[FIR2IR] Generate @FlexibleMutability annotation on IR types if needed

compiler/fir/fir2ir/jvm-backend/src/org/jetbrains/kotlin/fir/backend/jvm/Fir2IrJvmSpecialAnnotationSymbolProvider.kt

@@ -40,6 +40,7 @@ class Fir2IrJvmSpecialAnnotationSymbolProvider : Fir2IrSpecialSymbolProvider() {
         when (id) {
             ENHANCED_NULLABILITY_ID -> id.toIrClass(kotlinJvmInternalPackage).symbol
             FLEXIBLE_NULLABILITY_ID -> id.toIrClass(kotlinInternalIrPackage).symbol
+            FLEXIBLE_MUTABILITY_ID -> id.toIrClass(kotlinInternalIrPackage).symbol
             RAW_TYPE_ANNOTATION_ID -> id.toIrClass(kotlinInternalIrPackage).symbol
             else -> null
         }
@@ -60,7 +61,9 @@ class Fir2IrJvmSpecialAnnotationSymbolProvider : Fir2IrSpecialSymbolProvider() {
         private val ENHANCED_NULLABILITY_ID = ClassId.topLevel(JvmAnnotationNames.ENHANCED_NULLABILITY_ANNOTATION)
         private val FLEXIBLE_NULLABILITY_ID =
             ClassId.topLevel(IrBuiltIns.KOTLIN_INTERNAL_IR_FQN.child(Name.identifier("FlexibleNullability")))
+        private val FLEXIBLE_MUTABILITY_ID =
+            ClassId.topLevel(IrBuiltIns.KOTLIN_INTERNAL_IR_FQN.child(Name.identifier("FlexibleMutability")))
         private val RAW_TYPE_ANNOTATION_ID =
             ClassId.topLevel(IrBuiltIns.KOTLIN_INTERNAL_IR_FQN.child(Name.identifier("RawType")))
     }
-}
+}

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrBuiltIns.kt

@@ -42,6 +42,13 @@ class Fir2IrBuiltIns(
     internal fun flexibleNullabilityAnnotationConstructorCall(): IrConstructorCall? =
         flexibleNullabilityAnnotationSymbol?.toConstructorCall()
 
+    private val flexibleMutabilityAnnotationSymbol by lazy {
+        specialAnnotationIrSymbolById(StandardClassIds.Annotations.FlexibleMutability)
+    }
+
+    internal fun flexibleMutabilityAnnotationConstructorCall(): IrConstructorCall? =
+        flexibleMutabilityAnnotationSymbol?.toConstructorCall()
+
     private val rawTypeAnnotationSymbol by lazy {
         specialAnnotationIrSymbolById(StandardClassIds.Annotations.RawTypeAnnotation)
     }

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrTypeConverter.kt

@@ -28,6 +28,7 @@ import org.jetbrains.kotlin.ir.types.makeNotNull
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.StandardClassIds
 import org.jetbrains.kotlin.name.StandardClassIds.Annotations.ExtensionFunctionType
+import org.jetbrains.kotlin.types.CommonFlexibleTypeBoundsChecker
 import org.jetbrains.kotlin.types.TypeApproximatorConfiguration
 import org.jetbrains.kotlin.types.Variance
 
@@ -109,6 +110,7 @@ class Fir2IrTypeConverter(
         typeContext: ConversionTypeContext = ConversionTypeContext.DEFAULT,
         annotations: List<FirAnnotation> = emptyList(),
         hasFlexibleNullability: Boolean = false,
+        hasFlexibleMutability: Boolean = false,
         addRawTypeAnnotation: Boolean = false
     ): IrType {
         return when (this) {
@@ -137,6 +139,11 @@ class Fir2IrTypeConverter(
                         }
                     }
                 }
+                if (hasFlexibleMutability) {
+                    builtIns.flexibleMutabilityAnnotationConstructorCall()?.let {
+                        typeAnnotations += it
+                    }
+                }
 
                 if (isExtensionFunctionType && annotations.getAnnotationsByClassId(ExtensionFunctionType, session).isEmpty()) {
                     builtIns.extensionFunctionTypeAnnotationConstructorCall()?.let {
@@ -173,6 +180,7 @@ class Fir2IrTypeConverter(
                     typeContext,
                     annotations,
                     hasFlexibleNullability = lowerBound.nullability != upperBound.nullability,
+                    hasFlexibleMutability = isMutabilityFlexible(),
                     addRawTypeAnnotation = true
                 )
             }
@@ -190,10 +198,18 @@ class Fir2IrTypeConverter(
                     (intermediate.withNullability(upper.isNullable) as ConeKotlinType)
                         .withAttributes(lower.attributes)
                         .toIrType(
-                            typeContext, annotations, hasFlexibleNullability = lower.nullability != upper.nullability
+                            typeContext,
+                            annotations,
+                            hasFlexibleNullability = lower.nullability != upper.nullability,
+                            hasFlexibleMutability = isMutabilityFlexible()
                         )
                 } else {
-                    upperBound.toIrType(typeContext, annotations, hasFlexibleNullability = lowerBound.nullability != upperBound.nullability)
+                    upperBound.toIrType(
+                        typeContext,
+                        annotations,
+                        hasFlexibleNullability = lowerBound.nullability != upperBound.nullability,
+                        hasFlexibleMutability = isMutabilityFlexible()
+                    )
                 }
             }
             is ConeCapturedType -> {
@@ -226,6 +242,14 @@ class Fir2IrTypeConverter(
         }
     }
 
