator,
-    val scopeSession: ScopeSession
+    val scopeSession: ScopeSession,
+    val samResolver: FirSamResolver
 ) {
     private val approximator = object : AbstractTypeApproximator(ctx) {
         override fun createErrorType(message: String): SimpleTypeMarker {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirBodyResolveTransformer.kt

@@ -978,7 +978,7 @@ private fun inferenceComponents(session: FirSession, returnTypeCalculator: Retur
             require(this is ErrorTypeConstructor)
             return ConeClassErrorType(reason)
         }
-    }, session, returnTypeCalculator, scopeSession)
+    }, session, returnTypeCalculator, scopeSession, FirSamResolverImpl(session, scopeSession))
 
 
 class FirDesignatedBodyResolveTransformer(

compiler/fir/resolve/testData/diagnostics/samConversions/genericSam.kt

@@ -0,0 +1,41 @@
+// FILE: MyFunction.java
+public interface MyFunction<T, R> {
+    R foo(T x);
+}
+
+// FILE: JavaUsage.java
+
+public class JavaUsage {
+    public static void foo1(MyFunction<Integer, String> x) {}
+    public static void foo2(MyFunction<? super Number, ? extends CharSequence> x) {}
+    public static <X, Y> Y foo3(MyFunction<X, Y> f, X x) {}
+}
+// FILE: main.kt
+
+fun main() {
+    JavaUsage.foo1 { x ->
+        x.toInt().toString()
+    }
+
+    JavaUsage.foo2 { x ->
+        x.toInt().toString()
+    }
+
+    JavaUsage.foo2 { x: Int ->
+        x.toString()
+    }
+
+    JavaUsage.foo3(
+        { x ->
+            (x + 1).toString()
+        },
+        1
+    )
+
+    JavaUsage.foo3(
+        { x: Number ->
+            x.toInt().toString()
+        },
+        2
+    )
+}

compiler/fir/resolve/testData/diagnostics/samConversions/genericSam.txt

@@ -0,0 +1,23 @@
+FILE: main.kt
+    public final fun main(): R|kotlin/Unit| {
+        Q|JavaUsage|.R|/JavaUsage.foo1|(<L> = foo1@fun <anonymous>(x: R|ft<kotlin/Int, kotlin/Int?>!|): R|ft<kotlin/String, kotlin/String?>!| <kind=EXACTLY_ONCE>  {
+            R|<local>/x|.R|kotlin/Int.toInt|().R|kotlin/Any.toString|()
+        }
+        )
+        Q|JavaUsage|.R|/JavaUsage.foo2|(<L> = foo2@fun <anonymous>(x: R|ft<kotlin/Number, kotlin/Number?>!|): R|ft<kotlin/CharSequence, kotlin/CharSequence?>!| <kind=EXACTLY_ONCE>  {
+            R|<local>/x|.R|kotlin/Number.toInt|().R|kotlin/Any.toString|()
+        }
+        )
+        Q|JavaUsage|.R|/JavaUsage.foo2|(<L> = foo2@fun <anonymous>(x: R|kotlin/Int|): R|ft<kotlin/CharSequence, kotlin/CharSequence?>!| <kind=EXACTLY_ONCE>  {
+            R|<local>/x|.R|kotlin/Any.toString|()
+        }
+        )
+        Q|JavaUsage|.R|/JavaUsage.foo3|<R|ft<kotlin/Int, kotlin/Int>|, R|ft<kotlin/String, kotlin/String>|>(foo3@fun <anonymous>(x: R|ft<kotlin/Int, kotlin/Int>|): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+            R|<local>/x|.R|kotlin/Int.plus|(Int(1)).R|kotlin/Any.toString|()
+        }
+        , Int(1))
+        Q|JavaUsage|.R|/JavaUsage.foo3|<R|ft<kotlin/Int, kotlin/Int>|, R|ft<kotlin/String, kotlin/String>|>(foo3@fun <anonymous>(x: R|kotlin/Number|): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+            R|<local>/x|.R|kotlin/Number.toInt|().R|kotlin/Any.toString|()
+        }
+        , Int(2))
+    }

