[FIR] 2/2 Cleanup: drop no longer necessary FirActualCallableDeclarationChecker

It became possible to drop it after KT-62590. Now, on a frontend, the
return type check is part of a common AbstractExpectActualChecker logic

Change in nestedAnnotationClassViaActualTypealias.fir.kt aligns the
behaviour with K1. KT-61964

Review: https://jetbrains.team/p/kt/reviews/12750/timeline

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonDeclarationCheckers.kt

@@ -49,7 +49,6 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
             FirKClassWithIncorrectTypeArgumentChecker,
             FirImplicitNothingReturnTypeChecker,
             FirDynamicReceiverChecker,
-            FirActualCallableDeclarationChecker,
         )
 
     override val functionCheckers: Set<FirFunctionChecker>

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirActualCallableDeclarationChecker.kt

@@ -1,69 +0,0 @@
-/*
- * Copyright 2010-2023 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.analysis.checkers.declaration
-
-import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
-import org.jetbrains.kotlin.diagnostics.reportOn
-import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
-import org.jetbrains.kotlin.fir.analysis.checkers.getContainingClassSymbol
-import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
-import org.jetbrains.kotlin.fir.declarations.FirCallableDeclaration
-import org.jetbrains.kotlin.fir.declarations.expectForActual
-import org.jetbrains.kotlin.fir.declarations.getSingleExpectForActualOrNull
-import org.jetbrains.kotlin.fir.declarations.utils.isActual
-import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
-import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
-import org.jetbrains.kotlin.fir.types.areCompatibleExpectActualTypes
-import org.jetbrains.kotlin.fir.types.createExpectActualTypeParameterSubstitutor
-import org.jetbrains.kotlin.resolve.multiplatform.ExpectActualCompatibility
-import org.jetbrains.kotlin.resolve.multiplatform.ExpectActualMatchingCompatibility
-import org.jetbrains.kotlin.utils.zipIfSizesAreEqual
-
-object FirActualCallableDeclarationChecker : FirCallableDeclarationChecker() {
-    override fun check(declaration: FirCallableDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
-        if (!declaration.isActual) return
-
-        checkReturnTypes(declaration, context, reporter)
-    }
-
-    private fun checkReturnTypes(callableDeclaration: FirCallableDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
-        val actualFunctionSymbol = callableDeclaration.symbol
-        val expectFunctionSymbol = actualFunctionSymbol.getSingleExpectForActualOrNull() as? FirCallableSymbol ?: return
-
-        val expectTypeParameters = expectFunctionSymbol.getContainingClassSymbol(expectFunctionSymbol.moduleData.session)
-            ?.typeParameterSymbols.orEmpty()
-        val actualClassTypeParameters = actualFunctionSymbol.getContainingClassSymbol(context.session)?.typeParameterSymbols.orEmpty()
-
-        val parentSubstitutor = createExpectActualTypeParameterSubstitutor(
-            // It's responsibility of AbstractExpectActualCompatibilityChecker to report that
-            (expectTypeParameters zipIfSizesAreEqual actualClassTypeParameters) ?: return,
-            context.session
-        )
-
-        val substitutor = createExpectActualTypeParameterSubstitutor(
-            // It's responsibility of AbstractExpectActualCompatibilityChecker to check that
-            (expectFunctionSymbol.typeParameterSymbols zipIfSizesAreEqual actualFunctionSymbol.typeParameterSymbols) ?: return,
-            context.session,
-            parentSubstitutor
-        )
-
-        if (!areCompatibleExpectActualTypes(
-                substitutor.substituteOrSelf(expectFunctionSymbol.resolvedReturnType.type),
-                actualFunctionSymbol.resolvedReturnType.type,
-                context.session,
-                dynamicTypesEqualToAnything = false
-            )
-        ) {
-            reporter.reportOn(
-                callableDeclaration.source,
-                FirErrors.ACTUAL_WITHOUT_EXPECT,
-                actualFunctionSymbol,
-                actualFunctionSymbol.expectForActual as Map<ExpectActualMatchingCompatibility, Collection<FirBasedSymbol<*>>>,
-                context
-            )
-        }
-    }
-}

compiler/fir/providers/src/org/jetbrains/kotlin/fir/types/ExpectActualUtils.kt

@@ -10,7 +10,6 @@ import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
 import org.jetbrains.kotlin.fir.resolve.substitution.chain
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
-import org.jetbrains.kotlin.types.AbstractTypeChecker
 