+    private fun ConeFlexibleType.isMutabilityFlexible(): Boolean {
+        val lowerFqName = lowerBound.classId?.asSingleFqName() ?: return false
+        val upperFqName = upperBound.classId?.asSingleFqName() ?: return false
+        if (lowerFqName == upperFqName) return false
+        return CommonFlexibleTypeBoundsChecker.getBaseBoundFqNameByMutability(lowerFqName) ==
+                CommonFlexibleTypeBoundsChecker.getBaseBoundFqNameByMutability(upperFqName)
+    }
+
     private fun ConeTypeProjection.toIrTypeArgument(typeContext: ConversionTypeContext): IrTypeArgument {
         fun toIrTypeArgument(type: ConeKotlinType, variance: Variance): IrTypeProjection {
             val irType = type.toIrType(typeContext)

compiler/testData/codegen/box/reflection/typeOf/flexibleTypes_after.kt

@@ -1,6 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_BACKEND_K2: JVM_IR, JS_IR
-// FIR status: Fail 2: kotlin.collections.List<kotlin.String!>
 // WITH_REFLECT
 // FILE: box.kt
 

compiler/testData/codegen/box/reflection/typeOf/rawTypes_after.kt

@@ -1,6 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_BACKEND_K2: JVM_IR, JS_IR
-// FIR status: Fail 3: (kotlin.collections.MutableList<kotlin.Any?>..kotlin.collections.MutableList<*>?)
 // WITH_REFLECT
 // FILE: box.kt
 

compiler/testData/ir/irText/classes/kt45934.fir.ir.txt

@@ -6,14 +6,14 @@ FILE fqName:<root> fileName:/kt45934.kt
       BLOCK_BODY
         DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:C modality:FINAL visibility:public superTypes:[<root>.I]'
-    FUN DELEGATED_MEMBER name:foo visibility:public modality:OPEN <C> ($this:<root>.C) returnType:@[FlexibleNullability] kotlin.collections.MutableList<@[FlexibleNullability] C of <root>.C.foo?>?
+    FUN DELEGATED_MEMBER name:foo visibility:public modality:OPEN <C> ($this:<root>.C) returnType:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] C of <root>.C.foo?>?
       overridden:
-        public abstract fun foo <C> (): @[FlexibleNullability] kotlin.collections.MutableList<@[FlexibleNullability] C of <root>.I.foo?>? declared in <root>.I
+        public abstract fun foo <C> (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] C of <root>.I.foo?>? declared in <root>.I
       TYPE_PARAMETER name:C index:0 variance: superTypes:[@[FlexibleNullability] kotlin.Any?] reified:false
       $this: VALUE_PARAMETER name:<this> type:<root>.C
       BLOCK_BODY
-        RETURN type=kotlin.Nothing from='public open fun foo <C> (): @[FlexibleNullability] kotlin.collections.MutableList<@[FlexibleNullability] C of <root>.C.foo?>? declared in <root>.C'
-          CALL 'public open fun foo (): @[FlexibleNullability] kotlin.collections.MutableList<@[FlexibleNullability] kotlin.String?>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableList<@[FlexibleNullability] kotlin.String?>? origin=null
+        RETURN type=kotlin.Nothing from='public open fun foo <C> (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] C of <root>.C.foo?>? declared in <root>.C'
+          CALL 'public open fun foo (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] kotlin.String?>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] kotlin.String?>? origin=null
             $this: GET_FIELD 'FIELD DELEGATE name:$$delegate_0 type:<root>.J visibility:private [final]' type=<root>.J origin=null
               receiver: GET_VAR '<this>: <root>.C declared in <root>.C.foo' type=<root>.C origin=null
     FIELD DELEGATE name:$$delegate_0 type:<root>.J visibility:private [final]