compiler/fir/resolve/testData/diagnostics/samConversions/kotlinSam.kt

@@ -0,0 +1,42 @@
+// TODO: These interfaces must be marked as "fun" ones that modifier is supported
+interface MyRunnable {
+    fun foo(x: Int): Boolean
+}
+
+interface WithProperty {
+    val x: Int
+}
+
+interface TwoAbstract : MyRunnable {
+    fun bar()
+}
+
+interface Super {
+    fun foo(x: Int): Any
+}
+
+interface Derived : Super {
+    override fun foo(x: Int): Boolean
+}
+
+fun foo1(m: MyRunnable) {}
+fun foo2(m: WithProperty) {}
+fun foo3(m: TwoAbstract) {}
+fun foo3(m: Derived) {}
+
+fun main() {
+    val f = { t: Int -> t > 1}
+
+    foo1 { x -> x > 1 }
+    foo1(f)
+
+    foo2 { x -> x > 1 }
+    foo2(f)
+
+    foo3 { x -> x > 1 }
+    foo3(f)
+
+    foo4 { x -> x > 1 }
+    foo4(f)
+
+}

compiler/fir/resolve/testData/diagnostics/samConversions/kotlinSam.txt

@@ -0,0 +1,56 @@
+FILE: kotlinSam.kt
+    public abstract interface MyRunnable : R|kotlin/Any| {
+        public abstract fun foo(x: R|kotlin/Int|): R|kotlin/Boolean|
+
+    }
+    public abstract interface WithProperty : R|kotlin/Any| {
+        public abstract val x: R|kotlin/Int|
+            public get(): R|kotlin/Int|
+
+    }
+    public abstract interface TwoAbstract : R|MyRunnable| {
+        public abstract fun bar(): R|kotlin/Unit|
+
+    }
+    public abstract interface Super : R|kotlin/Any| {
+        public abstract fun foo(x: R|kotlin/Int|): R|kotlin/Any|
+
+    }
+    public abstract interface Derived : R|Super| {
+        public abstract override fun foo(x: R|kotlin/Int|): R|kotlin/Boolean|
+
+    }
+    public final fun foo1(m: R|MyRunnable|): R|kotlin/Unit| {
+    }
+    public final fun foo2(m: R|WithProperty|): R|kotlin/Unit| {
+    }
+    public final fun foo3(m: R|TwoAbstract|): R|kotlin/Unit| {
+    }
+    public final fun foo3(m: R|Derived|): R|kotlin/Unit| {
+    }
+    public final fun main(): R|kotlin/Unit| {
+        lval f: R|kotlin/Function1<kotlin/Int, kotlin/Boolean>| = fun <anonymous>(t: R|kotlin/Int|): kotlin/Boolean {
+            >(R|<local>/t|, Int(1))
+        }
+
+        R|/foo1|(<L> = foo1@fun <anonymous>(x: R|kotlin/Int|): R|kotlin/Boolean| <kind=EXACTLY_ONCE>  {
+            >(R|<local>/x|, Int(1))
+        }
+        )
+        R|/foo1|(R|<local>/f|)
+        R|/foo2|(<L> = foo2@fun <anonymous>(x: R|kotlin/Nothing|): kotlin/Boolean <kind=EXACTLY_ONCE>  {
+            >(R|<local>/x|, Int(1))
+        }
+        )
+        <Inapplicable(INAPPLICABLE): [/foo2]>#(R|<local>/f|)
+        <Ambiguity: foo3, [/foo3, /foo3]>#(<L> = foo3@fun <implicit>.<anonymous>(x: <implicit>): <implicit> <kind=EXACTLY_ONCE>  {
+            >(x#, Int(1))
+        }
+        )
+        R|/foo3|(R|<local>/f|)
+        <Unresolved name: foo4>#(<L> = foo4@fun <implicit>.<anonymous>(x: <implicit>): <implicit> <kind=EXACTLY_ONCE>  {
+            >(x#, Int(1))
+        }
+        )
+        <Unresolved name: foo4>#(R|<local>/f|)
+    }

compiler/fir/resolve/testData/diagnostics/samConversions/notSamBecauseOfSupertype.kt