 fun createExpectActualTypeParameterSubstitutor(
     expectActualTypeParameters: List<Pair<FirTypeParameterSymbol, FirTypeParameterSymbol>>,
@@ -29,28 +28,3 @@ fun createExpectActualTypeParameterSubstitutor(
     }
     return substitutor.chain(parentSubstitutor)
 }
-
-// Copy-pasted to org.jetbrains.kotlin.fir.resolve.transformers.mpp.FirExpectActualMatchingContextImpl.areCompatibleExpectActualTypes
-fun areCompatibleExpectActualTypes(
-    expectedType: ConeKotlinType?,
-    actualType: ConeKotlinType?,
-    actualSession: FirSession,
-    dynamicTypesEqualToAnything: Boolean = true
-): Boolean {
-    if (expectedType == null) return actualType == null
-    if (actualType == null) return false
-
-    if (!dynamicTypesEqualToAnything) {
-        val isExpectedDynamic = expectedType is ConeDynamicType
-        val isActualDynamic = actualType is ConeDynamicType
-        if (isExpectedDynamic && !isActualDynamic || !isExpectedDynamic && isActualDynamic) {
-            return false
-        }
-    }
-
-    return AbstractTypeChecker.equalTypes(
-        actualSession.typeContext,
-        expectedType,
-        actualType
-    )
-}

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/mpp/FirExpectActualMatchingContextImpl.kt

@@ -43,9 +43,6 @@ class FirExpectActualMatchingContextImpl private constructor(
     private val scopeSession: ScopeSession,
     private val allowedWritingMemberExpectForActualMapping: Boolean,
 ) : FirExpectActualMatchingContext, TypeSystemContext by actualSession.typeContext {
-    override val shouldCheckReturnTypesOfCallables: Boolean
-        get() = false
-
     override val shouldCheckAbsenceOfDefaultParamsInActual: Boolean
         get() = true
 
@@ -303,7 +300,6 @@ class FirExpectActualMatchingContextImpl private constructor(
     override val TypeParameterSymbolMarker.isReified: Boolean
         get() = asSymbol().isReified
 
-    // Copy-pasted to org.jetbrains.kotlin.fir.types.ExpectActualUtilsKt.areCompatibleExpectActualTypes
     override fun areCompatibleExpectActualTypes(
         expectType: KotlinTypeMarker?,
         actualType: KotlinTypeMarker?,

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/IrExpectActualMatchingContext.kt

@@ -92,9 +92,6 @@ internal abstract class IrExpectActualMatchingContext(
 
     private inline fun <reified T : IrDeclaration> DeclarationSymbolMarker.safeAsIr(): T? = (this as IrSymbol).owner as? T
 
-    override val shouldCheckReturnTypesOfCallables: Boolean
-        get() = true
-
     override val innerClassesCapturesOuterTypeParameters: Boolean
         get() = false
 

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/mpp/AbstractExpectActualChecker.kt

@@ -362,22 +362,20 @@ object AbstractExpectActualChecker {
         val expectedValueParameters = expectDeclaration.valueParameters
         val actualValueParameters = actualDeclaration.valueParameters
 
-        if (shouldCheckReturnTypesOfCallables) {
-            val substitutor = createExpectActualTypeParameterSubstitutor(
-                (expectedTypeParameters zipIfSizesAreEqual actualTypeParameters)
-                    ?: error("expect/actual type parameters sizes are checked earlier"),
-                parentSubstitutor
-            )
+        val substitutor = createExpectActualTypeParameterSubstitutor(
+            (expectedTypeParameters zipIfSizesAreEqual actualTypeParameters)
+                ?: error("expect/actual type parameters sizes are checked earlier"),
+            parentSubstitutor
+        )
 
-            if (!areCompatibleExpectActualTypes(
-                    substitutor.safeSubstitute(expectDeclaration.returnType),
-                    actualDeclaration.returnType,
-                    parameterOfAnnotationComparisonMode = insideAnnotationClass,
-                    dynamicTypesEqualToAnything = false
-                )
-            ) {
-                return ExpectActualCheckingCompatibility.ReturnType
-            }
+        if (!areCompatibleExpectActualTypes(
+                substitutor.safeSubstitute(expectDeclaration.returnType),
+                actualDeclaration.returnType,
+                parameterOfAnnotationComparisonMode = insideAnnotationClass,
+                dynamicTypesEqualToAnything = false
+            )
+        ) {
+            return ExpectActualCheckingCompatibility.ReturnType
         }
 
         if (actualDeclaration.hasStableParameterNames && !equalsBy(expectedValueParameters, actualValueParameters) { it.name }) {

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/mpp/ExpectActualMatchingContext.kt

