[FE] Allow declaring protected constructors in sealed classes

#KT-44865 Fixed

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java

@@ -24511,6 +24511,18 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/sealed/OperationWhen.kt");
             }
 
+            @Test
+            @TestMetadata("protectedConstructors_disabled.kt")
+            public void testProtectedConstructors_disabled() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/sealed/protectedConstructors_disabled.kt");
+            }
+
+            @Test
+            @TestMetadata("protectedConstructors_enabled.kt")
+            public void testProtectedConstructors_enabled() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/sealed/protectedConstructors_enabled.kt");
+            }
+
             @Test
             @TestMetadata("RedundantAbstract.kt")
             public void testRedundantAbstract() throws Exception {

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

@@ -346,6 +346,7 @@ public interface Errors {
 
     DiagnosticFactory0<PsiElement> NON_PRIVATE_CONSTRUCTOR_IN_ENUM = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> NON_PRIVATE_CONSTRUCTOR_IN_SEALED = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED = DiagnosticFactory0.create(ERROR);
 
     // Inline and value classes
 

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

@@ -705,6 +705,7 @@ public class DefaultErrorMessages {
 
         MAP.put(NON_PRIVATE_CONSTRUCTOR_IN_ENUM, "Constructor must be private in enum class");
         MAP.put(NON_PRIVATE_CONSTRUCTOR_IN_SEALED, "Constructor must be private in sealed class");
+        MAP.put(NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED, "Constructor must be private or protected in sealed class");
 
         MAP.put(INLINE_CLASS_NOT_TOP_LEVEL, "Inline classes cannot be local or inner");
         MAP.put(INLINE_CLASS_NOT_FINAL, "Inline classes can be only final");

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

@@ -289,12 +289,22 @@ class DeclarationsChecker(
 
     private fun checkConstructorVisibility(constructorDescriptor: ClassConstructorDescriptor, declaration: KtDeclaration) {
         val visibilityModifier = declaration.visibilityModifier()
-        if (visibilityModifier != null && visibilityModifier.node?.elementType != KtTokens.PRIVATE_KEYWORD) {
+        val visibilityKeyword = visibilityModifier?.node?.elementType ?: return
         val classDescriptor = constructorDescriptor.containingDeclaration
-            if (classDescriptor.kind == ClassKind.ENUM_CLASS) {
+
+        when {
+            classDescriptor.kind == ClassKind.ENUM_CLASS -> {
+                if (visibilityKeyword != KtTokens.PRIVATE_KEYWORD) {
                     trace.report(NON_PRIVATE_CONSTRUCTOR_IN_ENUM.on(visibilityModifier))
-            } else if (classDescriptor.modality == Modality.SEALED) {
-                trace.report(NON_PRIVATE_CONSTRUCTOR_IN_SEALED.on(visibilityModifier))
+                }
+            }
+            classDescriptor.modality == Modality.SEALED -> {
+                val protectedIsAllowed =
+                    languageVersionSettings.supportsFeature(LanguageFeature.AllowSealedInheritorsInDifferentFilesOfSamePackage)
+                if (!(visibilityKeyword == KtTokens.PRIVATE_KEYWORD || (protectedIsAllowed && visibilityKeyword == KtTokens.PROTECTED_KEYWORD))) {
+                    val factory = if (protectedIsAllowed) NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED else NON_PRIVATE_CONSTRUCTOR_IN_SEALED
+                    trace.report(factory.on(visibilityModifier))
+                }
             }
         }
     }

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

-sealed class Sealed <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(val x: Int) {
+sealed class Sealed protected constructor(val x: Int) {
     object FIRST : Sealed()
 
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>public<!> constructor(): this(42)
+    <!NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED!>public<!> constructor(): this(42)
 
     constructor(y: Int, z: Int): this(y + z)
 }

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

+// LANGUAGE: -AllowSealedInheritorsInDifferentFilesOfSamePackage
+// DIAGNOSTICS: -UNUSED_PARAMETER
+
+sealed class Case1(val x: Int) {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case1(10)
+    class Inheritor2 : Case1("Hello")
+}
+
+sealed class Case2 <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(val x: Int)<!> {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case2(10)
+    class Inheritor2 : Case2("Hello")
+}
+
+sealed class Case3 private constructor(val x: Int) {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case3(10) // should OK
+    class Inheritor2 : Case3("Hello")
+}
+
+class Case3Inheritor3 : <!INAPPLICABLE_CANDIDATE!>Case3<!>(20) // should be an error in 1.6 (?)
+
+sealed class Case4 {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(x: Int)<!>
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case4(10)
+    class Inheritor2 : Case4("Hello")
+}
+
+sealed class Case5() {
+    private constructor(x: Int) : this()
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(x: Byte) : this()<!>
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>internal constructor(x: Short) : this()<!>
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>public constructor(x: Long) : this()<!>
+    constructor(x: Double) : this()
+}