@@ -0,0 +1,31 @@
+// FILE: MyRunnable.java
+public interface MyRunnable {
+    void bar();
+}
+
+// FILE: DerivedRunnable.java
+public interface DerivedRunnable extends MyRunnable {
+    boolean foo(int x);
+}
+
+// FILE: JavaUsage.java
+
+public class JavaUsage {
+    public static void foo(DerivedRunnable x) {}
+}
+// FILE: main.kt
+
+fun foo(m: MyRunnable) {}
+
+fun main() {
+    JavaUsage.foo {
+            x ->
+        x > 1
+    }
+
+    JavaUsage.foo({ it > 1 })
+
+    val x = { x: Int -> x > 1 }
+
+    JavaUsage.foo(x)
+}

compiler/fir/resolve/testData/diagnostics/samConversions/notSamBecauseOfSupertype.txt

@@ -0,0 +1,18 @@
+FILE: main.kt
+    public final fun foo(m: R|MyRunnable|): R|kotlin/Unit| {
+    }
+    public final fun main(): R|kotlin/Unit| {
+        Q|JavaUsage|.R|/JavaUsage.foo|(<L> = foo@fun <anonymous>(x: R|kotlin/Nothing|): kotlin/Boolean <kind=EXACTLY_ONCE>  {
+            >(R|<local>/x|, Int(1))
+        }
+        )
+        Q|JavaUsage|.R|/JavaUsage.foo|(foo@fun <anonymous>(): kotlin/Boolean <kind=EXACTLY_ONCE>  {
+            >(<Unresolved name: it>#, Int(1))
+        }
+        )
+        lval x: R|kotlin/Function1<kotlin/Int, kotlin/Boolean>| = fun <anonymous>(x: R|kotlin/Int|): kotlin/Boolean {
+            >(R|<local>/x|, Int(1))
+        }
+
+        Q|JavaUsage|.<Inapplicable(INAPPLICABLE): [/JavaUsage.foo]>#(R|<local>/x|)
+    }

compiler/fir/resolve/testData/diagnostics/samConversions/runnable.kt

@@ -0,0 +1,16 @@
+// FILE: JavaClass.java
+public class JavaClass {
+    public static void foo(Runnable x) {}
+    public void bar(Runnable x) {}
+}
+
+// FILE: main.kt
+fun main() {
+    JavaClass.foo {
+        ""
+    }
+
+    JavaClass().bar {
+        ""
+    }
+}

compiler/fir/resolve/testData/diagnostics/samConversions/runnable.txt

@@ -0,0 +1,11 @@
+FILE: main.kt
+    public final fun main(): R|kotlin/Unit| {
+        Q|JavaClass|.R|/JavaClass.foo|(<L> = foo@fun <anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+            String()
+        }
+        )
+        R|/JavaClass.JavaClass|().R|/JavaClass.bar|(<L> = bar@fun <anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+            String()
+        }
+        )
+    }

compiler/fir/resolve/testData/diagnostics/samConversions/samSupertype.kt

@@ -0,0 +1,32 @@
+// FILE: MyRunnable.java
+public interface MyRunnable {
+    boolean foo(int x);
+    default void bar() {}
+}
+
+// FILE: DerivedRunnable.java
+public interface DerivedRunnable extends MyRunnable {
+    default void baz() {}
+}
+
+// FILE: JavaUsage.java
+
+public class JavaUsage {
+    public static void foo(DerivedRunnable x) {}
+}
+// FILE: main.kt
+
+fun foo(m: MyRunnable) {}
+
+fun main() {
+    JavaUsage.foo {
+            x ->
+        x > 1
+    }
+
+    JavaUsage.foo({ it > 1 })
+
+    val x = { x: Int -> x > 1 }
+
+    JavaUsage.foo(x)
+}

compiler/fir/resolve/testData/diagnostics/samConversions/samSupertype.txt

@@ -0,0 +1,18 @@
+FILE: main.kt
+    public final fun foo(m: R|MyRunnable|): R|kotlin/Unit| {
+    }
+    public final fun main(): R|kotlin/Unit| {
+        Q|JavaUsage|.R|/JavaUsage.foo|(<L> = foo@fun <anonymous>(x: R|kotlin/Int|): R|kotlin/Boolean| <kind=EXACTLY_ONCE>  {
+            >(R|<local>/x|, Int(1))
+        }
+        )
+        Q|JavaUsage|.R|/JavaUsage.foo|(foo@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/Boolean| <kind=EXACTLY_ONCE>  {
+            >(R|<local>/it|, Int(1))
+        }
+        )
+        lval x: R|kotlin/Function1<kotlin/Int, kotlin/Boolean>| = fun <anonymous>(x: R|kotlin/Int|): kotlin/Boolean {
+            >(R|<local>/x|, Int(1))
+        }
+
+        Q|JavaUsage|.R|/JavaUsage.foo|(R|<local>/x|)
+    }

compiler/fir/resolve/testData/diagnostics/samConversions/samSupertypeWithOverride.kt

