[FIR] Report UNSUPPORTED_SEALED_FUN_INTERFACE

^KT-59957 Fixed

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

@@ -650,6 +650,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.UNSUPPORTED_SEALED_FUN_INTERFACE) { firDiagnostic ->
+        UnsupportedSealedFunInterfaceImpl(
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.SUPERTYPE_NOT_A_CLASS_OR_INTERFACE) { firDiagnostic ->
         SupertypeNotAClassOrInterfaceImpl(
             firDiagnostic.a,

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

@@ -497,6 +497,10 @@ sealed interface KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = ClassInheritsJavaSealedClass::class
     }
 
+    interface UnsupportedSealedFunInterface : KtFirDiagnostic<PsiElement> {
+        override val diagnosticClass get() = UnsupportedSealedFunInterface::class
+    }
+
     interface SupertypeNotAClassOrInterface : KtFirDiagnostic<KtElement> {
         override val diagnosticClass get() = SupertypeNotAClassOrInterface::class
         val reason: String

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

@@ -584,6 +584,11 @@ internal class ClassInheritsJavaSealedClassImpl(
     token: KtLifetimeToken,
 ) : KtAbstractFirDiagnostic<KtTypeReference>(firDiagnostic, token), KtFirDiagnostic.ClassInheritsJavaSealedClass
 
+internal class UnsupportedSealedFunInterfaceImpl(
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<PsiElement>(firDiagnostic, token), KtFirDiagnostic.UnsupportedSealedFunInterface
+
 internal class SupertypeNotAClassOrInterfaceImpl(
     override val reason: String,
     firDiagnostic: KtPsiDiagnostic,

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

@@ -245,6 +245,7 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
         val SEALED_INHERITOR_IN_DIFFERENT_PACKAGE by error<KtTypeReference>()
         val SEALED_INHERITOR_IN_DIFFERENT_MODULE by error<KtTypeReference>()
         val CLASS_INHERITS_JAVA_SEALED_CLASS by error<KtTypeReference>()
+        val UNSUPPORTED_SEALED_FUN_INTERFACE by error<PsiElement>()
         val SUPERTYPE_NOT_A_CLASS_OR_INTERFACE by error<KtElement> {
             parameter<String>("reason")
         }

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

@@ -213,6 +213,7 @@ object FirErrors {
     val SEALED_INHERITOR_IN_DIFFERENT_PACKAGE by error0<KtTypeReference>()
     val SEALED_INHERITOR_IN_DIFFERENT_MODULE by error0<KtTypeReference>()
     val CLASS_INHERITS_JAVA_SEALED_CLASS by error0<KtTypeReference>()
+    val UNSUPPORTED_SEALED_FUN_INTERFACE by error0<PsiElement>()
     val SUPERTYPE_NOT_A_CLASS_OR_INTERFACE by error1<KtElement, String>()
     val UNSUPPORTED_INHERITANCE_FROM_JAVA_MEMBER_REFERENCING_KOTLIN_FUNCTION by error1<PsiElement, FirBasedSymbol<*>>(SourceElementPositioningStrategies.DECLARATION_NAME)
     val CYCLIC_INHERITANCE_HIERARCHY by error0<PsiElement>()

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonDeclarationCheckers.kt

@@ -106,6 +106,7 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
             FirDynamicSupertypeChecker,
             FirEnumCompanionInEnumConstructorCallChecker,
             FirBadInheritedJavaSignaturesChecker,
+            FirSealedInterfaceAllowedChecker,
         )
 
     override val regularClassCheckers: Set<FirRegularClassChecker>

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

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2010-2023 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.fir.analysis.checkers.declaration
+
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.getModifier
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.declarations.FirClass
+import org.jetbrains.kotlin.fir.declarations.utils.isFun
+import org.jetbrains.kotlin.fir.declarations.utils.isInterface
+import org.jetbrains.kotlin.lexer.KtTokens
+
+object FirSealedInterfaceAllowedChecker : FirClassChecker() {
+    override fun check(declaration: FirClass, context: CheckerContext, reporter: DiagnosticReporter) {
+        if (!declaration.isInterface || !declaration.isFun) {
+            return
+        }
+        val keyword = declaration.getModifier(KtTokens.SEALED_KEYWORD) ?: return
+        reporter.reportOn(keyword.source, FirErrors.UNSUPPORTED_SEALED_FUN_INTERFACE, context)
+    }
+}

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

@@ -121,6 +121,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CAST_NEVER_SUCCEE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CATCH_PARAMETER_WITH_DEFAULT_VALUE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CLASS_CANNOT_BE_EXTENDED_DIRECTLY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CLASS_INHERITS_JAVA_SEALED_CLASS
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNSUPPORTED_SEALED_FUN_INTERFACE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CLASS_IN_SUPERTYPE_FOR_ENUM
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.CLASS_LITERAL_LHS_NOT_A_CLASS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.COMMA_IN_WHEN_CONDITION_WITHOUT_ARGUMENT
@@ -819,6 +820,7 @@ object FirErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
         )
         map.put(SEALED_INHERITOR_IN_DIFFERENT_MODULE, "Inheritance of sealed classes or interfaces from different module is prohibited")
         map.put(CLASS_INHERITS_JAVA_SEALED_CLASS, "Inheritance of Java sealed classes is prohibited")
+        map.put(UNSUPPORTED_SEALED_FUN_INTERFACE, "'sealed fun interface' is unsupported")
 
         map.put(SUPERTYPE_NOT_A_CLASS_OR_INTERFACE, "Supertype is not a class or interface", TO_STRING)
         map.put(

compiler/testData/diagnostics/tests/sealed/interfaces/sealedFunInterface.fir.kt

@@ -1,15 +0,0 @@
-sealed fun interface A { // error
-    fun foo()
-}
-
-sealed interface Base {
-    sealed fun interface Derived : Base {  // error
-        fun foo()
-    }
-}
-
-sealed interface IBase {
-    fun interface IDerived : IBase { // OK
-        fun foo()
-    }
-}

compiler/testData/diagnostics/tests/sealed/interfaces/sealedFunInterface.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 <!UNSUPPORTED_SEALED_FUN_INTERFACE!>sealed<!> fun interface A { // error
     fun foo()
 }