FIR: introduce FunInterfaceDeclarationChecker

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

@@ -1413,6 +1413,36 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.FUN_INTERFACE_WRONG_COUNT_OF_ABSTRACT_MEMBERS) { firDiagnostic ->
+        FunInterfaceWrongCountOfAbstractMembersImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.FUN_INTERFACE_CANNOT_HAVE_ABSTRACT_PROPERTIES) { firDiagnostic ->
+        FunInterfaceCannotHaveAbstractPropertiesImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.FUN_INTERFACE_ABSTRACT_METHOD_WITH_TYPE_PARAMETERS) { firDiagnostic ->
+        FunInterfaceAbstractMethodWithTypeParametersImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.FUN_INTERFACE_ABSTRACT_METHOD_WITH_DEFAULT_VALUE) { firDiagnostic ->
+        FunInterfaceAbstractMethodWithDefaultValueImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.FUN_INTERFACE_WITH_SUSPEND_FUNCTION) { firDiagnostic ->
+        FunInterfaceWithSuspendFunctionImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.ABSTRACT_PROPERTY_IN_NON_ABSTRACT_CLASS) { firDiagnostic ->
         AbstractPropertyInNonAbstractClassImpl(
             firSymbolBuilder.buildSymbol(firDiagnostic.a as FirDeclaration),

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

@@ -998,6 +998,26 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = FunInterfaceConstructorReference::class
     }
 
+    abstract class FunInterfaceWrongCountOfAbstractMembers : KtFirDiagnostic<KtClass>() {
+        override val diagnosticClass get() = FunInterfaceWrongCountOfAbstractMembers::class
+    }
+
+    abstract class FunInterfaceCannotHaveAbstractProperties : KtFirDiagnostic<KtDeclaration>() {
+        override val diagnosticClass get() = FunInterfaceCannotHaveAbstractProperties::class
+    }
+
+    abstract class FunInterfaceAbstractMethodWithTypeParameters : KtFirDiagnostic<PsiElement>() {
+        override val diagnosticClass get() = FunInterfaceAbstractMethodWithTypeParameters::class
+    }
+
+    abstract class FunInterfaceAbstractMethodWithDefaultValue : KtFirDiagnostic<PsiElement>() {
+        override val diagnosticClass get() = FunInterfaceAbstractMethodWithDefaultValue::class
+    }
+
+    abstract class FunInterfaceWithSuspendFunction : KtFirDiagnostic<KtFunction>() {
+        override val diagnosticClass get() = FunInterfaceWithSuspendFunction::class
+    }
+
     abstract class AbstractPropertyInNonAbstractClass : KtFirDiagnostic<KtModifierListOwner>() {
         override val diagnosticClass get() = AbstractPropertyInNonAbstractClass::class
         abstract val property: KtSymbol

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

@@ -1608,6 +1608,41 @@ internal class FunInterfaceConstructorReferenceImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class FunInterfaceWrongCountOfAbstractMembersImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.FunInterfaceWrongCountOfAbstractMembers(), KtAbstractFirDiagnostic<KtClass> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class FunInterfaceCannotHaveAbstractPropertiesImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.FunInterfaceCannotHaveAbstractProperties(), KtAbstractFirDiagnostic<KtDeclaration> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class FunInterfaceAbstractMethodWithTypeParametersImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.FunInterfaceAbstractMethodWithTypeParameters(), KtAbstractFirDiagnostic<PsiElement> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class FunInterfaceAbstractMethodWithDefaultValueImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.FunInterfaceAbstractMethodWithDefaultValue(), KtAbstractFirDiagnostic<PsiElement> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class FunInterfaceWithSuspendFunctionImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.FunInterfaceWithSuspendFunction(), KtAbstractFirDiagnostic<KtFunction> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class AbstractPropertyInNonAbstractClassImpl(
     override val property: KtSymbol,
     override val containingClass: KtSymbol,