Support mutable collection types in typeOf

flexibleTypes_1_6.kt is fixed for JVM IR in a subsequent commit.

 #KT-35877 Fixed

libraries/stdlib/jvm/runtime/kotlin/jvm/internal/Reflection.java

@@ -190,4 +190,9 @@ public class Reflection {
     public static KType platformType(KType lowerBound, KType upperBound) {
         return factory.platformType(lowerBound, upperBound);
     }
+
+    @SinceKotlin(version = "1.6")
+    public static KType mutableCollectionType(KType type) {
+        return factory.mutableCollectionType(type);
+    }
 }

libraries/stdlib/jvm/runtime/kotlin/jvm/internal/ReflectionFactory.java

@@ -96,6 +96,19 @@ public class ReflectionFactory {
 
     @SinceKotlin(version = "1.6")
     public KType platformType(KType lowerBound, KType upperBound) {
-        return new TypeReference(lowerBound.getClassifier(), lowerBound.getArguments(), lowerBound.isMarkedNullable(), upperBound);
+        return new TypeReference(
+                lowerBound.getClassifier(), lowerBound.getArguments(), lowerBound.isMarkedNullable(),
+                upperBound,
+                ((TypeReference) lowerBound).getMutableCollectionType$kotlin_stdlib()
+        );
+    }
+
+    @SinceKotlin(version = "1.6")
+    public KType mutableCollectionType(KType type) {
+        return new TypeReference(
+                type.getClassifier(), type.getArguments(), type.isMarkedNullable(),
+                ((TypeReference) type).getPlatformTypeUpperBound$kotlin_stdlib(),
+                true
+        );
     }
 }

libraries/stdlib/jvm/runtime/kotlin/jvm/internal/TypeReference.kt

@@ -14,13 +14,14 @@ public class TypeReference /* @SinceKotlin("1.6") constructor */(
     override val classifier: KClassifier,
     override val arguments: List<KTypeProjection>,
     override val isMarkedNullable: Boolean,
-    private val platformTypeUpperBound: KType?,
+    internal val platformTypeUpperBound: KType?,
+    internal val mutableCollectionType: Boolean,
 ) : KType {
     constructor(
         classifier: KClassifier,
         arguments: List<KTypeProjection>,
         isMarkedNullable: Boolean,
-    ) : this(classifier, arguments, isMarkedNullable, null)
+    ) : this(classifier, arguments, isMarkedNullable, null, false)
 
     override val annotations: List<Annotation>
         get() = emptyList()
@@ -28,7 +29,7 @@ public class TypeReference /* @SinceKotlin("1.6") constructor */(
     override fun equals(other: Any?): Boolean =
         other is TypeReference &&
                 classifier == other.classifier && arguments == other.arguments && isMarkedNullable == other.isMarkedNullable &&
-                platformTypeUpperBound == other.platformTypeUpperBound
+                platformTypeUpperBound == other.platformTypeUpperBound && mutableCollectionType == other.mutableCollectionType
 
     override fun hashCode(): Int =
         (classifier.hashCode() * 31 + arguments.hashCode()) * 31 + isMarkedNullable.hashCode()