diff --git a/compiler/testData/diagnostics/tests/j+k/InheritedGenericFunction.txt b/compiler/testData/diagnostics/tests/j+k/InheritedGenericFunction.txt
index 957c80652dd..51db85258e4 100644
--- a/compiler/testData/diagnostics/tests/j+k/InheritedGenericFunction.txt
+++ b/compiler/testData/diagnostics/tests/j+k/InheritedGenericFunction.txt
@@ -3,7 +3,7 @@ package
 public abstract class K : p.C {
     public constructor K()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun </*0*/ TB : kotlin.Any!> foo(/*0*/ p: TB!): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun </*0*/ TA : kotlin.Any!> foo(/*0*/ p: TA!): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableList.txt b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableList.txt
index 82a7679aa40..675f33252ac 100644
--- a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableList.txt
+++ b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableList.txt
@@ -6,25 +6,25 @@ public open class A : AImpl, kotlin.MutableList<kotlin.String!> {
     public constructor A()
     public open override /*2*/ /*fake_override*/ val size: kotlin.Int
     public open override /*2*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun add(/*0*/ element: kotlin.String!): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun add(/*0*/ s: kotlin.String!): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun clear(): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun contains(/*0*/ o: kotlin.String!): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.String!): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String!
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ o: kotlin.String!): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String!): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.String!>
-    public open override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ o: kotlin.String!): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.String!): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.String!>
     public open override /*2*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.String!>
-    public open override /*2*/ /*fake_override*/ fun remove(/*0*/ o: kotlin.String!): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun removeAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun remove(/*0*/ element: kotlin.String!): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.String!
-    public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.String!
     public open override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String!>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
@@ -66,25 +66,25 @@ public final class X : A {
     public constructor X()
     public open override /*1*/ /*fake_override*/ val size: kotlin.Int
     public open override /*1*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.Unit
-    public open override /*1*/ /*fake_override*/ fun add(/*0*/ element: kotlin.String!): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun add(/*0*/ s: kotlin.String!): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun clear(): kotlin.Unit
-    public open override /*1*/ /*fake_override*/ fun contains(/*0*/ o: kotlin.String!): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun containsAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.String!): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String!
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun indexOf(/*0*/ o: kotlin.String!): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String!): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.String!>
-    public open override /*1*/ /*fake_override*/ fun lastIndexOf(/*0*/ o: kotlin.String!): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.String!): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.String!>
     public open override /*1*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.String!>
-    public open override /*1*/ /*fake_override*/ fun remove(/*0*/ o: kotlin.String!): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun removeAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun remove(/*0*/ element: kotlin.String!): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.String!
-    public open override /*1*/ /*fake_override*/ fun retainAll(/*0*/ c: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.String!
     public open override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String!>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
diff --git a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableListKotlin.txt b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableListKotlin.txt
index 154d693a1cc..7d4011e854b 100644
--- a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableListKotlin.txt
+++ b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableListKotlin.txt
@@ -5,28 +5,28 @@ public fun main(): kotlin.Unit
 public open class A : AImpl, kotlin.MutableList<kotlin.String!> {
     public constructor A()
     public final override /*2*/ /*fake_override*/ val size: kotlin.Int
-    public final override /*2*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.Unit
-    public final override /*2*/ /*fake_override*/ fun add(/*0*/ element: kotlin.String!): kotlin.Boolean
-    public final override /*2*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
-    public final override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public final override /*2*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String): kotlin.Unit
+    public final override /*2*/ /*fake_override*/ fun add(/*0*/ element: kotlin.String): kotlin.Boolean
+    public final override /*2*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
+    public final override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
     public final override /*2*/ /*fake_override*/ fun clear(): kotlin.Unit
     public final override /*2*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.String!): kotlin.Boolean
     public final override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public final override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public final override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String!): kotlin.Int
+    public final override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String): kotlin.Int
     public final override /*2*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
-    public final override /*2*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.String!>
-    public final override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.String!): kotlin.Int
-    public final override /*2*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.String!>
-    public final override /*2*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.String!>
-    public final override /*2*/ /*fake_override*/ fun remove(/*0*/ element: kotlin.String!): kotlin.Boolean
-    public final override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public final override /*2*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.String>
+    public final override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.String): kotlin.Int
+    public final override /*2*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.String>
+    public final override /*2*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.String>
+    public final override /*2*/ /*fake_override*/ fun remove(/*0*/ element: kotlin.String): kotlin.Boolean
+    public final override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
     public final override /*2*/ /*fake_override*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.String
-    public final override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public final override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
     public final override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String): kotlin.String
-    public final override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String!>
+    public final override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String>
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
@@ -61,27 +61,27 @@ public abstract class AImpl {
 public final class X : A {
     public constructor X()
     public final override /*1*/ /*fake_override*/ val size: kotlin.Int
-    public final override /*1*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.Unit
-    public final override /*1*/ /*fake_override*/ fun add(/*0*/ element: kotlin.String!): kotlin.Boolean
-    public final override /*1*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
-    public final override /*1*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ fun add(/*0*/ element: kotlin.String): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun clear(): kotlin.Unit
     public final override /*1*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.String!): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public final override /*1*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String!): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String): kotlin.Int
     public final override /*1*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
-    public final override /*1*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.String!>
-    public final override /*1*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.String!): kotlin.Int
-    public final override /*1*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.String!>
-    public final override /*1*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.String!>
-    public final override /*1*/ /*fake_override*/ fun remove(/*0*/ element: kotlin.String!): kotlin.Boolean
-    public final override /*1*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.String>
+    public final override /*1*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.String): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.String>
+    public final override /*1*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.String>
+    public final override /*1*/ /*fake_override*/ fun remove(/*0*/ element: kotlin.String): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.String
-    public final override /*1*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String>): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String): kotlin.String