compiler/testData/ir/irText/firProblems/AbstractMutableMap.fir.ir.txt

@@ -20,11 +20,11 @@ FILE fqName:<root> fileName:/AbstractMutableMap.kt
           CONST Null type=kotlin.Nothing? value=null
     PROPERTY name:entries visibility:public modality:OPEN [val]
       overridden:
-        public abstract entries: @[FlexibleNullability] kotlin.collections.MutableSet<@[FlexibleNullability] kotlin.collections.MutableMap.MutableEntry<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?, @[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>?>? [fake_override,val]
+        public abstract entries: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableSet<@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableMap.MutableEntry<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?, @[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>?>? [fake_override,val]
       FUN name:<get-entries> visibility:public modality:OPEN <> ($this:<root>.MyMap<K of <root>.MyMap, V of <root>.MyMap>) returnType:kotlin.collections.MutableSet<kotlin.collections.MutableMap.MutableEntry<K of <root>.MyMap, V of <root>.MyMap>>
         correspondingProperty: PROPERTY name:entries visibility:public modality:OPEN [val]
         overridden:
-          public abstract fun <get-entries> (): @[FlexibleNullability] kotlin.collections.MutableSet<@[FlexibleNullability] kotlin.collections.MutableMap.MutableEntry<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?, @[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>?>? [fake_override] declared in kotlin.collections.AbstractMutableMap
+          public abstract fun <get-entries> (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableSet<@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableMap.MutableEntry<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?, @[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>?>? [fake_override] declared in kotlin.collections.AbstractMutableMap
         $this: VALUE_PARAMETER name:<this> type:<root>.MyMap<K of <root>.MyMap, V of <root>.MyMap>
         BLOCK_BODY
           RETURN type=kotlin.Nothing from='public open fun <get-entries> (): kotlin.collections.MutableSet<kotlin.collections.MutableMap.MutableEntry<K of <root>.MyMap, V of <root>.MyMap>> declared in <root>.MyMap'
@@ -55,19 +55,19 @@ FILE fqName:<root> fileName:/AbstractMutableMap.kt
       VALUE_PARAMETER name:value index:1 type:V of <root>.MyMap
     PROPERTY FAKE_OVERRIDE name:keys visibility:public modality:OPEN [fake_override,val]
       overridden:
-        public open keys: @[FlexibleNullability] kotlin.collections.MutableSet<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?>? [fake_override,val]
-      FUN FAKE_OVERRIDE name:<get-keys> visibility:public modality:OPEN <> ($this:java.util.AbstractMap<K of java.util.AbstractMap, V of java.util.AbstractMap>) returnType:@[FlexibleNullability] kotlin.collections.MutableSet<@[FlexibleNullability] K of <root>.MyMap?>? [fake_override]
+        public open keys: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableSet<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?>? [fake_override,val]
+      FUN FAKE_OVERRIDE name:<get-keys> visibility:public modality:OPEN <> ($this:java.util.AbstractMap<K of java.util.AbstractMap, V of java.util.AbstractMap>) returnType:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableSet<@[FlexibleNullability] K of <root>.MyMap?>? [fake_override]
         correspondingProperty: PROPERTY FAKE_OVERRIDE name:keys visibility:public modality:OPEN [fake_override,val]
         overridden:
-          public open fun <get-keys> (): @[FlexibleNullability] kotlin.collections.MutableSet<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?>? [fake_override] declared in kotlin.collections.AbstractMutableMap
+          public open fun <get-keys> (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableSet<@[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?>? [fake_override] declared in kotlin.collections.AbstractMutableMap
         $this: VALUE_PARAMETER name:<this> type:java.util.AbstractMap<K of java.util.AbstractMap, V of java.util.AbstractMap>
     PROPERTY FAKE_OVERRIDE name:values visibility:public modality:OPEN [fake_override,val]
       overridden:
-        public open values: @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>? [fake_override,val]
-      FUN FAKE_OVERRIDE name:<get-values> visibility:public modality:OPEN <> ($this:java.util.AbstractMap<K of java.util.AbstractMap, V of java.util.AbstractMap>) returnType:@[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] V of <root>.MyMap?>? [fake_override]
+        public open values: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>? [fake_override,val]
+      FUN FAKE_OVERRIDE name:<get-values> visibility:public modality:OPEN <> ($this:java.util.AbstractMap<K of java.util.AbstractMap, V of java.util.AbstractMap>) returnType:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] V of <root>.MyMap?>? [fake_override]
         correspondingProperty: PROPERTY FAKE_OVERRIDE name:values visibility:public modality:OPEN [fake_override,val]
         overridden:
-          public open fun <get-values> (): @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>? [fake_override] declared in kotlin.collections.AbstractMutableMap
+          public open fun <get-values> (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?>? [fake_override] declared in kotlin.collections.AbstractMutableMap
         $this: VALUE_PARAMETER name:<this> type:java.util.AbstractMap<K of java.util.AbstractMap, V of java.util.AbstractMap>
     FUN FAKE_OVERRIDE name:replaceAll visibility:public modality:OPEN <> ($this:kotlin.collections.MutableMap<K of kotlin.collections.MutableMap, V of kotlin.collections.MutableMap>, p0:@[EnhancedNullability] java.util.function.BiFunction<in @[EnhancedNullability] K of <root>.MyMap, in @[EnhancedNullability] V of <root>.MyMap, out @[EnhancedNullability] V of <root>.MyMap>) returnType:kotlin.Unit [fake_override]
       overridden:

compiler/testData/ir/irText/firProblems/AllCandidates.fir.ir.txt

@@ -63,7 +63,7 @@ FILE fqName:<root> fileName:/AllCandidates.kt
             FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> ($receiver:@[FlexibleNullability] <root>.OverloadResolutionResultsImpl<@[FlexibleNullability] A of <root>.allCandidatesResult?>?) returnType:kotlin.Unit
               $receiver: VALUE_PARAMETER name:$this$apply type:@[FlexibleNullability] <root>.OverloadResolutionResultsImpl<@[FlexibleNullability] A of <root>.allCandidatesResult?>?
               BLOCK_BODY
-                CALL 'public open fun setAllCandidates (allCandidates: @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] <root>.ResolvedCall<@[FlexibleNullability] D of <root>.OverloadResolutionResultsImpl?>?>?): kotlin.Unit declared in <root>.OverloadResolutionResultsImpl' type=kotlin.Unit origin=EQ
+                CALL 'public open fun setAllCandidates (allCandidates: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] <root>.ResolvedCall<@[FlexibleNullability] D of <root>.OverloadResolutionResultsImpl?>?>?): kotlin.Unit declared in <root>.OverloadResolutionResultsImpl' type=kotlin.Unit origin=EQ
                   $this: GET_VAR '$this$apply: @[FlexibleNullability] <root>.OverloadResolutionResultsImpl<@[FlexibleNullability] A of <root>.allCandidatesResult?>? declared in <root>.allCandidatesResult.<anonymous>' type=@[FlexibleNullability] <root>.OverloadResolutionResultsImpl<@[FlexibleNullability] A of <root>.allCandidatesResult?>? origin=null
                   allCandidates: CALL 'public final fun map <T, R> (transform: kotlin.Function1<T of kotlin.collections.CollectionsKt.map, R of kotlin.collections.CollectionsKt.map>): kotlin.collections.List<R of kotlin.collections.CollectionsKt.map> [inline] declared in kotlin.collections.CollectionsKt' type=kotlin.collections.List<<root>.ResolvedCall<A of <root>.allCandidatesResult>> origin=null
                     <T>: <root>.MyCandidate

