[FE] Prohibit inheritors of sealed classes which are declared in different package

#KT-13495

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -426,6 +426,7 @@ public interface Errors {
     DiagnosticFactory0<KtCallExpression> SEALED_CLASS_CONSTRUCTOR_CALL = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtTypeReference> SEALED_SUPERTYPE = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtTypeReference> SEALED_SUPERTYPE_IN_LOCAL_CLASS = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory2<KtTypeReference, FqName, FqName> SEALED_INHERITOR_IN_DIFFERENT_PACKAGE = DiagnosticFactory2.create(ERROR);
 
     // Companion objects
 

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -633,6 +633,7 @@ public class DefaultErrorMessages {
         MAP.put(DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES, "Data class inheritance from other classes is forbidden");
         MAP.put(SEALED_SUPERTYPE, "This type is sealed, so it can be inherited by only its own nested classes or objects");
         MAP.put(SEALED_SUPERTYPE_IN_LOCAL_CLASS, "Local class cannot extend a sealed class");
+        MAP.put(SEALED_INHERITOR_IN_DIFFERENT_PACKAGE, "Inheritor of sealed class or interface declared in package {1} but it must be in package {2} where base class is declared", TO_STRING, TO_STRING);
         MAP.put(SINGLETON_IN_SUPERTYPE, "Cannot inherit from a singleton");
         MAP.put(CLASS_CANNOT_BE_EXTENDED_DIRECTLY, "Class {0} cannot be extended directly", NAME);
 

compiler/frontend/src/org/jetbrains/kotlin/resolve/PlatformConfiguratorBase.kt

@@ -40,7 +40,8 @@ private val DEFAULT_DECLARATION_CHECKERS = listOf(
     FunInterfaceDeclarationChecker(),
     DeprecatedSinceKotlinAnnotationChecker,
     ContractDescriptionBlockChecker,
-    PrivateInlineFunctionsReturningAnonymousObjectsChecker
+    PrivateInlineFunctionsReturningAnonymousObjectsChecker,
+    SealedInheritorInSamePackageChecker,
 )
 
 private val DEFAULT_CALL_CHECKERS = listOf(

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/SealedInheritorInSamePackageChecker.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.resolve.checkers
+
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.containingPackage
+import org.jetbrains.kotlin.descriptors.isSealed
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.psi.KtClassOrObject
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.resolve.bindingContextUtil.getAbbreviatedTypeOrType
+
+object SealedInheritorInSamePackageChecker : DeclarationChecker {
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (!context.languageVersionSettings.supportsFeature(LanguageFeature.FreedomForSealedClasses)) return
+        if (descriptor !is ClassDescriptor || declaration !is KtClassOrObject) return
+        val classPackage = descriptor.containingPackage() ?: return // local class, SEALED_SUPERTYPE already reported
+        for (superTypeListEntry in declaration.superTypeListEntries) {
+            val typeReference = superTypeListEntry.typeReference ?: continue
+            val superType = typeReference.getAbbreviatedTypeOrType(context.trace.bindingContext)?.unwrap() ?: continue
+            val superClass = superType.constructor.declarationDescriptor ?: continue
+            if (!superClass.isSealed()) continue
+            val superClassPackage = superClass.containingPackage() ?: continue
+            if (classPackage != superClassPackage) {
+                context.trace.report(Errors.SEALED_INHERITOR_IN_DIFFERENT_PACKAGE.on(typeReference, classPackage, superClassPackage))
+            }
+        }
+    }
+}

compiler/testData/diagnostics/tests/sealed/MultipleFiles_enabled.fir.kt

@@ -3,16 +3,22 @@
 
 // FILE: a.kt
 
+package foo
+
 sealed class Base {
     class A : Base()
 }
 
 // FILE: b.kt
 
+package foo
+
 class B : <!HIDDEN!>Base<!>()
 
 // FILE: c.kt
 
+package foo
+
 class Container {
     class C : <!HIDDEN, SEALED_SUPERTYPE!>Base<!>()
 
