FIR checker: report NOT_A_FUNCTION_LABEL

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

@@ -3404,6 +3404,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.NOT_A_FUNCTION_LABEL) { firDiagnostic ->
+        NotAFunctionLabelImpl(
+            firDiagnostic as FirPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.RETURN_IN_FUNCTION_WITH_EXPRESSION_BODY) { firDiagnostic ->
         ReturnInFunctionWithExpressionBodyImpl(
             firDiagnostic as FirPsiDiagnostic,

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

@@ -2371,6 +2371,10 @@ sealed class KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = ReturnNotAllowed::class
     }
 
+    abstract class NotAFunctionLabel : KtFirDiagnostic<KtReturnExpression>() {
+        override val diagnosticClass get() = NotAFunctionLabel::class
+    }
+
     abstract class ReturnInFunctionWithExpressionBody : KtFirDiagnostic<KtReturnExpression>() {
         override val diagnosticClass get() = ReturnInFunctionWithExpressionBody::class
     }

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

@@ -2859,6 +2859,11 @@ internal class ReturnNotAllowedImpl(
     override val token: ValidityToken,
 ) : KtFirDiagnostic.ReturnNotAllowed(), KtAbstractFirDiagnostic<KtReturnExpression>
 
+internal class NotAFunctionLabelImpl(
+    override val firDiagnostic: FirPsiDiagnostic,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.NotAFunctionLabel(), KtAbstractFirDiagnostic<KtReturnExpression>
+
 internal class ReturnInFunctionWithExpressionBodyImpl(
     override val firDiagnostic: FirPsiDiagnostic,
     override val token: ValidityToken,