compiler/testData/ir/irText/firProblems/SyntheticSetterType.fir.ir.txt

@@ -1,8 +0,0 @@
-FILE fqName:<root> fileName:/SyntheticSetterType.kt
-  FUN name:foo visibility:public modality:FINAL <> (descriptor:<root>.PropertyDescriptorImpl) returnType:kotlin.Unit
-    VALUE_PARAMETER name:descriptor index:0 type:<root>.PropertyDescriptorImpl
-    BLOCK_BODY
-      CALL 'public open fun setOverriddenDescriptors (overriddenDescriptors: @[EnhancedNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] <root>.CallableMemberDescriptor?>): kotlin.Unit declared in <root>.PropertyDescriptorImpl' type=kotlin.Unit origin=EQ
-        $this: GET_VAR 'descriptor: <root>.PropertyDescriptorImpl declared in <root>.foo' type=<root>.PropertyDescriptorImpl origin=null
-        overriddenDescriptors: CALL 'public final fun emptyList <T> (): kotlin.collections.List<T of kotlin.collections.CollectionsKt.emptyList> declared in kotlin.collections.CollectionsKt' type=kotlin.collections.List<@[FlexibleNullability] <root>.PropertyDescriptor?> origin=null
-          <T>: @[FlexibleNullability] <root>.PropertyDescriptor?

compiler/testData/ir/irText/firProblems/SyntheticSetterType.fir.kt.txt

@@ -1,3 +0,0 @@
-fun foo(descriptor: PropertyDescriptorImpl) {
-  descriptor.setOverriddenDescriptors(overriddenDescriptors = emptyList<@FlexibleNullability PropertyDescriptor?>())
-}

compiler/testData/ir/irText/firProblems/SyntheticSetterType.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // TARGET_BACKEND: JVM
 // WITH_STDLIB
 // FILE: PropertyDescriptorImpl.java

compiler/testData/ir/irText/regressions/typeParametersInImplicitCast.fir.ir.txt

@@ -13,7 +13,7 @@ FILE fqName:<root> fileName:/typeParametersInImplicitCast.kt
               VALUE_PARAMETER name:it index:0 type:kotlin.collections.List<T of <root>.problematic>
               BLOCK_BODY
                 RETURN type=kotlin.Nothing from='local final fun <anonymous> (it: kotlin.collections.List<T of <root>.problematic>): kotlin.collections.Iterable<@[FlexibleNullability] T of <root>.problematic?> declared in <root>.problematic'
-                  TYPE_OP type=kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.problematic?> origin=IMPLICIT_NOTNULL typeOperand=kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.problematic?>
-                    CALL 'public/*package*/ open fun id <T> (v: @[FlexibleNullability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.ListId.id?>?): @[EnhancedNullability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.ListId.id?> declared in <root>.ListId' type=@[EnhancedNullability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.problematic?> origin=null
+                  TYPE_OP type=@[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.problematic?> origin=IMPLICIT_NOTNULL typeOperand=@[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.problematic?>
+                    CALL 'public/*package*/ open fun id <T> (v: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.ListId.id?>?): @[EnhancedNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.ListId.id?> declared in <root>.ListId' type=@[EnhancedNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[FlexibleNullability] T of <root>.problematic?> origin=null
                       <T>: @[FlexibleNullability] T of <root>.problematic?
                       v: GET_VAR 'it: kotlin.collections.List<T of <root>.problematic> declared in <root>.problematic.<anonymous>' type=kotlin.collections.List<T of <root>.problematic> origin=null

compiler/testData/ir/irText/regressions/typeParametersInImplicitCast.fir.kt.txt

@@ -1,6 +1,6 @@
 fun <T : Any?> problematic(lss: List<List<T>>): List<T> {
   return lss.flatMap<List<T>, @FlexibleNullability T?>(transform = local fun <anonymous>(it: List<T>): Iterable<@FlexibleNullability T?> {
-    return id<@FlexibleNullability T?>(v = it) /*!! MutableList<@FlexibleNullability T?> */
+    return id<@FlexibleNullability T?>(v = it) /*!! @FlexibleMutability MutableList<@FlexibleNullability T?> */
   }
 )
 }

compiler/testData/ir/irText/stubs/builtinMap.fir.ir.txt

@@ -18,7 +18,7 @@ FILE fqName:<root> fileName:/builtinMap.kt
             if: CONST Boolean type=kotlin.Boolean value=true
             then: CALL 'public final fun apply <T> (block: @[ExtensionFunctionType] kotlin.Function1<T of kotlin.StandardKt.apply, kotlin.Unit>): T of kotlin.StandardKt.apply [inline] declared in kotlin.StandardKt' type=java.util.LinkedHashMap<@[FlexibleNullability] K1 of <root>.plus?, @[FlexibleNullability] V1 of <root>.plus?> origin=null
               <T>: java.util.LinkedHashMap<@[FlexibleNullability] K1 of <root>.plus?, @[FlexibleNullability] V1 of <root>.plus?>
-              $receiver: CONSTRUCTOR_CALL 'public constructor <init> (p0: @[FlexibleNullability] kotlin.collections.MutableMap<out @[FlexibleNullability] K of java.util.LinkedHashMap?, out @[FlexibleNullability] V of java.util.LinkedHashMap?>?) declared in java.util.LinkedHashMap' type=java.util.LinkedHashMap<@[FlexibleNullability] K1 of <root>.plus?, @[FlexibleNullability] V1 of <root>.plus?> origin=null
+              $receiver: CONSTRUCTOR_CALL 'public constructor <init> (p0: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableMap<out @[FlexibleNullability] K of java.util.LinkedHashMap?, out @[FlexibleNullability] V of java.util.LinkedHashMap?>?) declared in java.util.LinkedHashMap' type=java.util.LinkedHashMap<@[FlexibleNullability] K1 of <root>.plus?, @[FlexibleNullability] V1 of <root>.plus?> origin=null
                 <class: K>: @[FlexibleNullability] K1 of <root>.plus?
                 <class: V>: @[FlexibleNullability] V1 of <root>.plus?
                 p0: GET_VAR '<this>: kotlin.collections.Map<out K1 of <root>.plus, V1 of <root>.plus> declared in <root>.plus' type=kotlin.collections.Map<out K1 of <root>.plus, V1 of <root>.plus> origin=null

