[IR Actualizer] Fix fake-override generation in actual A -> common B -> actual C hierarchy

...  where C defines a member x and A overrides the member x

#KT-61166 Fixed

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirLightTreeBlackBoxCodegenTestGenerated.java

@@ -33701,6 +33701,12 @@ public class FirLightTreeBlackBoxCodegenTestGenerated extends AbstractFirLightTr
             runTest("compiler/testData/codegen/box/multiplatform/kt60854.kt");
         }
 
+        @Test
+        @TestMetadata("kt61166.kt")
+        public void testKt61166() throws Exception {
+            runTest("compiler/testData/codegen/box/multiplatform/kt61166.kt");
+        }
+
         @Test
         @TestMetadata("noArgActualConstructor.kt")
         public void testNoArgActualConstructor() throws Exception {

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirPsiBlackBoxCodegenTestGenerated.java

@@ -33701,6 +33701,12 @@ public class FirPsiBlackBoxCodegenTestGenerated extends AbstractFirPsiBlackBoxCo
             runTest("compiler/testData/codegen/box/multiplatform/kt60854.kt");
         }
 
+        @Test
+        @TestMetadata("kt61166.kt")
+        public void testKt61166() throws Exception {
+            runTest("compiler/testData/codegen/box/multiplatform/kt61166.kt");
+        }
+
         @Test
         @TestMetadata("noArgActualConstructor.kt")
         public void testNoArgActualConstructor() throws Exception {

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

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.ir.IrBuiltIns
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.overrides.isOverridableByWithoutExternalConditions
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
 import org.jetbrains.kotlin.ir.types.IrTypeSystemContext
@@ -20,6 +21,7 @@ import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.resolve.OverridingUtil
 
 /**
  * It adds fake overrides to non-expect classes inside common or multi-platform module,
@@ -79,6 +81,32 @@ internal class ActualFakeOverridesAdder(
     ) {
         for (symbolFromSupertype in membersFromSupertype) {
             val memberFromSupertype = symbolFromSupertype.owner as IrDeclaration
+
+            if (memberFromSupertype is IrOverridableMember) {
+                // We can land here because of a hierarchy like
+                // actual A -> common B -> actual C
+                // where C defines a member x and A overrides the member x.
+                // We will first add a fake-override x to B and then land here.
+                // In this case we don't want to add a fake-override on top of the real override to A.
+                // Instead, we add the fake-override x to the overridden symbols of A.x.
+
+                @Suppress("UNCHECKED_CAST")
+                val override = klass.declarations.firstOrNull {
+                    it is IrOverridableMember &&
+                            typeSystemContext.isOverridableByWithoutExternalConditions(
+                                superMember = memberFromSupertype,
+                                subMember = it,
+                                checkIsInlineFlag = false,
+                                checkReturnType = false
+                            ).result == OverridingUtil.OverrideCompatibilityInfo.Result.OVERRIDABLE
+                } as? IrOverridableDeclaration<IrSymbol>
+
+                if (override != null) {
+                    override.overriddenSymbols += symbolFromSupertype
+                    continue
+                }
+            }
+
             val newMember = createFakeOverrideMember(listOf(memberFromSupertype), klass)
             val matchingFakeOverrides = collectActualCallablesMatchingToSpecificExpect(
                 newMember.symbol,

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/overrides/IrOverridingUtil.kt

@@ -627,11 +627,12 @@ class IrOverridingUtil(
         checkIsInlineFlag: Boolean,
         checkReturnType: Boolean
     ): OverrideCompatibilityInfo {
-        return isOverridableByWithoutExternalConditions(superMember, subMember, checkIsInlineFlag, checkReturnType)
+        return typeSystem.isOverridableByWithoutExternalConditions(superMember, subMember, checkIsInlineFlag, checkReturnType)
         // The frontend goes into external overridability condition details here, but don't deal with them in IR (yet?).
     }
+}
 
