[FIR] Fix processing constructors of sealed classes

- Allow declaring protected constructors in sealed classes
- Make default visibility of sealed class constructor `protected`

KT-44861
KT-44865

compiler/fir/analysis-tests/testData/loadCompiledKotlin/annotations/classMembers/HiddenConstructorWithInlineClassParameters.txt

@@ -12,7 +12,7 @@ public sealed class Sealed : R|kotlin/Any| {
     public final val z: R|test/Z|
         public get(): R|test/Z|
 
-    @R|test/Ann|() internal constructor(@R|test/Ann|() z: R|test/Z|): R|test/Sealed|
+    @R|test/Ann|() protected constructor(@R|test/Ann|() z: R|test/Z|): R|test/Sealed|
 
 }
 

compiler/fir/analysis-tests/testData/loadCompiledKotlin/class/SealedClass.txt

@@ -14,7 +14,7 @@ public sealed class SealedClass : R|kotlin/Any| {
 
     }
 
-    internal constructor(): R|test/SealedClass|
+    protected constructor(): R|test/SealedClass|
 
 }
 

compiler/fir/analysis-tests/testData/resolve/constantValues.fir.txt

@@ -44,7 +44,7 @@ FILE: constantValues.kt
         }
 
         public sealed class Value : R|kotlin/Any| {
-            private constructor(): R|KClassValue.Value| {
+            protected constructor(): R|KClassValue.Value| {
                 super<R|kotlin/Any|>()
             }
 

compiler/fir/analysis-tests/testData/resolve/diagnostics/incompatibleModifiers.fir.txt

@@ -30,13 +30,13 @@ FILE: incompatibleModifiers.kt
 
     }
     public final class F : R|kotlin/Any| {
-        private constructor(): R|F| {
+        protected constructor(): R|F| {
             super<R|kotlin/Any|>()
         }
 
     }
     public sealed class G : R|kotlin/Any| {
-        private constructor(): R|G| {
+        protected constructor(): R|G| {
             super<R|kotlin/Any|>()
         }
 
@@ -57,7 +57,7 @@ FILE: incompatibleModifiers.kt
 
     }
     public sealed data class I : R|kotlin/Any| {
-        private constructor(i: R|kotlin/Int|): R|I| {
+        protected constructor(i: R|kotlin/Int|): R|I| {
             super<R|kotlin/Any|>()
         }
 
@@ -126,7 +126,7 @@ FILE: incompatibleModifiers.kt
         }
 
         public sealed inner class Z : R|kotlin/Any| {
-            private constructor(): R|X.Z| {
+            protected constructor(): R|X.Z| {
                 super<R|kotlin/Any|>()
             }
 

compiler/fir/analysis-tests/testData/resolve/diagnostics/redundantModifier.fir.txt

@@ -6,7 +6,7 @@ FILE: redundantModifier.kt
 
     }
     public sealed class B : R|kotlin/Any| {
-        private constructor(): R|B| {
+        protected constructor(): R|B| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/diagnostics/sealedClassConstructorCall.fir.txt

 FILE: sealedClassConstructorCall.kt
     public sealed class A : R|kotlin/Any| {
-        private constructor(): R|A| {
+        protected constructor(): R|A| {
             super<R|kotlin/Any|>()
         }
 
     }
-    public final val b: R|A| = R|/A.A|()
+    public final val b: R|A| = <HIDDEN: /A.A is invisible>#()
         public get(): R|A|

compiler/fir/analysis-tests/testData/resolve/diagnostics/sealedClassConstructorCall.kt

 sealed class A
 
-val b = <!SEALED_CLASS_CONSTRUCTOR_CALL{LT}!><!SEALED_CLASS_CONSTRUCTOR_CALL{PSI}!>A<!>()<!>
+val b = <!HIDDEN{LT}!><!HIDDEN{PSI}!>A<!>()<!>

compiler/fir/analysis-tests/testData/resolve/diagnostics/sealedSupertype.fir.txt

 FILE: sealedSupertype.kt
     public sealed class A : R|kotlin/Any| {
-        private constructor(): R|A| {
+        protected constructor(): R|A| {
             super<R|kotlin/Any|>()
         }
 