compiler/testData/ir/irText/types/javaWildcardType.fir.ir.txt

@@ -32,44 +32,44 @@ FILE fqName:<root> fileName:/javaWildcardType.kt
       BLOCK_BODY
         DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:C modality:FINAL visibility:public superTypes:[<root>.J; <root>.K]'
-    FUN DELEGATED_MEMBER name:jf1 visibility:public modality:OPEN <> ($this:<root>.C) returnType:@[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?
+    FUN DELEGATED_MEMBER name:jf1 visibility:public modality:OPEN <> ($this:<root>.C) returnType:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?
       overridden:
-        public abstract fun jf1 (): @[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J
+        public abstract fun jf1 (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J
       $this: VALUE_PARAMETER name:<this> type:<root>.C
       BLOCK_BODY
-        RETURN type=kotlin.Nothing from='public open fun jf1 (): @[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C'
-          CALL 'public abstract fun jf1 (): @[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? origin=null
+        RETURN type=kotlin.Nothing from='public open fun jf1 (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C'
+          CALL 'public abstract fun jf1 (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? origin=null
             $this: GET_FIELD 'FIELD DELEGATE name:$$delegate_0 type:<root>.J visibility:private [final]' type=<root>.J origin=null
               receiver: GET_VAR '<this>: <root>.C declared in <root>.C.jf1' type=<root>.C origin=null
-    FUN DELEGATED_MEMBER name:jf2 visibility:public modality:OPEN <> ($this:<root>.C) returnType:@[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?
+    FUN DELEGATED_MEMBER name:jf2 visibility:public modality:OPEN <> ($this:<root>.C) returnType:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?
       overridden:
-        public abstract fun jf2 (): @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J
+        public abstract fun jf2 (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J
       $this: VALUE_PARAMETER name:<this> type:<root>.C
       BLOCK_BODY
-        RETURN type=kotlin.Nothing from='public open fun jf2 (): @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C'
-          CALL 'public abstract fun jf2 (): @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? origin=null
+        RETURN type=kotlin.Nothing from='public open fun jf2 (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C'
+          CALL 'public abstract fun jf2 (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? origin=null
             $this: GET_FIELD 'FIELD DELEGATE name:$$delegate_0 type:<root>.J visibility:private [final]' type=<root>.J origin=null
               receiver: GET_VAR '<this>: <root>.C declared in <root>.C.jf2' type=<root>.C origin=null
-    FUN DELEGATED_MEMBER name:jg1 visibility:public modality:OPEN <> ($this:<root>.C, c:@[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?) returnType:kotlin.Unit
+    FUN DELEGATED_MEMBER name:jg1 visibility:public modality:OPEN <> ($this:<root>.C, c:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?) returnType:kotlin.Unit
       overridden:
-        public abstract fun jg1 (c: @[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J
+        public abstract fun jg1 (c: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J
       $this: VALUE_PARAMETER name:<this> type:<root>.C
-      VALUE_PARAMETER name:c index:0 type:@[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?
+      VALUE_PARAMETER name:c index:0 type:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?
       BLOCK_BODY
-        CALL 'public abstract fun jg1 (c: @[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
+        CALL 'public abstract fun jg1 (c: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
           $this: GET_FIELD 'FIELD DELEGATE name:$$delegate_0 type:<root>.J visibility:private [final]' type=<root>.J origin=null
             receiver: GET_VAR '<this>: <root>.C declared in <root>.C.jg1' type=<root>.C origin=null
-          c: GET_VAR 'c: @[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C.jg1' type=@[FlexibleNullability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? origin=null
-    FUN DELEGATED_MEMBER name:jg2 visibility:public modality:OPEN <> ($this:<root>.C, c:@[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?) returnType:kotlin.Unit
+          c: GET_VAR 'c: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C.jg1' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<out @[FlexibleNullability] kotlin.CharSequence?>? origin=null
+    FUN DELEGATED_MEMBER name:jg2 visibility:public modality:OPEN <> ($this:<root>.C, c:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?) returnType:kotlin.Unit
       overridden:
-        public abstract fun jg2 (c: @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J
+        public abstract fun jg2 (c: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J
       $this: VALUE_PARAMETER name:<this> type:<root>.C
-      VALUE_PARAMETER name:c index:0 type:@[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?
+      VALUE_PARAMETER name:c index:0 type:@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?
       BLOCK_BODY
-        CALL 'public abstract fun jg2 (c: @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
+        CALL 'public abstract fun jg2 (c: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
           $this: GET_FIELD 'FIELD DELEGATE name:$$delegate_0 type:<root>.J visibility:private [final]' type=<root>.J origin=null
             receiver: GET_VAR '<this>: <root>.C declared in <root>.C.jg2' type=<root>.C origin=null
-          c: GET_VAR 'c: @[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C.jg2' type=@[FlexibleNullability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? origin=null
+          c: GET_VAR 'c: @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? declared in <root>.C.jg2' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableCollection<@[FlexibleNullability] kotlin.CharSequence?>? origin=null
     FIELD DELEGATE name:$$delegate_0 type:<root>.J visibility:private [final]
       EXPRESSION_BODY
         GET_VAR 'j: <root>.J declared in <root>.C.<init>' type=<root>.J origin=null

compiler/testData/ir/irText/types/javaWildcardType.fir.kt.txt

@@ -16,19 +16,19 @@ class C : J, K {
 
   }
 
-  override fun jf1(): @FlexibleNullability MutableCollection<out @FlexibleNullability CharSequence?>? {
+  override fun jf1(): @FlexibleNullability @FlexibleMutability MutableCollection<out @FlexibleNullability CharSequence?>? {
     return <this>.#$$delegate_0.jf1()
   }
 