-    public final override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String!>
+    public final override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String>
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAt.txt b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAt.txt
index 660bb1265c6..84b1899485e 100644
--- a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAt.txt
+++ b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAt.txt
@@ -45,31 +45,31 @@ public abstract class B</*0*/ T> : kotlin.MutableList<T>, java.util.AbstractList
     public constructor B</*0*/ T>()
     protected/*protected and package*/ final override /*1*/ /*fake_override*/ var modCount: kotlin.Int
     public abstract override /*2*/ /*fake_override*/ val size: kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun add(/*0*/ element: T!): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: T!): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<T!>): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<T!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun add(/*0*/ element: T): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: T): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<T>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<T>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun clear(): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun contains(/*0*/ element: T!): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<T!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun contains(/*0*/ element: T): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<T>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public abstract override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): T
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: T!): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: T): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<T!>
-    public open override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: T!): kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<T!>
-    public open override /*2*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<T!>
+    public open override /*2*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<T>
+    public open override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: T): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<T>
+    public open override /*2*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<T>
     invisible_fake open override /*1*/ /*fake_override*/ fun outOfBoundsMsg(/*0*/ p0: kotlin.Int): kotlin.String!
     invisible_fake open override /*1*/ /*fake_override*/ fun rangeCheckForAdd(/*0*/ p0: kotlin.Int): kotlin.Unit
     public open override /*2*/ fun remove(/*0*/ element: T): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<T!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<T>): kotlin.Boolean
     public open override /*2*/ fun removeAt(/*0*/ index: kotlin.Int): T
     protected/*protected and package*/ open override /*1*/ /*fake_override*/ fun removeRange(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<T!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<T>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: T): T
-    public open override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<T!>
+    public open override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<T>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
     public open override /*1*/ /*fake_override*/ fun </*0*/ T : kotlin.Any!> toArray(/*0*/ p0: kotlin.Array<(out) T!>!): kotlin.Array<(out) T!>!
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
diff --git a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAtInt.txt b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAtInt.txt
index aaaf61eb9d7..708b185a4e1 100644
--- a/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAtInt.txt
+++ b/compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAtInt.txt
@@ -6,31 +6,31 @@ public abstract class A : B {
     public constructor A()
     protected/*protected and package*/ final override /*1*/ /*fake_override*/ var modCount: kotlin.Int
     public abstract override /*1*/ /*fake_override*/ val size: kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int!): kotlin.Unit
-    public open override /*1*/ /*fake_override*/ fun add(/*0*/ element: kotlin.Int!): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun add(/*0*/ element: kotlin.Int): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun clear(): kotlin.Unit
-    public open override /*1*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.Int!): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.Int): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public abstract override /*1*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.Int!): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.Int): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.Int!>
-    public open override /*1*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.Int!): kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.Int!>
-    public open override /*1*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.Int!>
+    public open override /*1*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.Int>
+    public open override /*1*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.Int): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.Int>
+    public open override /*1*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.Int>
     invisible_fake open override /*1*/ /*fake_override*/ fun outOfBoundsMsg(/*0*/ p0: kotlin.Int): kotlin.String!
     invisible_fake open override /*1*/ /*fake_override*/ fun rangeCheckForAdd(/*0*/ p0: kotlin.Int): kotlin.Unit
     public open override /*1*/ fun remove(/*0*/ element: kotlin.Int): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*1*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.Int
     protected/*protected and package*/ open override /*1*/ /*fake_override*/ fun removeRange(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int): kotlin.Unit
-    public open override /*1*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int): kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.Int!>
+    public open override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.Int>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
     public open override /*1*/ /*fake_override*/ fun </*0*/ T : kotlin.Any!> toArray(/*0*/ p0: kotlin.Array<(out) T!>!): kotlin.Array<(out) T!>!
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
@@ -45,31 +45,31 @@ public abstract class B : kotlin.MutableList<kotlin.Int>, java.util.AbstractList
     public constructor B()
     protected/*protected and package*/ final override /*1*/ /*fake_override*/ var modCount: kotlin.Int
     public abstract override /*2*/ /*fake_override*/ val size: kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int!): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun add(/*0*/ element: kotlin.Int!): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun add(/*0*/ element: kotlin.Int): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun add(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun addAll(/*0*/ index: kotlin.Int, /*1*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun clear(): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.Int!): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.Int): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public abstract override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.Int!): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.Int): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.Int!>
-    public open override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.Int!): kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.Int!>
-    public open override /*2*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.Int!>
+    public open override /*2*/ /*fake_override*/ fun iterator(): kotlin.MutableIterator<kotlin.Int>
+    public open override /*2*/ /*fake_override*/ fun lastIndexOf(/*0*/ element: kotlin.Int): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun listIterator(): kotlin.MutableListIterator<kotlin.Int>
+    public open override /*2*/ /*fake_override*/ fun listIterator(/*0*/ index: kotlin.Int): kotlin.MutableListIterator<kotlin.Int>
     invisible_fake open override /*1*/ /*fake_override*/ fun outOfBoundsMsg(/*0*/ p0: kotlin.Int): kotlin.String!
     invisible_fake open override /*1*/ /*fake_override*/ fun rangeCheckForAdd(/*0*/ p0: kotlin.Int): kotlin.Unit
     public open override /*2*/ fun remove(/*0*/ element: kotlin.Int): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*2*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.Int
     protected/*protected and package*/ open override /*1*/ /*fake_override*/ fun removeRange(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int): kotlin.Unit
-    public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.Int>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int): kotlin.Int
-    public open override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.Int!>
+    public open override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.Int>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
     public open override /*1*/ /*fake_override*/ fun </*0*/ T : kotlin.Any!> toArray(/*0*/ p0: kotlin.Array<(out) T!>!): kotlin.Array<(out) T!>!
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
diff --git a/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt b/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt
index c28413e261b..840cd67c417 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt
+++ b/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt
@@ -11,7 +11,7 @@ public open class J</*0*/ T : kotlin.Any!> : ML<T!> {
 public final class K : J<kotlin.String>, ML<kotlin.String> {
     public constructor K()
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String!>
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments1.txt b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments1.txt
index 8a41feb7b32..3f856820e78 100644
--- a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments1.txt
+++ b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments1.txt
@@ -19,7 +19,7 @@ public interface B {
 