@@ -0,0 +1,34 @@
+// FILE: MyRunnable.java
+public interface MyRunnable {
+    Object foo(int x);
+    default void bar() {}
+}
+
+// FILE: DerivedRunnable.java
+public interface DerivedRunnable extends MyRunnable {
+    @Override
+    Boolean foo(int x);
+    default void baz() {}
+}
+
+// FILE: JavaUsage.java
+
+public class JavaUsage {
+    public static void foo(DerivedRunnable x) {}
+}
+// FILE: main.kt
+
+fun foo(m: MyRunnable) {}
+
+fun main() {
+    JavaUsage.foo {
+            x ->
+        x > 1
+    }
+
+    JavaUsage.foo({ it > 1 })
+
+    val x = { x: Int -> x > 1 }
+
+    JavaUsage.foo(x)
+}

compiler/fir/resolve/testData/diagnostics/samConversions/samSupertypeWithOverride.txt

@@ -0,0 +1,18 @@
+FILE: main.kt
+    public final fun foo(m: R|MyRunnable|): R|kotlin/Unit| {
+    }
+    public final fun main(): R|kotlin/Unit| {
+        Q|JavaUsage|.R|/JavaUsage.foo|(<L> = foo@fun <anonymous>(x: R|kotlin/Int|): R|ft<kotlin/Boolean, kotlin/Boolean?>!| <kind=EXACTLY_ONCE>  {
+            >(R|<local>/x|, Int(1))
+        }
+        )
+        Q|JavaUsage|.R|/JavaUsage.foo|(foo@fun <anonymous>(it: R|kotlin/Int|): R|ft<kotlin/Boolean, kotlin/Boolean?>!| <kind=EXACTLY_ONCE>  {
+            >(R|<local>/it|, Int(1))
+        }
+        )
+        lval x: R|kotlin/Function1<kotlin/Int, kotlin/Boolean>| = fun <anonymous>(x: R|kotlin/Int|): kotlin/Boolean {
+            >(R|<local>/x|, Int(1))
+        }
+
+        Q|JavaUsage|.R|/JavaUsage.foo|(R|<local>/x|)
+    }

compiler/fir/resolve/testData/diagnostics/samConversions/simple.kt

@@ -0,0 +1,26 @@
+// FILE: MyRunnable.java
+public interface MyRunnable {
+    boolean foo(int x);
+}
+
+// FILE: JavaUsage.java
+
+public class JavaUsage {
+    public static void foo(MyRunnable x) {}
+}
+// FILE: main.kt
+
+fun foo(m: MyRunnable) {}
+
+fun main() {
+    JavaUsage.foo {
+        x ->
+        x > 1
+    }
+
+    JavaUsage.foo({ it > 1 })
+
+    val x = { x: Int -> x > 1 }
+
+    JavaUsage.foo(x)
+}

compiler/fir/resolve/testData/diagnostics/samConversions/simple.txt

@@ -0,0 +1,18 @@
+FILE: main.kt
+    public final fun foo(m: R|MyRunnable|): R|kotlin/Unit| {
+    }
+    public final fun main(): R|kotlin/Unit| {
+        Q|JavaUsage|.R|/JavaUsage.foo|(<L> = foo@fun <anonymous>(x: R|kotlin/Int|): R|kotlin/Boolean| <kind=EXACTLY_ONCE>  {
+            >(R|<local>/x|, Int(1))
+        }
+        )
+        Q|JavaUsage|.R|/JavaUsage.foo|(foo@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/Boolean| <kind=EXACTLY_ONCE>  {
+            >(R|<local>/it|, Int(1))
+        }
+        )
+        lval x: R|kotlin/Function1<kotlin/Int, kotlin/Boolean>| = fun <anonymous>(x: R|kotlin/Int|): kotlin/Boolean {
+            >(R|<local>/x|, Int(1))
+        }
+
+        Q|JavaUsage|.R|/JavaUsage.foo|(R|<local>/x|)
+    }

