Introduction of sealed classes

Sealed classes can be derived only by their own inner classes or objects.
Their constructors cannot be called explicitly, so compiler knows all their descendants.
Incompatible modifier checks (final, abstract). Impossible with interface, object, enum.
A pack of tests provided.

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

@@ -0,0 +1,9 @@
+sealed class Sealed(val x: Int) {
+    object First: Sealed(12)
+    open class NonFirst(x: Int, val y: Int): Sealed(x) {
+        object Second: NonFirst(34, 2)
+        object Third: NonFirst(56, 3)
+        // It's ALLOWED to inherit Sealed also here
+        object Fourth: Sealed(78)
+    }
+}

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

@@ -0,0 +1,52 @@
+package
+
+internal sealed class Sealed {
+    public constructor Sealed(/*0*/ x: kotlin.Int)
+    internal final val x: kotlin.Int
+    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
+
+    internal object First : Sealed {
+        private constructor First()
+        internal final override /*1*/ /*fake_override*/ val x: kotlin.Int
+        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
+    }
+
+    internal open class NonFirst : Sealed {
+        public constructor NonFirst(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.Int)
+        internal final override /*1*/ /*fake_override*/ val x: kotlin.Int
+        internal final val y: kotlin.Int
+        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
+
+        internal object Fourth : Sealed {
+            private constructor Fourth()
+            internal final override /*1*/ /*fake_override*/ val x: kotlin.Int
+            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
+        }
+
+        internal object Second : Sealed.NonFirst {
+            private constructor Second()
+            internal final override /*1*/ /*fake_override*/ val x: kotlin.Int
+            internal final override /*1*/ /*fake_override*/ val y: kotlin.Int
+            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
+        }
+
+        internal object Third : Sealed.NonFirst {
+            private constructor Third()
+            internal final override /*1*/ /*fake_override*/ val x: kotlin.Int
+            internal final override /*1*/ /*fake_override*/ val y: kotlin.Int
+            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
+        }
+    }
+}

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

@@ -0,0 +1,13 @@
+sealed class Sealed {
+    object First: Sealed()
+    open class NonFirst: Sealed() {
+        object Second: NonFirst()
+        object Third: NonFirst()
+        fun foo(): Int {
+            val s = object: <!SEALED_SUPERTYPE_IN_LOCAL_CLASS!>Sealed<!>() {}
+            class Local: <!SEALED_SUPERTYPE_IN_LOCAL_CLASS!>Sealed<!>() {}
+            return s.hashCode()
+        }
+    }
+    val p: Sealed = object: <!SEALED_SUPERTYPE_IN_LOCAL_CLASS!>Sealed<!>() {}
+}

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

@@ -0,0 +1,44 @@
+package
+
+internal sealed class Sealed {
+    public constructor Sealed()
+    internal final val p: Sealed
+    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
+
+    internal object First : Sealed {
+        private constructor First()
+        internal final override /*1*/ /*fake_override*/ val p: Sealed
+        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
+    }
+
+    internal open class NonFirst : Sealed {
+        public constructor NonFirst()
+        internal final override /*1*/ /*fake_override*/ val p: Sealed
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        internal final fun foo(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+        internal object Second : Sealed.NonFirst {
+            private constructor Second()
+            internal final override /*1*/ /*fake_override*/ val p: Sealed
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            internal final override /*1*/ /*fake_override*/ fun foo(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
+
+        internal object Third : Sealed.NonFirst {
+            private constructor Third()
+            internal final override /*1*/ /*fake_override*/ val p: Sealed
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            internal final override /*1*/ /*fake_override*/ fun foo(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
+    }
+}

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

@@ -0,0 +1,3 @@
+sealed class Base {
+    fun foo() = <!SEALED_CLASS_CONSTRUCTOR_CALL!>Base()<!>
+}

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

@@ -0,0 +1,9 @@
+package
+
+internal sealed class Base {
+    public constructor Base()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal final fun foo(): Base
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

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

@@ -0,0 +1,7 @@
+sealed class Base {
+
+}
+
+class Derived: <!SEALED_SUPERTYPE!>Base<!>() {
+
+}

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

@@ -0,0 +1,15 @@
+package
+
+internal sealed class Base {
+    public 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
+}
+
+internal final class Derived : Base {
+    public constructor Derived()
+    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
+}

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

@@ -0,0 +1,6 @@
+<!SEALED_MODIFIER_IN_ENUM!>sealed<!> enum class SealedEnum {
+    FIRST, 
+    SECOND;
+
+    class Derived: SealedEnum()
+}

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

@@ -0,0 +1,45 @@
+package
+
+internal sealed enum class SealedEnum : kotlin.Enum<SealedEnum> {
+    public enum entry FIRST : SealedEnum {
+        private constructor FIRST()
+        public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: SealedEnum): kotlin.Int
+        public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public final override /*1*/ /*fake_override*/ fun name(): kotlin.String
+        public final override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    public enum entry SECOND : SealedEnum {
+        private constructor SECOND()
+        public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: SealedEnum): kotlin.Int
+        public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public final override /*1*/ /*fake_override*/ fun name(): kotlin.String
+        public final override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    private constructor SealedEnum()
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: SealedEnum): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun name(): kotlin.String
+    public final override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    internal final class Derived : SealedEnum {
+        public constructor Derived()
+        public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: SealedEnum): kotlin.Int
+        public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public final override /*1*/ /*fake_override*/ fun name(): kotlin.String
+        public final override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): SealedEnum
+    public final /*synthesized*/ fun values(): kotlin.Array<SealedEnum>
+}

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

@@ -0,0 +1,3 @@
+<!FINAL_MODIFIER_IN_SEALED!>final<!> sealed class Base {
+
+}

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

@@ -0,0 +1,8 @@
+package
+
+internal sealed class Base {
+    public 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
+}

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

@@ -0,0 +1,3 @@
+<!TRAIT_CAN_NOT_BE_SEALED!>sealed<!> interface Base {
+
+}

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

@@ -0,0 +1,7 @@
+package
+
+internal sealed interface 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
+}

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

@@ -0,0 +1,3 @@
+<!ILLEGAL_MODIFIER!>sealed<!> object Sealed {
+
+}

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

@@ -0,0 +1,8 @@
+package
+
+internal object Sealed {
+    private constructor Sealed()
+    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
+}

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

@@ -0,0 +1,3 @@
+<!OPEN_MODIFIER_IN_SEALED!>open<!> sealed class Base {
+
+}

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

@@ -0,0 +1,8 @@
+package
+
+internal sealed class Base {
+    public 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
+}

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

@@ -0,0 +1,3 @@
+<!ABSTRACT_MODIFIER_IN_SEALED!>abstract<!> sealed class Base {
+
+}

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

@@ -0,0 +1,8 @@
+package
+
+internal sealed class Base {
+    public 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
+}