 public interface C : A, B {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ y: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ x: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -27,14 +27,14 @@ public interface C : A, B {
 public abstract class C1 : A, B {
     public constructor C1()
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ y: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ x: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 public interface D : B, A {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ x: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ y: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -42,7 +42,7 @@ public interface D : B, A {
 public abstract class D1 : A, B {
     public constructor D1()
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ y: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ x: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments2.txt b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments2.txt
index f57cafc31c9..f490eb78fe3 100644
--- a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments2.txt
+++ b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArguments2.txt
@@ -21,10 +21,10 @@ public interface B {
 }
 
 public interface C : A, B {
-    public abstract override /*2*/ /*fake_override*/ fun bar(/*0*/ a1: kotlin.Int, /*1*/ a2: kotlin.Double, /*2*/ b3: kotlin.String): kotlin.Unit
-    public abstract override /*2*/ /*fake_override*/ fun baz(/*0*/ a1: kotlin.Int, /*1*/ b2: kotlin.Double, /*2*/ a3: kotlin.String, /*3*/ b4: kotlin.Int, /*4*/ a5: kotlin.String): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun bar(/*0*/ a1: kotlin.Int, /*1*/ a2: kotlin.Double, /*2*/ a3: kotlin.String): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun baz(/*0*/ a1: kotlin.Int, /*1*/ a2: kotlin.Double, /*2*/ a3: kotlin.String, /*3*/ a4: kotlin.Int, /*4*/ a5: kotlin.String): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ b1: kotlin.Int, /*1*/ b2: kotlin.Double): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ a1: kotlin.Int, /*1*/ a2: kotlin.Double): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics1.txt b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics1.txt
index 55fa905c78c..68c6da0631d 100644
--- a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics1.txt
+++ b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics1.txt
@@ -18,7 +18,7 @@ public interface B {
 