-  override fun jf2(): @FlexibleNullability MutableCollection<@FlexibleNullability CharSequence?>? {
+  override fun jf2(): @FlexibleNullability @FlexibleMutability MutableCollection<@FlexibleNullability CharSequence?>? {
     return <this>.#$$delegate_0.jf2()
   }
 
-  override fun jg1(c: @FlexibleNullability MutableCollection<out @FlexibleNullability CharSequence?>?) {
+  override fun jg1(c: @FlexibleNullability @FlexibleMutability MutableCollection<out @FlexibleNullability CharSequence?>?) {
     <this>.#$$delegate_0.jg1(c = c)
   }
 
-  override fun jg2(c: @FlexibleNullability MutableCollection<@FlexibleNullability CharSequence?>?) {
+  override fun jg2(c: @FlexibleNullability @FlexibleMutability MutableCollection<@FlexibleNullability CharSequence?>?) {
     <this>.#$$delegate_0.jg2(c = c)
   }
 

compiler/testData/ir/irText/types/nullChecks/enhancedNullabilityInDestructuringAssignment.fir.ir.txt

@@ -182,8 +182,8 @@ FILE fqName:<root> fileName:/enhancedNullabilityInDestructuringAssignment.kt
           <T>: kotlin.collections.IndexedValue<@[EnhancedNullability] <root>.P>
           $receiver: CALL 'public final fun withIndex <T> (): kotlin.collections.Iterable<kotlin.collections.IndexedValue<T of kotlin.collections.CollectionsKt.withIndex>> declared in kotlin.collections.CollectionsKt' type=kotlin.collections.Iterable<kotlin.collections.IndexedValue<@[EnhancedNullability] <root>.P>> origin=null
             <T>: @[EnhancedNullability] <root>.P
-            $receiver: TYPE_OP type=kotlin.collections.MutableList<@[EnhancedNullability] <root>.P> origin=IMPLICIT_NOTNULL typeOperand=kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>
-              CALL 'public open fun listOfNotNull (): @[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? origin=null
+            $receiver: TYPE_OP type=@[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P> origin=IMPLICIT_NOTNULL typeOperand=@[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>
+              CALL 'public open fun listOfNotNull (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? origin=null
       VAR name:x type:kotlin.Int [val]
         CALL 'public final fun component1 (): kotlin.Int [operator] declared in kotlin.collections.IndexedValue' type=kotlin.Int origin=COMPONENT_N(index=1)
           $this: GET_VAR 'val tmp_3: kotlin.collections.IndexedValue<@[EnhancedNullability] <root>.P> [val] declared in <root>.test4' type=kotlin.collections.IndexedValue<@[EnhancedNullability] <root>.P> origin=null

compiler/testData/ir/irText/types/nullChecks/enhancedNullabilityInDestructuringAssignment.fir.kt.txt

@@ -80,7 +80,7 @@ fun test3() {
 }
 
 fun test4() {
-  val <destruct>: IndexedValue<@EnhancedNullability P> = listOfNotNull() /*!! MutableList<@EnhancedNullability P> */.withIndex<@EnhancedNullability P>().first<IndexedValue<@EnhancedNullability P>>()
+  val <destruct>: IndexedValue<@EnhancedNullability P> = listOfNotNull() /*!! @FlexibleMutability MutableList<@EnhancedNullability P> */.withIndex<@EnhancedNullability P>().first<IndexedValue<@EnhancedNullability P>>()
   val x: Int = <destruct>.component1()
   val y: @EnhancedNullability P = <destruct>.component2() /*!! P */
   use(x = x, y = y)

compiler/testData/ir/irText/types/nullChecks/enhancedNullabilityInForLoop.fir.ir.txt