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

+// LANGUAGE: -AllowSealedInheritorsInDifferentFilesOfSamePackage
+// DIAGNOSTICS: -UNUSED_PARAMETER
+
+sealed class Case1(val x: Int) {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case1(10)
+    class Inheritor2 : Case1("Hello")
+}
+
+sealed class Case2 <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(val x: Int) {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case2(10)
+    class Inheritor2 : Case2("Hello")
+}
+
+sealed class Case3 private constructor(val x: Int) {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case3(10) // should OK
+    class Inheritor2 : Case3("Hello")
+}
+
+class Case3Inheritor3 : Case3(20) // should be an error in 1.6 (?)
+
+sealed class Case4 {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(x: Int)
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case4(10)
+    class Inheritor2 : Case4("Hello")
+}
+
+sealed class Case5() {
+    private constructor(x: Int) : this()
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected<!> constructor(x: Byte) : this()
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>internal<!> constructor(x: Short) : this()
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>public<!> constructor(x: Long) : this()
+    constructor(x: Double) : this()
+}

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

+package
+
+public sealed class Case1 {
+    private constructor Case1(/*0*/ x: kotlin.Int)
+    protected constructor Case1(/*0*/ s: kotlin.String)
+    public 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
+
+    public final class Inheritor1 : Case1 {
+        public constructor Inheritor1()
+        public 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
+    }
+
+    public final class Inheritor2 : Case1 {
+        public constructor Inheritor2()
+        public 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
+    }
+}
+
+public sealed class Case2 {
+    protected constructor Case2(/*0*/ x: kotlin.Int)
+    protected constructor Case2(/*0*/ s: kotlin.String)
+    public 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
+
+    public final class Inheritor1 : Case2 {
+        public constructor Inheritor1()
+        public 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
+    }
+
+    public final class Inheritor2 : Case2 {
+        public constructor Inheritor2()
+        public 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
+    }
+}
+
+public sealed class Case3 {
+    private constructor Case3(/*0*/ x: kotlin.Int)
+    protected constructor Case3(/*0*/ s: kotlin.String)
+    public 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
+
+    public final class Inheritor1 : Case3 {
+        public constructor Inheritor1()
+        public 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
+    }
+
+    public final class Inheritor2 : Case3 {
+        public constructor Inheritor2()
+        public 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
+    }
+}
+
+public final class Case3Inheritor3 : Case3 {
+    public constructor Case3Inheritor3()
+    public 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
+}
+
+public sealed class Case4 {
+    protected constructor Case4(/*0*/ x: kotlin.Int)
+    protected constructor Case4(/*0*/ s: kotlin.String)
+    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 Inheritor1 : Case4 {
+        public constructor Inheritor1()
+        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 Inheritor2 : Case4 {
+        public constructor Inheritor2()
+        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 sealed class Case5 {
+    private constructor Case5()
+    protected constructor Case5(/*0*/ x: kotlin.Byte)
+    private constructor Case5(/*0*/ x: kotlin.Double)
+    private constructor Case5(/*0*/ x: kotlin.Int)
+    public constructor Case5(/*0*/ x: kotlin.Long)
+    internal constructor Case5(/*0*/ x: kotlin.Short)
+    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/protectedConstructors_enabled.fir.kt

+// LANGUAGE: +AllowSealedInheritorsInDifferentFilesOfSamePackage
+// DIAGNOSTICS: -UNUSED_PARAMETER
+
+sealed class Case1(val x: Int) {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case1(10)
+    class Inheritor2 : Case1("Hello")
+}
+
+sealed class Case2 <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(val x: Int)<!> { // should be REDUNDANT_MODIFIER
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case2(10)
+    class Inheritor2 : Case2("Hello")
+}
+
+sealed class Case3 private constructor(val x: Int) {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case3(10) // should OK
+    class Inheritor2 : Case3("Hello")
+}
+
+class Case3Inheritor3 : <!INAPPLICABLE_CANDIDATE!>Case3<!>(20) // should be an error in 1.6 (?)
+
+sealed class Case4 {
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(x: Int)<!>
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+
+    class Inheritor1 : Case4(10)
+    class Inheritor2 : Case4("Hello")
+}
+
+sealed class Case5() {
+    private constructor(x: Int) : this()
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(x: Byte) : this()<!>
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>internal constructor(x: Short) : this()<!>
+    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>public constructor(x: Long) : this()<!>
+    constructor(x: Double) : this()
+}