@@ -22,7 +22,7 @@ FILE: sealedSupertype.kt
 
     }
     public sealed class P : R|kotlin/Any| {
-        private constructor(): R|P| {
+        protected constructor(): R|P| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/exhaustiveness/negative/missingSealedInheritor.fir.txt

 FILE: a.kt
     public sealed class Base : R|kotlin/Any| {
-        private constructor(): R|Base| {
+        protected constructor(): R|Base| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/exhaustiveness/positive/exhaustiveness_sealedClass.fir.txt

 FILE: exhaustiveness_sealedClass.kt
     public sealed class Base : R|kotlin/Any| {
-        private constructor(): R|Base| {
+        protected constructor(): R|Base| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/exhaustiveness/positive/exhaustiveness_sealedObject.fir.txt

 FILE: exhaustiveness_sealedObject.kt
     public sealed class A : R|kotlin/Any| {
-        private constructor(): R|A| {
+        protected constructor(): R|A| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/exhaustiveness/positive/exhaustiveness_sealedSubClass.fir.txt

 FILE: exhaustiveness_sealedSubClass.kt
     public sealed class A : R|kotlin/Any| {
-        private constructor(): R|A| {
+        protected constructor(): R|A| {
             super<R|kotlin/Any|>()
         }
 
     }
     public sealed class B : R|A| {
-        private constructor(): R|B| {
+        protected constructor(): R|B| {
             super<R|A|>()
         }
 
@@ -18,13 +18,13 @@ FILE: exhaustiveness_sealedSubClass.kt
 
     }
     public sealed class D : R|B| {
-        private constructor(): R|D| {
+        protected constructor(): R|D| {
             super<R|B|>()
         }
 
     }
     public sealed class E : R|B| {
-        private constructor(): R|E| {
+        protected constructor(): R|E| {
             super<R|B|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/expresssions/classifierAccessFromCompanion.fir.txt

@@ -5,7 +5,7 @@ FILE: classifierAccessFromCompanion.kt
         }
 
         public sealed class Function : R|kotlin/Any| {
-            private constructor(): R|Factory.Function| {
+            protected constructor(): R|Factory.Function| {
                 super<R|kotlin/Any|>()
             }
 

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/RedundantVisibilityModifierChecker.fir.txt

@@ -111,7 +111,7 @@ FILE: RedundantVisibilityModifierChecker.kt
 
     }
     public sealed class G : R|kotlin/Any| {
-        private constructor(y: R|kotlin/Int|): R|G| {
+        protected constructor(y: R|kotlin/Int|): R|G| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/multifile/sealedStarImport.fir.txt

 FILE: test.kt
     public sealed class Test : R|kotlin/Any| {
-        private constructor(): R|test/Test| {
+        protected constructor(): R|test/Test| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/recursiveCallOnWhenWithSealedClass.fir.txt

 FILE: recursiveCallOnWhenWithSealedClass.kt
     public sealed class Maybe<T> : R|kotlin/Any| {
-        private constructor<T>(): R|Maybe<T>| {
+        protected constructor<T>(): R|Maybe<T>| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/sealedClass.fir.txt

 FILE: sealedClass.kt
     public sealed class Foo : R|kotlin/Any| {
-        private constructor(value: R|kotlin/String|): R|Foo| {
+        protected constructor(value: R|kotlin/String|): R|Foo| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/smartcasts/kt37327.fir.txt

@@ -2,7 +2,7 @@ FILE: kt37327.kt
     public abstract interface Q : R|kotlin/Any| {
     }
     public sealed class A : R|Q| {
-        private constructor(): R|A| {
+        protected constructor(): R|A| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/smartcasts/lambdas/lambdaInWhenBranch.fir.txt

 FILE: lambdaInWhenBranch.kt
     private sealed class Sealed : R|kotlin/Any| {
-        private constructor(): R|Sealed| {
+        protected constructor(): R|Sealed| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/analysis-tests/testData/resolve/types/bareWithSubjectTypeAlias.fir.txt

 FILE: bareWithSubjectTypeAlias.kt
     public sealed class A<out T> : R|kotlin/Any| {
-        private constructor<out T>(): R|A<T>| {
+        protected constructor<out T>(): R|A<T>| {
             super<R|kotlin/Any|>()
         }
 