@@ -7,7 +7,7 @@ FILE fqName:<root> fileName:/enhancedNullabilityInForLoop.kt
       BLOCK type=kotlin.Unit origin=FOR_LOOP
         VAR FOR_LOOP_ITERATOR name:tmp_0 type:kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val]
           CALL 'public abstract fun iterator (): kotlin.collections.MutableIterator<E of kotlin.collections.MutableList> [fake_override,operator] declared in kotlin.collections.MutableList' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=FOR_LOOP_ITERATOR
-            $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? origin=null
+            $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? 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.MutableIterator' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
             $this: GET_VAR 'val tmp_0: kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val] declared in <root>.testForInListUnused' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=null
@@ -22,7 +22,7 @@ FILE fqName:<root> fileName:/enhancedNullabilityInForLoop.kt
       BLOCK type=kotlin.Unit origin=FOR_LOOP
         VAR FOR_LOOP_ITERATOR name:tmp_1 type:kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val]
           CALL 'public abstract fun iterator (): kotlin.collections.MutableIterator<E of kotlin.collections.MutableList> [fake_override,operator] declared in kotlin.collections.MutableList' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=FOR_LOOP_ITERATOR
-            $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? origin=null
+            $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? 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.MutableIterator' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
             $this: GET_VAR 'val tmp_1: kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val] declared in <root>.testForInListDestructured' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=null
@@ -42,7 +42,7 @@ FILE fqName:<root> fileName:/enhancedNullabilityInForLoop.kt
     BLOCK_BODY
       VAR name:iterator type:kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val]
         CALL 'public abstract fun iterator (): kotlin.collections.MutableIterator<E of kotlin.collections.MutableList> [fake_override,operator] declared in kotlin.collections.MutableList' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=null
-          $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? origin=null
+          $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? origin=null
       WHILE label=null origin=WHILE_LOOP
         condition: CALL 'public abstract fun hasNext (): kotlin.Boolean [fake_override,operator] declared in kotlin.collections.MutableIterator' type=kotlin.Boolean origin=null
           $this: GET_VAR 'val iterator: kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val] declared in <root>.testDesugaredForInList' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=null
@@ -73,7 +73,7 @@ FILE fqName:<root> fileName:/enhancedNullabilityInForLoop.kt
       BLOCK type=kotlin.Unit origin=FOR_LOOP
         VAR FOR_LOOP_ITERATOR name:tmp_4 type:kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val]
           CALL 'public abstract fun iterator (): kotlin.collections.MutableIterator<E of kotlin.collections.MutableList> [fake_override,operator] declared in kotlin.collections.MutableList' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=FOR_LOOP_ITERATOR
-            $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? origin=null
+            $this: CALL 'public open fun listOfNotNull (): @[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? declared in <root>.J' type=@[FlexibleNullability] @[FlexibleMutability] kotlin.collections.MutableList<@[EnhancedNullability] <root>.P>? 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.MutableIterator' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
             $this: GET_VAR 'val tmp_4: kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> [val] declared in <root>.testForInListUse' type=kotlin.collections.MutableIterator<@[EnhancedNullability] <root>.P> origin=null

compiler/testData/ir/irText/types/rawTypeInSignature.fir.ir.txt

@@ -84,24 +84,24 @@ FILE fqName:<root> fileName:/rawTypeInSignature.kt
       BLOCK_BODY
         DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:KRaw modality:FINAL visibility:public superTypes:[<root>.JRaw]'
-    FUN DELEGATED_MEMBER name:takesRawList visibility:public modality:OPEN <> ($this:<root>.KRaw, list:@[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>) returnType:kotlin.Unit
+    FUN DELEGATED_MEMBER name:takesRawList visibility:public modality:OPEN <> ($this:<root>.KRaw, list:@[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>) returnType:kotlin.Unit
       overridden:
-        public abstract fun takesRawList (list: @[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>): kotlin.Unit declared in <root>.JRaw
+        public abstract fun takesRawList (list: @[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>): kotlin.Unit declared in <root>.JRaw
       $this: VALUE_PARAMETER name:<this> type:<root>.KRaw
-      VALUE_PARAMETER name:list index:0 type:@[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>
+      VALUE_PARAMETER name:list index:0 type:@[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>
       BLOCK_BODY
-        CALL 'public abstract fun takesRawList (list: @[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>): kotlin.Unit declared in <root>.JRaw' type=kotlin.Unit origin=null
+        CALL 'public abstract fun takesRawList (list: @[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>): kotlin.Unit declared in <root>.JRaw' type=kotlin.Unit origin=null
           $this: GET_FIELD 'FIELD DELEGATE name:$$delegate_0 type:<root>.JRaw visibility:private [final]' type=<root>.JRaw origin=null
             receiver: GET_VAR '<this>: <root>.KRaw declared in <root>.KRaw.takesRawList' type=<root>.KRaw origin=null
-          list: GET_VAR 'list: @[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.KRaw.takesRawList' type=@[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> origin=null
-    FUN DELEGATED_MEMBER name:returnsRawList visibility:public modality:OPEN <> ($this:<root>.KRaw) returnType:@[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>
+          list: GET_VAR 'list: @[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.KRaw.takesRawList' type=@[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> origin=null
+    FUN DELEGATED_MEMBER name:returnsRawList visibility:public modality:OPEN <> ($this:<root>.KRaw) returnType:@[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>
       overridden:
-        public abstract fun returnsRawList (): @[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.JRaw
+        public abstract fun returnsRawList (): @[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.JRaw
       $this: VALUE_PARAMETER name:<this> type:<root>.KRaw
       BLOCK_BODY
-        RETURN type=kotlin.Nothing from='public open fun returnsRawList (): @[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.KRaw'
-          TYPE_OP type=@[RawType] kotlin.collections.MutableList<kotlin.Any?> origin=IMPLICIT_NOTNULL typeOperand=@[RawType] kotlin.collections.MutableList<kotlin.Any?>
-            CALL 'public abstract fun returnsRawList (): @[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.JRaw' type=@[FlexibleNullability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> origin=null
+        RETURN type=kotlin.Nothing from='public open fun returnsRawList (): @[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.KRaw'
+          TYPE_OP type=@[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> origin=IMPLICIT_NOTNULL typeOperand=@[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?>
+            CALL 'public abstract fun returnsRawList (): @[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> declared in <root>.JRaw' type=@[FlexibleNullability] @[FlexibleMutability] @[RawType] kotlin.collections.MutableList<kotlin.Any?> origin=null
               $this: GET_FIELD 'FIELD DELEGATE name:$$delegate_0 type:<root>.JRaw visibility:private [final]' type=<root>.JRaw origin=null
                 receiver: GET_VAR '<this>: <root>.KRaw declared in <root>.KRaw.returnsRawList' type=<root>.KRaw origin=null
     FUN DELEGATED_MEMBER name:takesRawGenericInv visibility:public modality:OPEN <> ($this:<root>.KRaw, g:@[FlexibleNullability] @[RawType] <root>.GenericInv<kotlin.Number>) returnType:kotlin.Unit

compiler/testData/ir/irText/types/rawTypeInSignature.fir.kt.txt

@@ -44,12 +44,12 @@ class KRaw : JRaw {
 
   }
 
-  override fun takesRawList(list: @FlexibleNullability @RawType MutableList<Any?>) {
+  override fun takesRawList(list: @FlexibleNullability @FlexibleMutability @RawType MutableList<Any?>) {
     <this>.#$$delegate_0.takesRawList(list = list)
   }
 