-    private fun isOverridableByWithoutExternalConditions(
+fun IrTypeSystemContext.isOverridableByWithoutExternalConditions(
     superMember: IrOverridableMember,
     subMember: IrOverridableMember,
     checkIsInlineFlag: Boolean,
@@ -695,7 +696,7 @@ class IrOverridingUtil(
 
     val typeCheckerState = createIrTypeCheckerState(
         IrTypeSystemContextWithAdditionalAxioms(
-                typeSystem,
+            this,
             superTypeParameters,
             subTypeParameters
         )
@@ -721,7 +722,6 @@ class IrOverridingUtil(
 
     return success()
 }
-}
 
 private val IrSimpleFunction?.hasExtensionReceiver: Boolean
     get() = this?.extensionReceiverParameter != null

compiler/testData/codegen/box/multiplatform/kt61166.kt

@@ -0,0 +1,26 @@
+// LANGUAGE: +MultiPlatformProjects
+// TARGET_BACKEND: JVM_IR
+// IGNORE_BACKEND_K1: ANY
+// ISSUE: KT-60854
+// WITH_STDLIB
+// FULL_JDK
+
+// MODULE: common
+// FILE: common.kt
+expect object A
+abstract class B : C()
+expect abstract class C()
+
+// MODULE: intermediate()()(common)
+// FILE: intermediate.kt
+actual object A : B() {
+    override val x: String get() = "OK"
+}
+
+actual abstract class C {
+    abstract val x: String
+}
+// MODULE: platform()()(intermediate)
+// FILE: platform.kt
+
+fun box(): String = A.x

compiler/testData/diagnostics/tests/multiplatform/manyImplMemberNotImplemented.fir.kt

@@ -9,7 +9,7 @@ expect open class C1()
 expect interface I1
 
 open class A : C1(), I1
-<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED{JVM}!>open class B : I1, C1()<!>
+open class B : I1, C1()
 
 expect abstract class C2()
 expect interface I2

compiler/testData/diagnostics/tests/multiplatform/manyInterfacesMemberNotImplemented.fir.kt

@@ -8,7 +8,7 @@
 expect interface S1
 expect interface S2
 
-<!MANY_INTERFACES_MEMBER_NOT_IMPLEMENTED{JVM}!>open class A : S1, S2<!>
+open class A : S1, S2
 
 class B : A()
 

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java

@@ -33701,6 +33701,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/multiplatform/kt60854.kt");
         }
 
+        @Test
+        @TestMetadata("kt61166.kt")
+        public void testKt61166() throws Exception {
+            runTest("compiler/testData/codegen/box/multiplatform/kt61166.kt");
+        }
+
         @Test
         @TestMetadata("noArgActualConstructor.kt")
         public void testNoArgActualConstructor() throws Exception {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenWithIrInlinerTestGenerated.java

@@ -33701,6 +33701,12 @@ public class IrBlackBoxCodegenWithIrInlinerTestGenerated extends AbstractIrBlack
             runTest("compiler/testData/codegen/box/multiplatform/kt60854.kt");
         }
 
+        @Test
+        @TestMetadata("kt61166.kt")
+        public void testKt61166() throws Exception {
+            runTest("compiler/testData/codegen/box/multiplatform/kt61166.kt");
+        }
+
         @Test
         @TestMetadata("noArgActualConstructor.kt")
         public void testNoArgActualConstructor() throws Exception {

compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -28702,6 +28702,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/multiplatform/kt60854.kt");
         }
 
+        @TestMetadata("kt61166.kt")
+        public void testKt61166() throws Exception {
+            runTest("compiler/testData/codegen/box/multiplatform/kt61166.kt");
+        }
+
         @TestMetadata("noArgActualConstructor.kt")
         public void testNoArgActualConstructor() throws Exception {
             runTest("compiler/testData/codegen/box/multiplatform/noArgActualConstructor.kt");