KT-6803 Subtyping breaks on star-projections for recursive generics

Star-projections have upper bounds of the form "parameter's bound where all parameter of the same class are substituted with their star-projections"

  #KT-6803 Fixed

core/descriptors/src/org/jetbrains/kotlin/types/CommonSupertypes.java

@@ -69,6 +69,10 @@ public class CommonSupertypes {
         return 1 + maxDepth(KotlinPackage.map(type.getArguments(), new Function1<TypeProjection, JetType>() {
             @Override
             public JetType invoke(TypeProjection projection) {
+                if (projection.isStarProjection()) {
+                    // any type is good enough for depth here
+                    return KotlinBuiltIns.getInstance().getAnyType();
+                }
                 return projection.getType();
             }
         }));

core/descriptors/src/org/jetbrains/kotlin/types/ErrorUtils.java

@@ -377,7 +377,7 @@ public class ErrorUtils {
         if (type == null) return false;
         if (type.isError()) return true;
         for (TypeProjection projection : type.getArguments()) {
-            if (containsErrorType(projection.getType())) return true;
+            if (!projection.isStarProjection() && containsErrorType(projection.getType())) return true;
         }
         return false;
     }

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

@@ -16,9 +16,35 @@
 
 package org.jetbrains.kotlin.types
 
-import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
+import kotlin.properties.*
+import org.jetbrains.kotlin.descriptors.*
 
 class StarProjectionImpl(
+        private val typeParameter: TypeParameterDescriptor
+) : TypeProjectionBase() {
+    override fun isStarProjection() = true
+
+    override fun getProjectionKind() = Variance.OUT_VARIANCE
+
+    private val _type: JetType by Delegates.lazy {
+        val classDescriptor = typeParameter.getContainingDeclaration() as ClassDescriptor
+        val typeParameters = classDescriptor.getTypeConstructor().getParameters().map { it.getTypeConstructor() }
+        TypeSubstitutor.create(
+                object : TypeSubstitution() {
+                    override fun get(key: TypeConstructor) = when (key) {
+                        typeParameter.getTypeConstructor() -> this@StarProjectionImpl
+                        in typeParameters -> TypeUtils.makeStarProjection(key.getDeclarationDescriptor() as TypeParameterDescriptor)
+                        else -> null
+                    }
+
+                }
+        ).substitute(typeParameter.getUpperBounds().iterator().next(), Variance.OUT_VARIANCE)!!
+    }
+
+    override fun getType() = _type
+}
+
+class TypeBasedStarProjectionImpl(
         private val _type: JetType
 ) : TypeProjectionBase() {
     override fun isStarProjection() = true

core/descriptors/src/org/jetbrains/kotlin/types/TypeProjectionBase.java

@@ -45,7 +45,7 @@ public abstract class TypeProjectionBase implements TypeProjection {
     @Override
     public int hashCode() {
         int result = getProjectionKind().hashCode();
-        result = 31 * result + (getType().hashCode());
+        result = 31 * result + (isStarProjection() ? 17 : getType().hashCode());
         return result;
     }
 }

core/descriptors/src/org/jetbrains/kotlin/types/TypeSubstitutor.java

@@ -213,6 +213,9 @@ public class TypeSubstitutor {
             if (typeVariable != null) {
                 substitutedType = typeVariable.substitutionResult(replacement.getType());
             }
+            else if (replacement.isStarProjection()) {
+                return replacement;
+            }
             else {
                 // this is a simple type T or T?: if it's T, we should just take replacement, if T? - we make replacement nullable
                 substitutedType = TypeUtils.makeNullableIfNeeded(replacement.getType(), type.isMarkedNullable());

core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.java

@@ -549,7 +549,7 @@ public class TypeUtils {
     public static boolean dependsOnTypeConstructors(@NotNull JetType type, @NotNull Collection<TypeConstructor> typeParameterConstructors) {
         if (typeParameterConstructors.contains(type.getConstructor())) return true;
         for (TypeProjection typeProjection : type.getArguments()) {
-            if (dependsOnTypeConstructors(typeProjection.getType(), typeParameterConstructors)) {
+            if (!typeProjection.isStarProjection() && dependsOnTypeConstructors(typeProjection.getType(), typeParameterConstructors)) {
                 return true;
             }
         }
@@ -577,14 +577,14 @@ public class TypeUtils {
             return true;
         }
         for (TypeProjection projection : type.getArguments()) {
-            if (containsSpecialType(projection.getType(), isSpecialType)) return true;
+            if (!projection.isStarProjection() && containsSpecialType(projection.getType(), isSpecialType)) return true;
         }
         return false;
     }
 