 public interface C : A<kotlin.Int>, B {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ b: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ a: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics2.txt b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics2.txt
index f8c8e143a20..f7823de6f1f 100644
--- a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics2.txt
+++ b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics2.txt
@@ -18,7 +18,7 @@ public interface B {
 
 public interface C : A, B {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun </*0*/ T> foo(/*0*/ b: T): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun </*0*/ E> foo(/*0*/ a: E): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics3.txt b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics3.txt
index f89aa6b9b6b..914b214f679 100644
--- a/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics3.txt
+++ b/compiler/testData/diagnostics/tests/namedArguments/ambiguousNamedArgumentsWithGenerics3.txt
@@ -18,7 +18,7 @@ public interface B</*0*/ E> {
 
 public interface C</*0*/ U> : A<U>, B<U> {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ b: U): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ a: U): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/namedArguments/namedArgumentsInOverrides.txt b/compiler/testData/diagnostics/tests/namedArguments/namedArgumentsInOverrides.txt
index c588127cc5a..560e2366300 100644
--- a/compiler/testData/diagnostics/tests/namedArguments/namedArgumentsInOverrides.txt
+++ b/compiler/testData/diagnostics/tests/namedArguments/namedArgumentsInOverrides.txt
@@ -19,7 +19,7 @@ public interface B {
 
 public interface C : A, B {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ b1: kotlin.Int, /*1*/ b2: kotlin.Double): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ a1: kotlin.Int, /*1*/ a2: kotlin.Double): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt
index e8d2abf8119..fae82e55ad3 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.kt
@@ -11,4 +11,4 @@ interface C {
 }
 
 // TODO DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES reported twice
-<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE, DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES, DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES!>class Z<!> : A, B(), C
\ No newline at end of file
+<!MULTIPLE_DEFAULTS_INHERITED_FROM_SUPERTYPES_WHEN_NO_EXPLICIT_OVERRIDE, DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES!>class Z<!> : A, B(), C
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.txt b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.txt
index 335c53c5393..aa567876a11 100644
--- a/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.txt
+++ b/compiler/testData/diagnostics/tests/override/MultipleDefaultsAndNamesInSupertypes.txt
@@ -25,7 +25,7 @@ public interface C {
 public final class Z : A, B, C {
     public constructor Z()
     public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public final override /*3*/ /*fake_override*/ fun foo(/*0*/ y: kotlin.Int = ...): kotlin.Int
+    public final override /*3*/ /*fake_override*/ fun foo(/*0*/ x: kotlin.Int = ...): kotlin.Int
     public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeIn.txt b/compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeIn.txt
index 742c794aadb..8e8e7d9af33 100644
--- a/compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeIn.txt
+++ b/compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeIn.txt
@@ -68,21 +68,21 @@ public interface TestJ1K2 : J1, K2 {
 