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java

@@ -91,4 +91,52 @@ public class FirDiagnosticsTestGenerated extends AbstractFirDiagnosticsTest {
             runTest("compiler/fir/resolve/testData/diagnostics/j+k/outerInnerClasses.kt");
         }
     }
+
+    @TestMetadata("compiler/fir/resolve/testData/diagnostics/samConversions")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class SamConversions extends AbstractFirDiagnosticsTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, TargetBackend.ANY, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInSamConversions() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/fir/resolve/testData/diagnostics/samConversions"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
+        }
+
+        @TestMetadata("genericSam.kt")
+        public void testGenericSam() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/samConversions/genericSam.kt");
+        }
+
+        @TestMetadata("kotlinSam.kt")
+        public void testKotlinSam() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/samConversions/kotlinSam.kt");
+        }
+
+        @TestMetadata("notSamBecauseOfSupertype.kt")
+        public void testNotSamBecauseOfSupertype() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/samConversions/notSamBecauseOfSupertype.kt");
+        }
+
+        @TestMetadata("runnable.kt")
+        public void testRunnable() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/samConversions/runnable.kt");
+        }
+
+        @TestMetadata("samSupertype.kt")
+        public void testSamSupertype() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/samConversions/samSupertype.kt");
+        }
+
+        @TestMetadata("samSupertypeWithOverride.kt")
+        public void testSamSupertypeWithOverride() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/samConversions/samSupertypeWithOverride.kt");
+        }
+
+        @TestMetadata("simple.kt")
+        public void testSimple() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/samConversions/simple.kt");
+        }
+    }
 }

compiler/testData/ir/irText/expressions/sam/samByProjectedType.fir.txt

@@ -2,8 +2,8 @@ FILE fqName:<root> fileName:/samByProjectedType.kt
   FUN name:test1 visibility:public modality:FINAL <> () returnType:kotlin.Unit
     BLOCK_BODY
       CALL 'public open fun bar (j: <root>.J<*>?): kotlin.Unit declared in <root>.H' type=kotlin.Unit origin=null
-        j: FUN_EXPR type=kotlin.Function1<kotlin.Any, kotlin.Any> origin=LAMBDA
+        j: FUN_EXPR type=kotlin.Function1<kotlin.Any, kotlin.Any?> origin=LAMBDA
-          FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> (x:kotlin.Any) returnType:kotlin.Any
+          FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> (x:kotlin.Any) returnType:kotlin.Any?
             VALUE_PARAMETER name:x index:0 type:kotlin.Any
             BLOCK_BODY
               GET_VAR 'x: kotlin.Any declared in <root>.test1.<anonymous>' type=kotlin.Any origin=null