@@ -20,8 +20,6 @@ import org.jetbrains.kotlin.types.model.TypeSubstitutorMarker
 import org.jetbrains.kotlin.types.model.TypeSystemContext
 
 interface ExpectActualMatchingContext<T : DeclarationSymbolMarker> : TypeSystemContext {
-    val shouldCheckReturnTypesOfCallables: Boolean
-
     /*
      * This flag indicates how are type parameters of inner classes stored in the specific implementation of RegularClassSymbolMarker
      *

compiler/testData/diagnostics/tests/multiplatform/defaultArguments/nestedAnnotationClassViaActualTypealias.fir.kt

@@ -11,4 +11,4 @@ class DefaultArgsInNestedClassImpl {
 }
 
 // Incompatible because of bug KT-31636
-actual typealias DefaultArgsInNestedClass = DefaultArgsInNestedClassImpl
+actual typealias <!NO_ACTUAL_CLASS_MEMBER_FOR_EXPECTED_CLASS!>DefaultArgsInNestedClass<!> = DefaultArgsInNestedClassImpl

compiler/testData/diagnostics/tests/multiplatform/hmpp/kt57320.fir.kt

@@ -34,7 +34,7 @@ interface KotlinXStringDemoInterface {
 // FILE: StringDemoInterface.kt
 actual typealias StringDemoInterface = KotlinXStringDemoInterface
 
-actual fun StringDemoIn<!EXPECT_ACTUAL_INCOMPATIBILITY!>terface.<!ACTUAL_WITHOUT_EXPECT("actual fun StringDemoInterface.plusK(): <ERROR TYPE REF: Unresolved name: value>; The following declaration is incompatible:    expect fun StringDemoInterface.plusK(): String")!>plusK<!>() = <!EXPECT_CLASS_AS_FUNCTION!>StringValue<!>(value).plus("K")<!>.<!UNRESOLVED_REFERENCE!>value<!>
+actual fun StringDemoIn<!EXPECT_ACTUAL_INCOMPATIBILITY!>terface.<!ACTUAL_WITHOUT_EXPECT("actual fun StringDemoInterface.plusK(): <ERROR TYPE REF: Unresolved name: value>; The following declaration is incompatible because return type is different:    expect fun StringDemoInterface.plusK(): String")!>plusK<!>() = <!EXPECT_CLASS_AS_FUNCTION!>StringValue<!>(value).plus("K")<!>.<!UNRESOLVED_REFERENCE!>value<!>
 
 // FILE: main.kt
 class StringDemo(override val value: String) : StringDemoInterface

compiler/testData/multiplatform/classScopes/functionIncorrectSignature/output.txt

@@ -6,7 +6,7 @@ Output:
 Exit code: COMPILATION_ERROR
 Output:
 compiler/testData/multiplatform/classScopes/functionIncorrectSignature/jvm.kt:2:16: error: 'actual fun function(b: ByteArray): Long' has no corresponding expected declaration
-The following declaration is incompatible:
+The following declaration is incompatible because return type is different:
     expect fun function(b: ByteArray): Int
 
     actual fun function(b: ByteArray): Long = b.size.toLong()

compiler/testData/multiplatform/classScopes/functionIncorrectSignatureFromSuperclass/output.txt

@@ -5,9 +5,12 @@ Output:
 -- JVM --
 Exit code: COMPILATION_ERROR
 Output:
-compiler/testData/multiplatform/classScopes/functionIncorrectSignatureFromSuperclass/common.kt:1:1: error: expect declaration `Foo` doesn't match actual `Foo` because some expected members have no actual ones
-expect class Foo {
-^
-compiler/testData/multiplatform/classScopes/functionIncorrectSignatureFromSuperclass/common.kt:2:5: error: expect declaration `function` doesn't match actual `function` because return type is different
-    fun function(b: ByteArray): Int
-    ^
+compiler/testData/multiplatform/classScopes/functionIncorrectSignatureFromSuperclass/jvm.kt:5:14: error: 'actual class Foo : Base' has no corresponding members for expected class members:
+
+    expect fun function(b: ByteArray): Int
+
+    The following declaration is incompatible because return type is different:
+        fun function(b: ByteArray): Long
+
+actual class Foo : Base()
+             ^

compiler/testData/multiplatform/incompatibleCallables/output.txt

@@ -6,7 +6,7 @@ Output:
 Exit code: COMPILATION_ERROR
 Output:
 compiler/testData/multiplatform/incompatibleCallables/jvm.kt:1:12: error: 'actual fun f1(): String' has no corresponding expected declaration
-The following declaration is incompatible:
+The following declaration is incompatible because return type is different:
     expect fun f1(): Unit
 
 actual fun f1(): String = ""