IR: keep flexible type annotations when building fake overrides

#KT-61751 Fixed

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

@@ -17,6 +17,8 @@ import org.jetbrains.kotlin.ir.types.impl.buildSimpleType
 import org.jetbrains.kotlin.ir.types.impl.makeTypeProjection
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
+import org.jetbrains.kotlin.name.StandardClassIds.Annotations.FlexibleNullability
+import org.jetbrains.kotlin.utils.addIfNotNull
 import org.jetbrains.kotlin.utils.memoryOptimizedMap
 
 // This is basically modelled after the inliner copier.
@@ -57,12 +59,27 @@ class CopyIrTreeWithSymbolsForFakeOverrides(
                     ?: argument
             }
 
+        private fun IrType.mergeTypeAnnotations(other: IrType): IrType {
+            // Flexible types are represented as a type annotation in IR, so we need to keep it when substituting type during override.
+            // Note that it's incorrect to merge _all_ type annotations though, because for a Collection subclass:
+            //
+            //     abstract class Z : Collection<Int>
+            //
+            // `Z.contains` should have the signature `(Int) -> Boolean`, NOT `(@UnsafeVariance Int) -> Boolean` which would occur if we
+            // copied all type annotations.
+            return addAnnotations(buildList {
+                for (fqName in TYPE_ANNOTATIONS_TO_MERGE) {
+                    addIfNotNull(other.annotations.findAnnotation(fqName))
+                }
+            })
+        }
+
         override fun remapType(type: IrType): IrType {
             if (type !is IrSimpleType) return type
 
             return when (val substitutedType = typeArguments[type.classifier]) {
                 is IrDynamicType -> substitutedType
-                is IrSimpleType -> substitutedType.mergeNullability(type)
+                is IrSimpleType -> substitutedType.mergeNullability(type).mergeTypeAnnotations(type)
                 else -> type.buildSimpleType {
                     kotlinType = null
                     classifier = symbolRemapper.getReferencedClassifier(type.classifier)
@@ -110,4 +127,11 @@ class CopyIrTreeWithSymbolsForFakeOverrides(
         parent,
         unimplementedOverridesStrategy
     )
+
+    private companion object {
+        // TODO: RawTypeAnnotation, FlexibleMutability, EnhancedNullability?
+        val TYPE_ANNOTATIONS_TO_MERGE = listOf(
+            FlexibleNullability.asSingleFqName(),
+        )
+    }
 }

compiler/testData/codegen/box/bridges/objectClone.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 
 import java.util.HashSet
 

compiler/testData/codegen/box/classes/inheritSetAndHashSet.kt

@@ -1,7 +1,6 @@
 // IGNORE_BACKEND: WASM
 // WASM_MUTE_REASON: STDLIB_COLLECTION_INHERITANCE
 // KJS_WITH_FULL_RUNTIME
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // DONT_TARGET_EXACT_BACKEND: NATIVE
 
 interface A : Set<String>

compiler/testData/codegen/box/collections/inheritFromAbstractMutableListInt.kt

@@ -1,5 +1,4 @@
 // WITH_STDLIB
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 
 abstract class A : AbstractMutableList<Int>()
 

compiler/testData/codegen/box/collections/noStubsInJavaSuperClass.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 
 // FILE: B.java
 public abstract class B<E> extends A<E> implements L<E> {

compiler/testData/codegen/box/collections/removeAtBridgeClashWithJava.kt

@@ -1,6 +1,5 @@
 // TARGET_BACKEND: JVM
 // WITH_STDLIB
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // FILE: removeAtBridgeClashWithJava.kt
 
 abstract class AJALI : JavaAbstractList<Int>()

compiler/testData/codegen/box/inlineArgsInPlace/arrayDequeRemoveAll.kt

@@ -1,5 +1,4 @@
 // WITH_STDLIB
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 
 @Suppress("INVISIBLE_MEMBER", "INVISIBLE_REFERENCE")
 class ArrayDeque<E> : AbstractMutableList<E> {

compiler/testData/codegen/box/jvm8/defaults/allCompatibility/bridgeWithJava.kt

@@ -1,6 +1,5 @@
 // !JVM_DEFAULT_MODE: all-compatibility
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // JVM_TARGET: 1.8
 // WITH_STDLIB
 // FULL_JDK

compiler/testData/codegen/box/jvm8/defaults/noDefaultImpls/bridgeWithJava.kt

@@ -1,6 +1,5 @@
 // !JVM_DEFAULT_MODE: all
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // JVM_TARGET: 1.8
 // WITH_STDLIB
 // FULL_JDK

compiler/testData/codegen/box/sam/partialSam.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // WITH_STDLIB
 // FILE: Fn.java
 public interface Fn<T, R> {

compiler/testData/codegen/box/sam/partialSamKT.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // WITH_STDLIB
 // FILE: Fn.java
 public interface Fn<T, R> {

compiler/testData/codegen/box/specialBuiltins/complexMapImpl.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // WITH_STDLIB
 
 // binary representation of fractional part of phi = (sqrt(5) - 1) / 2

compiler/testData/codegen/box/specialBuiltins/specialBridgeModality.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 
 import java.util.AbstractMap
 

compiler/testData/codegen/box/vararg/varargsOverride.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // MODULE: lib
 // FILE: A.java
 

compiler/testData/codegen/box/vararg/varargsOverride2.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 // MODULE: lib
 // FILE: A.java
 

compiler/testData/codegen/box/vararg/varargsOverride3.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_CODEGEN_WITH_IR_FAKE_OVERRIDE_GENERATION: KT-61751
 
 // MODULE: lib
 // FILE: A.java