compiler/testData/ir/irText/expressions/sam/samConversionToGeneric.fir.txt

@@ -38,22 +38,22 @@ FILE fqName:<root> fileName:/samConversionToGeneric.kt
     BLOCK_BODY
       TYPE_OP type=kotlin.Function1<kotlin.String, kotlin.String> origin=CAST typeOperand=kotlin.Function1<kotlin.String, kotlin.String>
         GET_VAR 'a: kotlin.Any declared in <root>.test5' type=kotlin.Any origin=null
-      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/H.bar]>#' type=IrErrorType
+      CALL 'public open fun bar (j: <root>.J<X of <uninitialized parent>?>?): kotlin.Unit declared in <root>.H' type=kotlin.Unit origin=null
-        GET_VAR 'a: kotlin.Any declared in <root>.test5' type=kotlin.Function1<kotlin.String, kotlin.String> origin=null
+        j: GET_VAR 'a: kotlin.Any declared in <root>.test5' type=kotlin.Function1<kotlin.String, kotlin.String> origin=null
   FUN name:test6 visibility:public modality:FINAL <T> (a:kotlin.Function1<T of <root>.test6, T of <root>.test6>) returnType:kotlin.Unit
     TYPE_PARAMETER name:T index:0 variance: superTypes:[]
     VALUE_PARAMETER name:a index:0 type:kotlin.Function1<T of <root>.test6, T of <root>.test6>
     BLOCK_BODY
-      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/H.bar]>#' type=IrErrorType
+      CALL 'public open fun bar (j: <root>.J<X of <uninitialized parent>?>?): kotlin.Unit declared in <root>.H' type=kotlin.Unit origin=null
-        GET_VAR 'a: kotlin.Function1<T of <root>.test6, T of <root>.test6> declared in <root>.test6' type=kotlin.Function1<T of <root>.test6, T of <root>.test6> origin=null
+        j: GET_VAR 'a: kotlin.Function1<T of <root>.test6, T of <root>.test6> declared in <root>.test6' type=kotlin.Function1<T of <root>.test6, T of <root>.test6> origin=null
   FUN name:test7 visibility:public modality:FINAL <T> (a:kotlin.Any) returnType:kotlin.Unit
     TYPE_PARAMETER name:T index:0 variance: superTypes:[]
     VALUE_PARAMETER name:a index:0 type:kotlin.Any
     BLOCK_BODY
       TYPE_OP type=kotlin.Function1<T of <root>.test7, T of <root>.test7> origin=CAST typeOperand=kotlin.Function1<T of <root>.test7, T of <root>.test7>
         GET_VAR 'a: kotlin.Any declared in <root>.test7' type=kotlin.Any origin=null
-      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/H.bar]>#' type=IrErrorType
+      CALL 'public open fun bar (j: <root>.J<X of <uninitialized parent>?>?): kotlin.Unit declared in <root>.H' type=kotlin.Unit origin=null
-        GET_VAR 'a: kotlin.Any declared in <root>.test7' type=kotlin.Function1<T of <root>.test7, T of <root>.test7> origin=null
+        j: GET_VAR 'a: kotlin.Any declared in <root>.test7' type=kotlin.Function1<T of <root>.test7, T of <root>.test7> origin=null
   FUN name:test8 visibility:public modality:FINAL <> (efn:kotlin.Function1<kotlin.String, kotlin.String>) returnType:IrErrorType
     VALUE_PARAMETER name:efn index:0 type:kotlin.Function1<kotlin.String, kotlin.String>
     BLOCK_BODY
@@ -63,8 +63,8 @@ FILE fqName:<root> fileName:/samConversionToGeneric.kt
   FUN name:test9 visibility:public modality:FINAL <> (efn:kotlin.Function1<kotlin.String, kotlin.String>) returnType:kotlin.Unit
     VALUE_PARAMETER name:efn index:0 type:kotlin.Function1<kotlin.String, kotlin.String>
     BLOCK_BODY
-      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/H.bar]>#' type=IrErrorType
+      CALL 'public open fun bar (j: <root>.J<X of <uninitialized parent>?>?): kotlin.Unit declared in <root>.H' type=kotlin.Unit origin=null
-        GET_VAR 'efn: kotlin.Function1<kotlin.String, kotlin.String> declared in <root>.test9' type=kotlin.Function1<kotlin.String, kotlin.String> origin=null
+        j: GET_VAR 'efn: kotlin.Function1<kotlin.String, kotlin.String> declared in <root>.test9' type=kotlin.Function1<kotlin.String, kotlin.String> origin=null
   FUN name:test10 visibility:public modality:FINAL <> (fn:kotlin.Function1<kotlin.Int, kotlin.String>) returnType:kotlin.Unit
     VALUE_PARAMETER name:fn index:0 type:kotlin.Function1<kotlin.Int, kotlin.String>
     BLOCK_BODY