     @NotNull
     public static TypeProjection makeStarProjection(@NotNull TypeParameterDescriptor parameterDescriptor) {
-        return new StarProjectionImpl(parameterDescriptor.getUpperBoundsAsType());
+        return new StarProjectionImpl(parameterDescriptor);
     }
 
     @Nullable

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

@@ -33,7 +33,7 @@ import org.jetbrains.kotlin.types.TypeProjectionImpl
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.types.DelegatingType
 
-fun JetType.getContainedTypeParameters(): Collection<TypeParameterDescriptor> {
+private fun JetType.getContainedTypeParameters(): Collection<TypeParameterDescriptor> {
     val declarationDescriptor = getConstructor().getDeclarationDescriptor()
     if (declarationDescriptor is TypeParameterDescriptor) return listOf(declarationDescriptor)
 
@@ -41,7 +41,7 @@ fun JetType.getContainedTypeParameters(): Collection<TypeParameterDescriptor> {
     if (flexibility != null) {
         return flexibility.lowerBound.getContainedTypeParameters() + flexibility.upperBound.getContainedTypeParameters()
     }
-    return getArguments().map { it.getType() }.flatMap { it.getContainedTypeParameters() }
+    return getArguments().filter { !it.isStarProjection() }.map { it.getType() }.flatMap { it.getContainedTypeParameters() }
 }
 
 fun DeclarationDescriptor.getCapturedTypeParameters(): Collection<TypeParameterDescriptor> {

core/descriptors/src/org/jetbrains/kotlin/types/checker/TypeCheckingProcedure.java

@@ -106,6 +106,10 @@ public class TypeCheckingProcedure {
             TypeProjection typeProjection1 = type1Arguments.get(i);
             TypeParameterDescriptor typeParameter2 = constructor2.getParameters().get(i);
             TypeProjection typeProjection2 = type2Arguments.get(i);
+            if (typeProjection1.isStarProjection() && typeProjection2.isStarProjection()) {
+                continue;
+            }
+
             if (capture(typeProjection1, typeProjection2, typeParameter1)) {
                 continue;
             }
@@ -227,14 +231,16 @@ public class TypeCheckingProcedure {
         for (int i = 0; i < parameters.size(); i++) {
             TypeParameterDescriptor parameter = parameters.get(i);
 
+            TypeProjection superArgument = superArguments.get(i);
+            if (superArgument.isStarProjection()) continue;
+
+            JetType superIn = getInType(parameter, superArgument);
+            JetType superOut = getOutType(parameter, superArgument);
+
             TypeProjection subArgument = subArguments.get(i);
             JetType subIn = getInType(parameter, subArgument);
             JetType subOut = getOutType(parameter, subArgument);
 
-            TypeProjection superArgument = superArguments.get(i);
-            JetType superIn = getInType(parameter, superArgument);
-            JetType superOut = getOutType(parameter, superArgument);
-
             if (capture(subArgument, superArgument, parameter)) continue;
 
             boolean argumentIsErrorType = subArgument.getType().isError() || superArgument.getType().isError();

core/serialization/src/org/jetbrains/kotlin/serialization/deserialization/TypeDeserializer.kt

@@ -103,7 +103,7 @@ public class TypeDeserializer(
             protos.map { proto ->
                 val type = type(proto.getType())
                 if (proto.getProjection() == ProtoBuf.Type.Argument.Projection.STAR)
-                    StarProjectionImpl(type)
+                    TypeBasedStarProjectionImpl(type)
                 else TypeProjectionImpl(variance(proto.getProjection()), type)
             }.toReadOnlyList()