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -88,7 +88,7 @@ val DIAGNOSTICS_LIST = DiagnosticListBuilder.buildDiagnosticList {
         val CONSTRUCTOR_IN_OBJECT by error<FirSourceElement, KtDeclaration>(PositioningStrategy.DECLARATION_SIGNATURE)
         val CONSTRUCTOR_IN_INTERFACE by error<FirSourceElement, KtDeclaration>(PositioningStrategy.DECLARATION_SIGNATURE)
         val NON_PRIVATE_CONSTRUCTOR_IN_ENUM by error<FirSourceElement, PsiElement>()
-        val NON_PRIVATE_CONSTRUCTOR_IN_SEALED by error<FirSourceElement, PsiElement>()
+        val NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED by error<FirSourceElement, PsiElement>()
         val CYCLIC_CONSTRUCTOR_DELEGATION_CALL by warning<FirSourceElement, PsiElement>()
         val PRIMARY_CONSTRUCTOR_DELEGATION_CALL_EXPECTED by warning<FirSourceElement, PsiElement>(PositioningStrategy.SECONDARY_CONSTRUCTOR_DELEGATION_CALL)
         val SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR by warning<FirSourceElement, PsiElement>()

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -95,7 +95,7 @@ object FirErrors {
     val CONSTRUCTOR_IN_OBJECT by error0<FirSourceElement, KtDeclaration>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val CONSTRUCTOR_IN_INTERFACE by error0<FirSourceElement, KtDeclaration>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val NON_PRIVATE_CONSTRUCTOR_IN_ENUM by error0<FirSourceElement, PsiElement>()
-    val NON_PRIVATE_CONSTRUCTOR_IN_SEALED by error0<FirSourceElement, PsiElement>()
+    val NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED by error0<FirSourceElement, PsiElement>()
     val CYCLIC_CONSTRUCTOR_DELEGATION_CALL by warning0<FirSourceElement, PsiElement>()
     val PRIMARY_CONSTRUCTOR_DELEGATION_CALL_EXPECTED by warning0<FirSourceElement, PsiElement>(SourceElementPositioningStrategies.SECONDARY_CONSTRUCTOR_DELEGATION_CALL)
     val SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR by warning0<FirSourceElement, PsiElement>()

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConstructorAllowedChecker.kt

@@ -14,6 +14,8 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
+import org.jetbrains.kotlin.lexer.KtTokens
 
 object FirConstructorAllowedChecker : FirConstructorChecker() {
     override fun check(declaration: FirConstructor, context: CheckerContext, reporter: DiagnosticReporter) {
@@ -30,10 +32,14 @@ object FirConstructorAllowedChecker : FirConstructorChecker() {
             ClassKind.ENUM_CLASS -> if (declaration.visibility != Visibilities.Private) {
                 reporter.reportOn(source, FirErrors.NON_PRIVATE_CONSTRUCTOR_IN_ENUM, context)
             }
-            ClassKind.CLASS -> if (containingClass is FirRegularClass && containingClass.modality == Modality.SEALED &&
-                declaration.visibility != Visibilities.Private
-            ) {
-                reporter.reportOn(source, FirErrors.NON_PRIVATE_CONSTRUCTOR_IN_SEALED, context)
+            ClassKind.CLASS -> if (containingClass is FirRegularClass && containingClass.modality == Modality.SEALED) {
+                val modifierList = with(FirModifierList) { source.getModifierList() } ?: return
+                val hasIllegalModifier = modifierList.modifiers.any {
+                    it.token != KtTokens.PROTECTED_KEYWORD && it.token != KtTokens.PRIVATE_KEYWORD
+                }
+                if (hasIllegalModifier) {
+                    reporter.reportOn(source, FirErrors.NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED, context)
+                }
             }
             ClassKind.ANNOTATION_CLASS -> {
                 // DO NOTHING