@@ -24,3 +30,11 @@ class Container {
         class LocalClass : <!HIDDEN, SEALED_SUPERTYPE_IN_LOCAL_CLASS!>Base<!>() {} // Should be an error
     }
 }
+
+// FILE: E.kt
+
+package bar
+
+import foo.Base
+
+class E : <!HIDDEN!>Base<!>()

compiler/testData/diagnostics/tests/sealed/MultipleFiles_enabled.kt

@@ -3,16 +3,22 @@
 
 // FILE: a.kt
 
+package foo
+
 sealed class Base {
     class A : Base()
 }
 
 // FILE: b.kt
 
+package foo
+
 class B : Base()
 
 // FILE: c.kt
 
+package foo
+
 class Container {
     class C : Base()
 
@@ -24,3 +30,11 @@ class Container {
         class LocalClass : <!SEALED_SUPERTYPE!>Base<!>() {} // Should be an error
     }
 }
+
+// FILE: E.kt
+
+package bar
+
+import foo.Base
+
+class E : <!SEALED_INHERITOR_IN_DIFFERENT_PACKAGE!>Base<!>()

compiler/testData/diagnostics/tests/sealed/MultipleFiles_enabled.txt

@@ -1,45 +1,58 @@
 package
 
-public final class B : Base {
-    public constructor B()
-    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
-}
+package bar {
 
-public sealed class Base {
-    internal constructor Base()
-    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
-
-    public final class A : Base {
-        public constructor A()
+    public final class E : foo.Base {
+        public constructor E()
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
         public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
     }
 }
 
-public final class Container {
-    public constructor Container()
-    public final val anon: Base
-    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public final fun someFun(): kotlin.Unit
-    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+package foo {
 
-    public final class C : Base {
-        public constructor C()
+    public final class B : foo.Base {
+        public constructor B()
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
         public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
     }
 
-    public final inner class D : Base {
-        public constructor D()
+    public sealed class Base {
+        internal constructor Base()
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
         public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+        public final class A : foo.Base {
+            public constructor A()
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
+    }
+
+    public final class Container {
+        public constructor Container()
+        public final val anon: foo.Base
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public final fun someFun(): kotlin.Unit
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+        public final class C : foo.Base {
+            public constructor C()
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
+
+        public final inner class D : foo.Base {
+            public constructor D()
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
     }
 }

core/descriptors/src/org/jetbrains/kotlin/descriptors/descriptorUtil.kt

@@ -10,11 +10,14 @@ import org.jetbrains.kotlin.builtins.StandardNames.CONTINUATION_INTERFACE_FQ_NAM
 import org.jetbrains.kotlin.incremental.components.LookupLocation
 import org.jetbrains.kotlin.incremental.components.NoLookupLocation
 import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.KotlinTypeFactory
 import org.jetbrains.kotlin.types.typeUtil.asTypeProjection
 import org.jetbrains.kotlin.utils.sure
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 
 fun ModuleDescriptor.resolveClassByFqName(fqName: FqName, lookupLocation: LookupLocation): ClassDescriptor? {
     if (fqName.isRoot) return null
@@ -56,3 +59,21 @@ fun DeclarationDescriptor.isTopLevelInPackage(name: String, packageName: String)
 }
 
 fun CallableDescriptor.isSupportedForCallableReference() = this is PropertyDescriptor || this is FunctionDescriptor
+
+@OptIn(ExperimentalContracts::class)
+fun DeclarationDescriptor.isSealed(): Boolean {
+    contract {
+        returns(true) implies (this@isSealed is ClassDescriptor)
+    }
+    return DescriptorUtils.isSealedClass(this)
+}
+
+fun DeclarationDescriptor.containingPackage(): FqName? {
+    var container = containingDeclaration
+    while (true) {
+        if (container == null || container is PackageFragmentDescriptor) break
+        container = container.containingDeclaration
+    }
+    require(container is PackageFragmentDescriptor?)
+    return container?.fqName
+}