[FIR] Forbid multiple labels per statement

^KT-53629: Fixed

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

@@ -4957,6 +4957,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.MULTIPLE_LABELS_ARE_FORBIDDEN) { firDiagnostic ->
+        MultipleLabelsAreForbiddenImpl(
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.DEPRECATED_ACCESS_TO_ENUM_ENTRY_COMPANION_PROPERTY) { firDiagnostic ->
         DeprecatedAccessToEnumEntryCompanionPropertyImpl(
             firDiagnostic as KtPsiDiagnostic,

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

@@ -3450,6 +3450,10 @@ sealed interface KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = RedundantLabelWarning::class
     }
 
+    interface MultipleLabelsAreForbidden : KtFirDiagnostic<KtLabelReferenceExpression> {
+        override val diagnosticClass get() = MultipleLabelsAreForbidden::class
+    }
+
     interface DeprecatedAccessToEnumEntryCompanionProperty : KtFirDiagnostic<PsiElement> {
         override val diagnosticClass get() = DeprecatedAccessToEnumEntryCompanionProperty::class
     }

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

@@ -4161,6 +4161,11 @@ internal class RedundantLabelWarningImpl(
     token: KtLifetimeToken,
 ) : KtAbstractFirDiagnostic<KtLabelReferenceExpression>(firDiagnostic, token), KtFirDiagnostic.RedundantLabelWarning
 
+internal class MultipleLabelsAreForbiddenImpl(
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<KtLabelReferenceExpression>(firDiagnostic, token), KtFirDiagnostic.MultipleLabelsAreForbidden
+
 internal class DeprecatedAccessToEnumEntryCompanionPropertyImpl(
     firDiagnostic: KtPsiDiagnostic,
     token: KtLifetimeToken,

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -23901,6 +23901,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
             public void testLabelsMustBeNamed() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/labels/labelsMustBeNamed.kt");
             }
+
+            @Test
+            @TestMetadata("multipleLabels.kt")
+            public void testMultipleLabels() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/labels/multipleLabels.kt");
+            }
         }
 
         @Nested

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -23901,6 +23901,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
             public void testLabelsMustBeNamed() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/labels/labelsMustBeNamed.kt");
             }
+
+            @Test
+            @TestMetadata("multipleLabels.kt")
+            public void testMultipleLabels() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/labels/multipleLabels.kt");
+            }
         }
 
         @Nested