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt

@@ -101,7 +101,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NONE_APPLICABLE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_ABSTRACT_FUNCTION_WITH_NO_BODY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_MEMBER_FUNCTION_NO_BODY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_PRIVATE_CONSTRUCTOR_IN_ENUM
-import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_PRIVATE_CONSTRUCTOR_IN_SEALED
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOTHING_TO_OVERRIDE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_AN_ANNOTATION_CLASS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_A_LOOP_LABEL
@@ -247,7 +247,7 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(CONSTRUCTOR_IN_OBJECT, "Constructors are not allowed for objects")
             map.put(CONSTRUCTOR_IN_INTERFACE, "An interface may not have a constructor")
             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(CYCLIC_CONSTRUCTOR_DELEGATION_CALL, "There's a cycle in the delegation calls chain")
             map.put(PRIMARY_CONSTRUCTOR_DELEGATION_CALL_EXPECTED, "Primary constructor call expected")
             map.put(SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR, "Supertype initialization is impossible without primary constructor")

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/DeclarationsConverter.kt

@@ -740,7 +740,9 @@ class DeclarationsConverter(
             extractArgumentsFrom(classWrapper.superTypeCallEntry, stubMode)
         }
 
-        val explicitVisibility = if (primaryConstructor != null) modifiers.getVisibility() else null
+        val explicitVisibility = runIf(primaryConstructor != null) {
+            modifiers.getVisibility().takeUnless { it == Visibilities.Unknown }
+        }
         val status = FirDeclarationStatusImpl(explicitVisibility ?: defaultVisibility, Modality.FINAL).apply {
             isExpect = modifiers.hasExpect() || classWrapper.hasExpect()
             isActual = modifiers.hasActual()

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/fir/ClassWrapper.kt

@@ -64,7 +64,7 @@ class ClassWrapper(
     fun defaultConstructorVisibility(): Visibility {
         return when {
             isObject() || isEnum() || isEnumEntry() -> Visibilities.Private
-            isSealed() -> Visibilities.Private
+            isSealed() -> Visibilities.Protected
             else -> Visibilities.Unknown
         }
     }

compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt

@@ -657,11 +657,11 @@ class RawFirBuilder(
             // See DescriptorUtils#getDefaultConstructorVisibility in core.descriptors
             fun defaultVisibility() = when {
                 owner is KtObjectDeclaration || owner.hasModifier(ENUM_KEYWORD) || owner is KtEnumEntry -> Visibilities.Private
-                owner.hasModifier(SEALED_KEYWORD) -> Visibilities.Private
+                owner.hasModifier(SEALED_KEYWORD) -> Visibilities.Protected
                 else -> Visibilities.Unknown
             }
 
-            val explicitVisibility = this?.visibility
+            val explicitVisibility = this?.visibility?.takeUnless { it == Visibilities.Unknown }
             val status = FirDeclarationStatusImpl(explicitVisibility ?: defaultVisibility(), Modality.FINAL).apply {
                 isExpect = this@toFirConstructor?.hasExpectModifier() == true || owner.hasExpectModifier()
                 isActual = this@toFirConstructor?.hasActualModifier() == true

compiler/fir/raw-fir/psi2fir/testData/rawBuilder/declarations/enums.lazyBodies.txt

@@ -15,7 +15,7 @@ FILE: enums.kt
 
     }
     public? final? enum class Planet : R|kotlin/Enum<Planet>| {
-        public? constructor(m: Double, r: Double): R|Planet| {
+        private constructor(m: Double, r: Double): R|Planet| {
             super<R|kotlin/Enum<Planet>|>()
         }
 
@@ -75,7 +75,7 @@ FILE: enums.kt
 
     }
     public? final? enum class PseudoInsn : R|kotlin/Enum<PseudoInsn>| {
-        public? constructor(signature: String = String(()V)): R|PseudoInsn| {
+        private constructor(signature: String = String(()V)): R|PseudoInsn| {
             super<R|kotlin/Enum<PseudoInsn>|>()
         }
 

compiler/fir/raw-fir/psi2fir/testData/rawBuilder/declarations/enums.txt

@@ -15,7 +15,7 @@ FILE: enums.kt
 
     }
     public? final? enum class Planet : R|kotlin/Enum<Planet>| {
-        public? constructor(m: Double, r: Double): R|Planet| {
+        private constructor(m: Double, r: Double): R|Planet| {
             super<R|kotlin/Enum<Planet>|>()
         }
 
