Have mutable collection interfaces specified explicitly to get rid of platform types in parameter and return types.

libraries/stdlib/src/kotlin/collections/AbstractMutableCollection.kt

@@ -4,6 +4,6 @@ package kotlin.collections
 import java.util.AbstractCollection
 
 @SinceKotlin("1.1")
-public abstract class AbstractMutableCollection<E> protected constructor() : AbstractCollection<E>() {
+public abstract class AbstractMutableCollection<E> protected constructor() : MutableCollection<E>, AbstractCollection<E>() {
     abstract override fun add(element: E): Boolean
 }

libraries/stdlib/src/kotlin/collections/AbstractMutableList.kt

@@ -4,7 +4,7 @@ package kotlin.collections
 import java.util.AbstractList
 
 @SinceKotlin("1.1")
-public abstract class AbstractMutableList<E> protected constructor() : AbstractList<E>() {
+public abstract class AbstractMutableList<E> protected constructor() : MutableList<E>, AbstractList<E>() {
     abstract override fun set(index: Int, element: E): E
     abstract override fun removeAt(index: Int): E
     abstract override fun add(index: Int, element: E)

libraries/stdlib/src/kotlin/collections/AbstractMutableMap.kt

@@ -4,6 +4,6 @@ package kotlin.collections
 import java.util.AbstractMap
 
 @SinceKotlin("1.1")
-public abstract class AbstractMutableMap<K, V> protected constructor() : AbstractMap<K, V>() {
+public abstract class AbstractMutableMap<K, V> protected constructor() : MutableMap<K, V>, AbstractMap<K, V>() {
     abstract override fun put(key: K, value: V): V?
 }

libraries/stdlib/src/kotlin/collections/AbstractMutableSet.kt

@@ -4,6 +4,7 @@ package kotlin.collections
 import java.util.AbstractSet
 
 @SinceKotlin("1.1")
-public abstract class AbstractMutableSet<E> protected constructor() : AbstractSet<E>() {
-    // nothing to make abstract, maybe leave it typealias then?
+public abstract class AbstractMutableSet<E> protected constructor() : MutableSet<E>, AbstractSet<E>() {
+    // nothing to make abstract
+    // it's a class rather than typealias in order to have bridge for `size` generated and nice non-platform types in methods
 }

libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-stdlib.txt

@@ -138,14 +138,14 @@ public abstract class kotlin/collections/AbstractMap : java/util/Map, kotlin/jvm
 	public final fun values ()Ljava/util/Collection;
 }
 
-public abstract class kotlin/collections/AbstractMutableCollection : java/util/AbstractCollection {
+public abstract class kotlin/collections/AbstractMutableCollection : java/util/AbstractCollection, java/util/Collection, kotlin/jvm/internal/markers/KMutableCollection {
 	protected fun <init> ()V
 	public abstract fun add (Ljava/lang/Object;)Z
 	public abstract fun getSize ()I
 	public final fun size ()I
 }
 
-public abstract class kotlin/collections/AbstractMutableList : java/util/AbstractList {
+public abstract class kotlin/collections/AbstractMutableList : java/util/AbstractList, java/util/List, kotlin/jvm/internal/markers/KMutableList {
 	protected fun <init> ()V
 	public abstract fun add (ILjava/lang/Object;)V
 	public abstract fun getSize ()I
@@ -155,7 +155,7 @@ public abstract class kotlin/collections/AbstractMutableList : java/util/Abstrac
 	public final fun size ()I
 }
 
-public abstract class kotlin/collections/AbstractMutableMap : java/util/AbstractMap {
+public abstract class kotlin/collections/AbstractMutableMap : java/util/AbstractMap, java/util/Map, kotlin/jvm/internal/markers/KMutableMap {
 	protected fun <init> ()V
 	public final fun entrySet ()Ljava/util/Set;
 	public abstract fun getEntries ()Ljava/util/Set;
@@ -168,7 +168,7 @@ public abstract class kotlin/collections/AbstractMutableMap : java/util/Abstract
 	public final fun values ()Ljava/util/Collection;
 }
 
-public abstract class kotlin/collections/AbstractMutableSet : java/util/AbstractSet {
+public abstract class kotlin/collections/AbstractMutableSet : java/util/AbstractSet, java/util/Set, kotlin/jvm/internal/markers/KMutableSet {
 	protected fun <init> ()V
 	public abstract fun getSize ()I
 	public final fun size ()I