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

+// LANGUAGE: +AllowSealedInheritorsInDifferentFilesOfSamePackage
+// DIAGNOSTICS: -UNUSED_PARAMETER
+
+sealed class Case1(val x: Int) {
+    protected constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case1(10)
+    class Inheritor2 : Case1("Hello")
+}
+
+sealed class Case2 protected constructor(val x: Int) { // should be REDUNDANT_MODIFIER
+    protected constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case2(10)
+    class Inheritor2 : Case2("Hello")
+}
+
+sealed class Case3 private constructor(val x: Int) {
+    protected constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case3(10) // should OK
+    class Inheritor2 : Case3("Hello")
+}
+
+class Case3Inheritor3 : Case3(20) // should be an error in 1.6 (?)
+
+sealed class Case4 {
+    protected constructor(x: Int)
+    protected constructor(s: String) : this(s.length)
+
+    class Inheritor1 : Case4(10)
+    class Inheritor2 : Case4("Hello")
+}
+
+sealed class Case5() {
+    private constructor(x: Int) : this()
+    protected constructor(x: Byte) : this()
+    <!NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED!>internal<!> constructor(x: Short) : this()
+    <!NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED!>public<!> constructor(x: Long) : this()
+    constructor(x: Double) : this()
+}

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

+package
+
+public sealed class Case1 {
+    protected constructor Case1(/*0*/ x: kotlin.Int)
+    protected constructor Case1(/*0*/ s: kotlin.String)
+    public 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
+
+    public final class Inheritor1 : Case1 {
+        public constructor Inheritor1()
+        public 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
+    }
+
+    public final class Inheritor2 : Case1 {
+        public constructor Inheritor2()
+        public 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
+    }
+}
+
+public sealed class Case2 {
+    protected constructor Case2(/*0*/ x: kotlin.Int)
+    protected constructor Case2(/*0*/ s: kotlin.String)
+    public 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
+
+    public final class Inheritor1 : Case2 {
+        public constructor Inheritor1()
+        public 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
+    }
+
+    public final class Inheritor2 : Case2 {
+        public constructor Inheritor2()
+        public 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
+    }
+}
+
+public sealed class Case3 {
+    private constructor Case3(/*0*/ x: kotlin.Int)
+    protected constructor Case3(/*0*/ s: kotlin.String)
+    public 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
+
+    public final class Inheritor1 : Case3 {
+        public constructor Inheritor1()
+        public 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
+    }
+
+    public final class Inheritor2 : Case3 {
+        public constructor Inheritor2()
+        public 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
+    }
+}
+
+public final class Case3Inheritor3 : Case3 {
+    public constructor Case3Inheritor3()
+    public 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
+}
+
+public sealed class Case4 {
+    protected constructor Case4(/*0*/ x: kotlin.Int)
+    protected constructor Case4(/*0*/ s: kotlin.String)
+    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 Inheritor1 : Case4 {
+        public constructor Inheritor1()
+        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 Inheritor2 : Case4 {
+        public constructor Inheritor2()
+        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 sealed class Case5 {
+    protected constructor Case5()
+    protected constructor Case5(/*0*/ x: kotlin.Byte)
+    protected constructor Case5(/*0*/ x: kotlin.Double)
+    private constructor Case5(/*0*/ x: kotlin.Int)
+    public constructor Case5(/*0*/ x: kotlin.Long)
+    internal constructor Case5(/*0*/ x: kotlin.Short)
+    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/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -24601,6 +24601,18 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/sealed/OperationWhen.kt");
             }
 
+            @Test
+            @TestMetadata("protectedConstructors_disabled.kt")
+            public void testProtectedConstructors_disabled() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/sealed/protectedConstructors_disabled.kt");
+            }
+
+            @Test
+            @TestMetadata("protectedConstructors_enabled.kt")
+            public void testProtectedConstructors_enabled() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/sealed/protectedConstructors_enabled.kt");
+            }
+
             @Test
             @TestMetadata("RedundantAbstract.kt")
             public void testRedundantAbstract() throws Exception {

idea/src/org/jetbrains/kotlin/idea/quickfix/QuickFixRegistrar.kt

@@ -149,6 +149,7 @@ class QuickFixRegistrar : QuickFixContributor {
         REPEATED_MODIFIER.registerFactory(removeModifierFactory)
         NON_PRIVATE_CONSTRUCTOR_IN_ENUM.registerFactory(removeModifierFactory)
         NON_PRIVATE_CONSTRUCTOR_IN_SEALED.registerFactory(removeModifierFactory)
+        NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED.registerFactory(removeModifierFactory)
         TYPE_CANT_BE_USED_FOR_CONST_VAL.registerFactory(removeModifierFactory)
         DEPRECATED_BINARY_MOD.registerFactory(removeModifierFactory)
         DEPRECATED_BINARY_MOD.registerFactory(RenameModToRemFix.Factory)