-  override fun returnsRawList(): @FlexibleNullability @RawType MutableList<Any?> {
-    return <this>.#$$delegate_0.returnsRawList() /*!! @RawType MutableList<Any?> */
+  override fun returnsRawList(): @FlexibleNullability @FlexibleMutability @RawType MutableList<Any?> {
+    return <this>.#$$delegate_0.returnsRawList() /*!! @FlexibleMutability @RawType MutableList<Any?> */
   }
 
   override fun takesRawGenericInv(g: @FlexibleNullability @RawType GenericInv<Number>) {
@@ -79,3 +79,4 @@ class KRaw : JRaw {
   private /* final field */ val $$delegate_0: JRaw = j
 
 }
+

core/compiler.common/src/org/jetbrains/kotlin/name/StandardClassIds.kt

@@ -174,6 +174,7 @@ object StandardClassIds {
 
         val RawTypeAnnotation = "RawType".internalIrId()
         val FlexibleNullability = "FlexibleNullability".internalIrId()
+        val FlexibleMutability = "FlexibleMutability".internalIrId()
         val EnhancedNullability = "EnhancedNullability".jvmInternalId()
 
         val InlineOnly = "InlineOnly".internalId()

core/compiler.common/src/org/jetbrains/kotlin/types/CommonFlexibleTypeBoundsChecker.kt

@@ -0,0 +1,27 @@
+/*
+ * 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.types
+
+import org.jetbrains.kotlin.builtins.StandardNames.FqNames
+import org.jetbrains.kotlin.name.FqName
+
+object CommonFlexibleTypeBoundsChecker {
+    val baseTypesToMutableEquivalent = mapOf(
+        FqNames.iterable to FqNames.mutableIterable,
+        FqNames.iterator to FqNames.mutableIterator,
+        FqNames.listIterator to FqNames.mutableListIterator,
+        FqNames.list to FqNames.mutableList,
+        FqNames.collection to FqNames.mutableCollection,
+        FqNames.set to FqNames.mutableSet,
+        FqNames.map to FqNames.mutableMap,
+        FqNames.mapEntry to FqNames.mutableMapEntry
+    )
+    val mutableToBaseMap = baseTypesToMutableEquivalent.entries.associateBy({ it.value }) { it.key }
+
+    fun getBaseBoundFqNameByMutability(fqName: FqName): FqName? =
+        if (fqName in baseTypesToMutableEquivalent) fqName
+        else mutableToBaseMap[fqName]
+}

core/descriptors/src/org/jetbrains/kotlin/types/flexibleTypes.kt

@@ -154,22 +154,11 @@ class FlexibleTypeImpl(lowerBound: SimpleType, upperBound: SimpleType) : Flexibl
 }
 
 object FlexibleTypeBoundsChecker {
-    private val fqNames = StandardNames.FqNames
-    private val baseTypesToMutableEquivalent = mapOf(
-        fqNames.iterable to fqNames.mutableIterable,
-        fqNames.iterator to fqNames.mutableIterator,
-        fqNames.listIterator to fqNames.mutableListIterator,
-        fqNames.list to fqNames.mutableList,
-        fqNames.collection to fqNames.mutableCollection,
-        fqNames.set to fqNames.mutableSet,
-        fqNames.map to fqNames.mutableMap,
-        fqNames.mapEntry to fqNames.mutableMapEntry
-    )
-    private val mutableToBaseMap = baseTypesToMutableEquivalent.entries.associateBy({ it.value }) { it.key }
-
     fun areTypesMayBeLowerAndUpperBoundsOfSameFlexibleTypeByMutability(a: KotlinType, b: KotlinType): Boolean {
         val fqName = a.constructor.declarationDescriptor?.fqNameSafe ?: return false
-        val possiblePairBound = (baseTypesToMutableEquivalent[fqName] ?: mutableToBaseMap[fqName]) ?: return false
+        val possiblePairBound = (CommonFlexibleTypeBoundsChecker.baseTypesToMutableEquivalent[fqName]
+            ?: CommonFlexibleTypeBoundsChecker.mutableToBaseMap[fqName])
+            ?: return false
 
         return possiblePairBound == b.constructor.declarationDescriptor?.fqNameSafe
     }
@@ -178,7 +167,7 @@ object FlexibleTypeBoundsChecker {
     fun getBaseBoundFqNameByMutability(type: KotlinType): FqName? =
         type.constructor.declarationDescriptor?.fqNameSafe?.let(::getBaseBoundFqNameByMutability)
 
-    fun getBaseBoundFqNameByMutability(fqName: FqName): FqName? =
-        if (fqName in baseTypesToMutableEquivalent) fqName
-        else mutableToBaseMap[fqName]
+    fun getBaseBoundFqNameByMutability(fqName: FqName): FqName? {
+        return CommonFlexibleTypeBoundsChecker.getBaseBoundFqNameByMutability(fqName)
+    }
 }