@@ -81,7 +81,7 @@ FILE: enums.kt
 
     }
     public? final? enum class PseudoInsn : R|kotlin/Enum<PseudoInsn>| {
-        public? constructor(signature: String = String(()V)): R|PseudoInsn| {
+        private constructor(signature: String = String(()V)): R|PseudoInsn| {
             super<R|kotlin/Enum<PseudoInsn>|>()
         }
 

compiler/fir/raw-fir/psi2fir/testData/rawBuilder/declarations/enums2.lazyBodies.txt

@@ -14,7 +14,7 @@ FILE: enums2.kt
 
     }
     public? final? enum class SomeEnum : R|kotlin/Enum<SomeEnum>| {
-        public? constructor(x: Some): R|SomeEnum| {
+        private constructor(x: Some): R|SomeEnum| {
             super<R|kotlin/Enum<SomeEnum>|>()
         }
 

compiler/fir/raw-fir/psi2fir/testData/rawBuilder/declarations/enums2.txt

@@ -14,7 +14,7 @@ FILE: enums2.kt
 
     }
     public? final? enum class SomeEnum : R|kotlin/Enum<SomeEnum>| {
-        public? constructor(x: Some): R|SomeEnum| {
+        private constructor(x: Some): R|SomeEnum| {
             super<R|kotlin/Enum<SomeEnum>|>()
         }
 

compiler/testData/asJava/ultraLightClasses/classModifiers.java

@@ -38,7 +38,7 @@ final class TopLevelPrivate /* pkg.TopLevelPrivate*/ {
 }
 
 public abstract class Season /* pkg.Season*/ {
-  private  Season();//  .ctor()
+  protected  Season();//  .ctor()
 
 
   class Nested ...
@@ -53,7 +53,7 @@ public static final class Nested /* pkg.Season.Nested*/ extends pkg.Season {
 public abstract class SealedWithArgs /* pkg.SealedWithArgs*/ {
   private final int a;
 
-  private  SealedWithArgs(int);//  .ctor(int)
+  protected  SealedWithArgs(int);//  .ctor(int)
 
   public final int getA();//  getA()
 

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

@@ -37,4 +37,4 @@ package bar
 
 import foo.Base
 
-class E : <!HIDDEN, SEALED_SUPERTYPE!>Base<!>()
+class E : <!SEALED_SUPERTYPE!>Base<!>()

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

@@ -14,4 +14,4 @@ class A : Base()
 
 package a
 
-class B : <!HIDDEN!>Base<!>()
+class B : Base()

compiler/testData/diagnostics/tests/sealed/kt44861.fir.kt

-// ISSUE: KT-44861
-// DIAGNOSTICS: -UNUSED_VARIABLE
-
-sealed class Foo() {
-    class A : Foo()
-    class B : Foo()
-}
-
-fun Foo(kind: String = "A"): Foo = when (kind) {
-    "A" -> Foo.A()
-    "B" -> Foo.B()
-    else -> throw Exception()
-}
-
-fun main() {
-    val foo = <!SEALED_CLASS_CONSTRUCTOR_CALL!>Foo<!>()
-}

compiler/testData/diagnostics/tests/sealed/kt44861.kt

+// FIR_IDENTICAL
 // ISSUE: KT-44861
 // DIAGNOSTICS: -UNUSED_VARIABLE
 

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

@@ -2,21 +2,21 @@
 // DIAGNOSTICS: -UNUSED_PARAMETER
 
 sealed class Case1(val x: Int) {
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+    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)<!>
+sealed class Case2 protected constructor(val x: Int) {
+    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)<!>
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case3(10) // should OK
     class Inheritor2 : Case3("Hello")
@@ -25,8 +25,8 @@ sealed class Case3 private constructor(val x: Int) {
 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)<!>
+    protected constructor(x: Int)
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case4(10)
     class Inheritor2 : Case4("Hello")
@@ -34,8 +34,8 @@ sealed class Case4 {
 
 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()<!>
+    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.fir.kt

