Do subtyping with stub types properly

1) Return stub type if we are calculating super type between two same stub types
2) Return nullable Any if those stub types are different

core/descriptors/src/org/jetbrains/kotlin/renderer/DescriptorRendererImpl.kt

@@ -288,7 +288,11 @@ internal class DescriptorRendererImpl(
 
     override fun renderTypeConstructor(typeConstructor: TypeConstructor): String = when (val cd = typeConstructor.declarationDescriptor) {
         is TypeParameterDescriptor, is ClassDescriptor, is TypeAliasDescriptor -> renderClassifierName(cd)
-        null -> typeConstructor.toString()
+        null -> {
+            if (typeConstructor is IntersectionTypeConstructor) {
+                typeConstructor.makeDebugNameForIntersectionType { if (it is StubType) it.originalTypeVariable else it }
+            } else typeConstructor.toString()
+        }
         else -> error("Unexpected classifier: " + cd::class.java)
     }
 

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

@@ -61,11 +61,12 @@ class IntersectionTypeConstructor(typesToIntersect: Collection<KotlinType>) : Ty
     override fun getBuiltIns(): KotlinBuiltIns =
         intersectedTypes.iterator().next().constructor.builtIns
 
-    override fun toString(): String =
-        makeDebugNameForIntersectionType(intersectedTypes)
+    override fun toString(): String = makeDebugNameForIntersectionType()
 
-    private fun makeDebugNameForIntersectionType(resultingTypes: Iterable<KotlinType>): String =
-        resultingTypes.sortedBy { it.toString() }.joinToString(separator = " & ", prefix = "{", postfix = "}")
+    fun makeDebugNameForIntersectionType(getProperTypeRelatedToStringify: (KotlinType) -> Any = { it.toString() }): String {
+        return intersectedTypes.sortedBy { getProperTypeRelatedToStringify(it).toString() }
+            .joinToString(separator = " & ", prefix = "{", postfix = "}") { getProperTypeRelatedToStringify(it).toString() }
+    }
 
     override fun equals(other: Any?): Boolean {
         if (this === other) return true

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

@@ -23,6 +23,17 @@ class StubType(
     }
 }
 
+class StubTypeForTypeVariablesInSubtyping(
+    originalTypeVariable: TypeConstructor,
+    isMarkedNullable: Boolean,
+    constructor: TypeConstructor = ErrorUtils.createErrorTypeConstructor("Constructor for non fixed type: $originalTypeVariable"),
+    memberScope: MemberScope = ErrorUtils.createErrorScope("Scope for non fixed type: $originalTypeVariable")
+) : AbstractStubType(originalTypeVariable, isMarkedNullable, constructor, memberScope), StubTypeMarker {
+    override fun materialize(newNullability: Boolean): AbstractStubType {
+        return StubTypeForTypeVariablesInSubtyping(originalTypeVariable, newNullability, constructor, memberScope)
+    }
+}
+
 // This type is used as a replacement of type variables for provideDelegate resolve
 class StubTypeForProvideDelegateReceiver(
     originalTypeVariable: TypeConstructor,
@@ -54,7 +65,7 @@ abstract class AbstractStubType(
     }
 
     override fun toString(): String {
-        return "NonFixed: $originalTypeVariable"
+        return "NonFixed: $originalTypeVariable${if (isMarkedNullable) "?" else ""}"
     }
 
     @TypeRefinement

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -81,7 +81,12 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
 
     override fun SimpleTypeMarker.isStubType(): Boolean {
         require(this is SimpleType, this::errorMessage)
-        return this is AbstractStubType
+        return this is StubType || this is StubTypeForProvideDelegateReceiver
+    }
+
+    override fun SimpleTypeMarker.isStubTypeForVariableInSubtyping(): Boolean {
+        require(this is SimpleType, this::errorMessage)
+        return this is StubTypeForTypeVariablesInSubtyping
     }
 
     override fun CapturedTypeMarker.lowerType(): KotlinTypeMarker? {
@@ -543,6 +548,10 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         errorSupportedOnlyInTypeInference()
     }
 
+    override fun createStubTypeForTypeVariablesInSubtyping(typeVariable: TypeVariableMarker): StubTypeMarker {
+        errorSupportedOnlyInTypeInference()
+    }
+
     override fun KotlinTypeMarker.isSpecial(): Boolean {
         require(this is KotlinType)
         return this is TypeUtils.SpecialType

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

@@ -136,6 +136,8 @@ class FlexibleTypeImpl(lowerBound: SimpleType, upperBound: SimpleType) : Flexibl
         return renderer.renderFlexibleType(renderer.renderType(lowerBound), renderer.renderType(upperBound), builtIns)
     }
 
+    override fun toString() = "($lowerBound..$upperBound)"
+
     override fun makeNullableAsSpecified(newNullability: Boolean): UnwrappedType = KotlinTypeFactory.flexibleType(
         lowerBound.makeNullableAsSpecified(newNullability),
         upperBound.makeNullableAsSpecified(newNullability)