 public interface TestJ2K1 : J2, K1 {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String>
+    @org.jetbrains.annotations.NotNull() public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String!>
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 public interface TestJ2K1K2 : J2, K1, K2 {
     public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    @org.jetbrains.annotations.NotNull() public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String!>
     public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 public interface TestJ2K2 : J2, K2 {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    @org.jetbrains.annotations.NotNull() public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String!>
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -124,14 +124,14 @@ public interface TestK1J1K2 : K1, J1, K2 {
 
 public interface TestK1J2 : K1, J2 {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    @org.jetbrains.annotations.NotNull() public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String!>
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String>
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 public interface TestK1J2K2 : K1, J2, K2 {
     public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    @org.jetbrains.annotations.NotNull() public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String!>
     public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -159,7 +159,7 @@ public interface TestK1K2J1 : K1, K2, J1 {
 
 public interface TestK1K2J2 : K1, K2, J2 {
     public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    @org.jetbrains.annotations.NotNull() public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String!>
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
     public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -180,7 +180,7 @@ public interface TestK2J1 : K2, J1 {
 
 public interface TestK2J2 : K2, J2 {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    @org.jetbrains.annotations.NotNull() public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String!>
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String?>
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.txt b/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.txt
index 28702836728..923f716eaad 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.txt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/differentNamesInSupertypesDiagnostic.txt
@@ -16,7 +16,7 @@ public interface D {
 