@@ -2,21 +2,21 @@
 // DIAGNOSTICS: -UNUSED_PARAMETER
 
 sealed class Case1(val x: Int) {
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+    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)<!>
+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) {
-    <!NON_PRIVATE_CONSTRUCTOR_IN_SEALED!>protected constructor(s: String) : this(s.length)<!>
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case3(10) // should OK
     class Inheritor2 : Case3("Hello")
@@ -25,8 +25,8 @@ sealed class Case3 private constructor(val x: Int) {
 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)<!>
+    protected constructor(x: Int)
+    protected constructor(s: String) : this(s.length)
 
     class Inheritor1 : Case4(10)
     class Inheritor2 : Case4("Hello")
@@ -34,8 +34,8 @@ sealed class Case4 {
 
 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()<!>
+    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/typealias/typeAliasConstructorWrongClass.fir.kt

@@ -17,8 +17,8 @@ val test3a = <!HIDDEN!>EnumClass<!>()
 
 sealed class SealedClass
 typealias Test4 = SealedClass
-val test4 = <!SEALED_CLASS_CONSTRUCTOR_CALL!>Test4<!>()
-val test4a = <!SEALED_CLASS_CONSTRUCTOR_CALL!>SealedClass<!>()
+val test4 = <!HIDDEN!>Test4<!>()
+val test4a = <!HIDDEN!>SealedClass<!>()
 
 class Outer {
     inner class Inner

compiler/testData/ir/irText/classes/sealedClasses.fir.kt.txt

 sealed class Expr {
-  private constructor() /* primary */ {
+  protected constructor() /* primary */ {
     super/*Any*/()
     /* <init>() */
 

compiler/testData/ir/irText/classes/sealedClasses.fir.txt

 FILE fqName:<root> fileName:/sealedClasses.kt
   CLASS CLASS name:Expr modality:SEALED visibility:public superTypes:[kotlin.Any]
     $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.Expr
-    CONSTRUCTOR visibility:private <> () returnType:<root>.Expr [primary]
+    CONSTRUCTOR visibility:protected <> () returnType:<root>.Expr [primary]
       BLOCK_BODY
         DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Expr modality:SEALED visibility:public superTypes:[kotlin.Any]'
@@ -10,7 +10,7 @@ FILE fqName:<root> fileName:/sealedClasses.kt
       CONSTRUCTOR visibility:public <> (number:kotlin.Double) returnType:<root>.Expr.Const [primary]
         VALUE_PARAMETER name:number index:0 type:kotlin.Double
         BLOCK_BODY
-          DELEGATING_CONSTRUCTOR_CALL 'private constructor <init> () [primary] declared in <root>.Expr'
+          DELEGATING_CONSTRUCTOR_CALL 'protected constructor <init> () [primary] declared in <root>.Expr'
           INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Const modality:FINAL visibility:public superTypes:[<root>.Expr]'
       PROPERTY name:number visibility:public modality:FINAL [val]
         FIELD PROPERTY_BACKING_FIELD name:number type:kotlin.Double visibility:private [final]
@@ -42,7 +42,7 @@ FILE fqName:<root> fileName:/sealedClasses.kt
         VALUE_PARAMETER name:e1 index:0 type:<root>.Expr
         VALUE_PARAMETER name:e2 index:1 type:<root>.Expr
         BLOCK_BODY
-          DELEGATING_CONSTRUCTOR_CALL 'private constructor <init> () [primary] declared in <root>.Expr'
+          DELEGATING_CONSTRUCTOR_CALL 'protected constructor <init> () [primary] declared in <root>.Expr'
           INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Sum modality:FINAL visibility:public superTypes:[<root>.Expr]'
       PROPERTY name:e1 visibility:public modality:FINAL [val]
         FIELD PROPERTY_BACKING_FIELD name:e1 type:<root>.Expr visibility:private [final]
@@ -83,7 +83,7 @@ FILE fqName:<root> fileName:/sealedClasses.kt
       $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.Expr.NotANumber
       CONSTRUCTOR visibility:private <> () returnType:<root>.Expr.NotANumber [primary]
         BLOCK_BODY
-          DELEGATING_CONSTRUCTOR_CALL 'private constructor <init> () [primary] declared in <root>.Expr'
+          DELEGATING_CONSTRUCTOR_CALL 'protected constructor <init> () [primary] declared in <root>.Expr'
           INSTANCE_INITIALIZER_CALL classDescriptor='CLASS OBJECT name:NotANumber modality:FINAL visibility:public superTypes:[<root>.Expr]'
       FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [fake_override,operator]
         overridden:

compiler/testData/ir/irText/declarations/multiplatform/expectedSealedClass.fir.kt.txt

 expect sealed class Ops {
-  private expect constructor() /* primary */
+  protected expect constructor() /* primary */
 