compiler/testData/ir/irText/expressions/sam/samConversions.fir.txt

@@ -28,17 +28,19 @@ FILE fqName:<root> fileName:/samConversions.kt
     $receiver: VALUE_PARAMETER name:<this> type:<root>.J
     VALUE_PARAMETER name:a index:0 type:kotlin.Function0<kotlin.Unit>
     BLOCK_BODY
-      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/J.run2]>#' type=IrErrorType
+      CALL 'public open fun run2 (r1: java.lang.Runnable?, r2: java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
-        GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test3' type=kotlin.Function0<kotlin.Unit> origin=null
+        $this: GET_VAR '<this>: <root>.J declared in <root>.J' type=<root>.J origin=null
-        GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test3' type=kotlin.Function0<kotlin.Unit> origin=null
+        r1: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test3' type=kotlin.Function0<kotlin.Unit> origin=null
+        r2: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test3' type=kotlin.Function0<kotlin.Unit> origin=null
   FUN name:test4 visibility:public modality:FINAL <> ($receiver:<root>.J, a:kotlin.Function0<kotlin.Unit>, b:kotlin.Function0<kotlin.Unit>, flag:kotlin.Boolean) returnType:kotlin.Unit
     $receiver: VALUE_PARAMETER name:<this> type:<root>.J
     VALUE_PARAMETER name:a index:0 type:kotlin.Function0<kotlin.Unit>
     VALUE_PARAMETER name:b index:1 type:kotlin.Function0<kotlin.Unit>
     VALUE_PARAMETER name:flag index:2 type:kotlin.Boolean
     BLOCK_BODY
-      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/J.runIt]>#' type=IrErrorType
+      CALL 'public open fun runIt (r: java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
-        WHEN type=kotlin.Function0<kotlin.Unit> origin=IF
+        $this: GET_VAR '<this>: <root>.J declared in <root>.J' type=<root>.J origin=null
+        r: WHEN type=kotlin.Function0<kotlin.Unit> origin=IF
           BRANCH
             if: GET_VAR 'flag: kotlin.Boolean declared in <root>.test4' type=kotlin.Boolean origin=null
             then: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test4' type=kotlin.Function0<kotlin.Unit> origin=null

compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.fir.txt

@@ -33,13 +33,14 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
     VALUE_PARAMETER name:a index:0 type:kotlin.Function0<kotlin.Unit>
     VALUE_PARAMETER name:b index:1 type:kotlin.Function0<kotlin.Unit>
     BLOCK_BODY
-      WHEN type=IrErrorType origin=IF
+      WHEN type=kotlin.Unit origin=IF
         BRANCH
           if: TYPE_OP type=kotlin.Boolean origin=INSTANCEOF typeOperand=java.lang.Runnable
             GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test4' type=kotlin.Function0<kotlin.Unit> origin=null
-          then: ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/J.run2]>#' type=IrErrorType
+          then: CALL 'public open fun run2 (r1: java.lang.Runnable?, r2: java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
-            GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test4' type=java.lang.Runnable origin=null
+            $this: CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in <root>.J' type=<root>.J origin=null
-            GET_VAR 'b: kotlin.Function0<kotlin.Unit> declared in <root>.test4' type=kotlin.Function0<kotlin.Unit> origin=null
+            r1: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test4' type=java.lang.Runnable origin=null
+            r2: GET_VAR 'b: kotlin.Function0<kotlin.Unit> declared in <root>.test4' type=kotlin.Function0<kotlin.Unit> origin=null
   FUN name:test5 visibility:public modality:FINAL <> (a:kotlin.Any) returnType:kotlin.Unit
     VALUE_PARAMETER name:a index:0 type:kotlin.Any
     BLOCK_BODY
@@ -68,8 +69,9 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
     BLOCK_BODY
       TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=CAST typeOperand=kotlin.Function0<kotlin.Unit>
         GET_VAR 'a: kotlin.Any declared in <root>.test6' type=kotlin.Any origin=null
-      ERROR_CALL 'Unresolved reference: <Inapplicable(INAPPLICABLE): [/J.run1]>#' type=IrErrorType
+      CALL 'public open fun run1 (r: java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
-        GET_VAR 'a: kotlin.Any declared in <root>.test6' type=kotlin.Function0<kotlin.Unit> origin=null
+        $this: CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in <root>.J' type=<root>.J origin=null
+        r: GET_VAR 'a: kotlin.Any declared in <root>.test6' type=kotlin.Function0<kotlin.Unit> origin=null
   FUN name:test7 visibility:public modality:FINAL <> (a:kotlin.Function1<kotlin.Int, kotlin.Int>) returnType:kotlin.Unit
     VALUE_PARAMETER name:a index:0 type:kotlin.Function1<kotlin.Int, kotlin.Int>
     BLOCK_BODY