 public interface E : C, D {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ b: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ a: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.txt b/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.txt
index e9d04cf9856..66c283c9e30 100644
--- a/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.txt
+++ b/compiler/testData/diagnostics/tests/override/parameterNames/kotlinInheritsBothJavaAndKotlin.txt
@@ -5,7 +5,7 @@ public/*package*/ /*synthesized*/ fun JavaInterface(/*0*/ function: (kotlin.Int)
 public final class BothTraitsSubclass : JavaInterface, KotlinTrait {
     public constructor BothTraitsSubclass()
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun foo(/*0*/ someOtherName: kotlin.Int): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun foo(/*0*/ javaName: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
diff --git a/compiler/testData/diagnostics/tests/platformTypes/rawOverrides.txt b/compiler/testData/diagnostics/tests/platformTypes/rawOverrides.txt
index c22d37263b4..1d4414ebae3 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/rawOverrides.txt
+++ b/compiler/testData/diagnostics/tests/platformTypes/rawOverrides.txt
@@ -33,10 +33,10 @@ public open class D : C {
 public final class E : D, B {
     public constructor E()
     public open override /*1*/ fun bar(/*0*/ x: kotlin.CharSequence?, /*1*/ y: kotlin.List<*>?): kotlin.String
-    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any(raw)?): kotlin.Boolean(raw)
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ fun foo(/*0*/ x: kotlin.Any, /*1*/ y: kotlin.List<kotlin.Any?>): kotlin.String
-    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int(raw)
-    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String(raw)
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 public final class E2 : B {
diff --git a/compiler/testData/diagnostics/tests/regressions/kt1639-JFrame.txt b/compiler/testData/diagnostics/tests/regressions/kt1639-JFrame.txt
index 4ee57f809a1..4b9afe3e70d 100644
--- a/compiler/testData/diagnostics/tests/regressions/kt1639-JFrame.txt
+++ b/compiler/testData/diagnostics/tests/regressions/kt1639-JFrame.txt
@@ -558,12 +558,12 @@ package test {
         invisible_fake open override /*1*/ /*fake_override*/ fun reparentChild(/*0*/ p0: java.awt.Component!): kotlin.Unit
         invisible_fake open override /*1*/ /*fake_override*/ fun reparentTraverse(/*0*/ p0: [ERROR : Unresolved java classifier: ContainerPeer]!, /*1*/ p1: java.awt.Container!): kotlin.Unit
         public open override /*1*/ /*fake_override*/ fun requestFocus(): kotlin.Unit
-        public open override /*1*/ /*fake_override*/ fun requestFocus(/*0*/ p0: [ERROR : Unresolved java classifier: Cause]!): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun requestFocus(/*0*/ p0: kotlin.Boolean): kotlin.Boolean
         invisible_fake open override /*1*/ /*fake_override*/ fun requestFocus(/*0*/ p0: kotlin.Boolean, /*1*/ p1: [ERROR : Unresolved java classifier: Cause]!): kotlin.Boolean
         invisible_fake final override /*1*/ /*fake_override*/ fun requestFocusHelper(/*0*/ p0: kotlin.Boolean, /*1*/ p1: kotlin.Boolean): kotlin.Boolean
         invisible_fake final override /*1*/ /*fake_override*/ fun requestFocusHelper(/*0*/ p0: kotlin.Boolean, /*1*/ p1: kotlin.Boolean, /*2*/ p2: [ERROR : Unresolved java classifier: Cause]!): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun requestFocusInWindow(): kotlin.Boolean
-        public open override /*1*/ /*fake_override*/ fun requestFocusInWindow(/*0*/ p0: [ERROR : Unresolved java classifier: Cause]!): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun requestFocusInWindow(/*0*/ p0: kotlin.Boolean): kotlin.Boolean
         invisible_fake open override /*1*/ /*fake_override*/ fun requestFocusInWindow(/*0*/ p0: kotlin.Boolean, /*1*/ p1: [ERROR : Unresolved java classifier: Cause]!): kotlin.Boolean
         @kotlin.Deprecated(message = "Deprecated in Java") public open override /*1*/ /*fake_override*/ fun reshape(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int, /*2*/ p2: kotlin.Int, /*3*/ p3: kotlin.Int): kotlin.Unit
         invisible_fake open override /*1*/ /*fake_override*/ fun reshapeNativePeer(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int, /*2*/ p2: kotlin.Int, /*3*/ p3: kotlin.Int, /*4*/ p4: kotlin.Int): kotlin.Unit
diff --git a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.txt b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.txt
index ec27421001e..02113b84915 100644
--- a/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.txt
+++ b/compiler/testData/loadJava/kotlinAgainstCompiledJavaWithKotlin/InheritParameterName.txt
@@ -12,10 +12,10 @@ public interface B {
 
 public abstract class ZAB : test.A, test.B {
     public constructor ZAB()
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ kotlinName: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ p0: kotlin.Int): kotlin.Unit
 }
 
 public abstract class ZBA : test.B, test.A {
     public constructor ZBA()
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ p0: kotlin.Int): kotlin.Unit
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ kotlinName: kotlin.Int): kotlin.Unit
 }
diff --git a/core/descriptors/src/org/jetbrains/kotlin/resolve/OverridingUtil.java b/core/descriptors/src/org/jetbrains/kotlin/resolve/OverridingUtil.java
index 532d50a1894..81c8f744ed6 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/resolve/OverridingUtil.java
+++ b/core/descriptors/src/org/jetbrains/kotlin/resolve/OverridingUtil.java
@@ -395,17 +395,18 @@ public class OverridingUtil {
             return CollectionsKt.first(candidates);
         }
 
-        CallableMemberDescriptor lastNonFlexible = null;
+        CallableMemberDescriptor firstNonFlexible = null;
         for (CallableMemberDescriptor candidate : candidates) {
-            if (!FlexibleTypesKt.isFlexible(candidate.getReturnType())) {
-                lastNonFlexible = candidate;
+            if (firstNonFlexible == null && !FlexibleTypesKt.isFlexible(candidate.getReturnType())) {
+                firstNonFlexible = candidate;
+                break;
             }
         }
-        if (lastNonFlexible != null) {
-            return lastNonFlexible;
+        if (firstNonFlexible != null) {
+            return firstNonFlexible;
         }
 
-        return CollectionsKt.last(candidates);
+        return CollectionsKt.first(candidates);
     }
 
     private static void createAndBindFakeOverride(