 }
 
@@ -9,7 +9,7 @@ expect class Add : Ops {
 }
 
 sealed class Ops {
-  private constructor() /* primary */ {
+  protected constructor() /* primary */ {
     super/*Any*/()
     /* <init>() */
 

compiler/testData/ir/irText/declarations/multiplatform/expectedSealedClass.fir.txt

 FILE fqName:<root> fileName:/expectedSealedClass.kt
   CLASS CLASS name:Ops modality:SEALED visibility:public [expect] superTypes:[kotlin.Any]
     $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.Ops
-    CONSTRUCTOR visibility:private <> () returnType:<root>.Ops [primary,expect]
+    CONSTRUCTOR visibility:protected <> () returnType:<root>.Ops [primary,expect]
     FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [expect,fake_override,operator]
       overridden:
         public open fun equals (other: kotlin.Any?): kotlin.Boolean [operator] declared in kotlin.Any
@@ -33,7 +33,7 @@ FILE fqName:<root> fileName:/expectedSealedClass.kt
       $this: VALUE_PARAMETER name:<this> type:kotlin.Any
   CLASS CLASS name:Ops modality:SEALED visibility:public superTypes:[kotlin.Any]
     $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.Ops
-    CONSTRUCTOR visibility:private <> () returnType:<root>.Ops [primary]
+    CONSTRUCTOR visibility:protected <> () returnType:<root>.Ops [primary]
       BLOCK_BODY
         DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in kotlin.Any'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Ops modality:SEALED visibility:public superTypes:[kotlin.Any]'
@@ -54,7 +54,7 @@ FILE fqName:<root> fileName:/expectedSealedClass.kt
     $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.Add
     CONSTRUCTOR visibility:public <> () returnType:<root>.Add [primary]
       BLOCK_BODY
-        DELEGATING_CONSTRUCTOR_CALL 'private constructor <init> () [primary] declared in <root>.Ops'
+        DELEGATING_CONSTRUCTOR_CALL 'protected constructor <init> () [primary] declared in <root>.Ops'
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:Add modality:FINAL visibility:public superTypes:[<root>.Ops]'
     FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [fake_override,operator]
       overridden:

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -260,8 +260,8 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
-    add(FirErrors.NON_PRIVATE_CONSTRUCTOR_IN_SEALED) { firDiagnostic ->
-        NonPrivateConstructorInSealedImpl(
+    add(FirErrors.NON_PRIVATE_OR_PROTECTED_CONSTRUCTOR_IN_SEALED) { firDiagnostic ->
+        NonPrivateOrProtectedConstructorInSealedImpl(
             firDiagnostic as FirPsiDiagnostic<*>,
             token,
         )

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -190,8 +190,8 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = NonPrivateConstructorInEnum::class
     }
 
-    abstract class NonPrivateConstructorInSealed : KtFirDiagnostic<PsiElement>() {
-        override val diagnosticClass get() = NonPrivateConstructorInSealed::class
+    abstract class NonPrivateOrProtectedConstructorInSealed : KtFirDiagnostic<PsiElement>() {
+        override val diagnosticClass get() = NonPrivateOrProtectedConstructorInSealed::class
     }
 
     abstract class CyclicConstructorDelegationCall : KtFirDiagnostic<PsiElement>() {

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -299,10 +299,10 @@ internal class NonPrivateConstructorInEnumImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
-internal class NonPrivateConstructorInSealedImpl(
+internal class NonPrivateOrProtectedConstructorInSealedImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
-) : KtFirDiagnostic.NonPrivateConstructorInSealed(), KtAbstractFirDiagnostic<PsiElement> {
+) : KtFirDiagnostic.NonPrivateOrProtectedConstructorInSealed(), KtAbstractFirDiagnostic<PsiElement> {
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }