FIR-IDE: add mappings for backing field diagnostics

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

@@ -848,6 +848,24 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.BACKING_FIELD_IN_INTERFACE) { firDiagnostic ->
+        BackingFieldInInterfaceImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.EXTENSION_PROPERTY_WITH_BACKING_FIELD) { firDiagnostic ->
+        ExtensionPropertyWithBackingFieldImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.PROPERTY_INITIALIZER_NO_BACKING_FIELD) { firDiagnostic ->
+        PropertyInitializerNoBackingFieldImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.ABSTRACT_DELEGATED_PROPERTY) { firDiagnostic ->
         AbstractDelegatedPropertyImpl(
             firDiagnostic as FirPsiDiagnostic<*>,

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

@@ -602,6 +602,18 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = PropertyWithNoTypeNoInitializer::class
     }
 
+    abstract class BackingFieldInInterface : KtFirDiagnostic<KtProperty>() {
+        override val diagnosticClass get() = BackingFieldInInterface::class
+    }
+
+    abstract class ExtensionPropertyWithBackingField : KtFirDiagnostic<KtExpression>() {
+        override val diagnosticClass get() = ExtensionPropertyWithBackingField::class
+    }
+
+    abstract class PropertyInitializerNoBackingField : KtFirDiagnostic<KtExpression>() {
+        override val diagnosticClass get() = PropertyInitializerNoBackingField::class
+    }
+
     abstract class AbstractDelegatedProperty : KtFirDiagnostic<KtPropertyDelegate>() {
         override val diagnosticClass get() = AbstractDelegatedProperty::class
     }

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

@@ -966,6 +966,27 @@ internal class PropertyWithNoTypeNoInitializerImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class BackingFieldInInterfaceImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.BackingFieldInInterface(), KtAbstractFirDiagnostic<KtProperty> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class ExtensionPropertyWithBackingFieldImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.ExtensionPropertyWithBackingField(), KtAbstractFirDiagnostic<KtExpression> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class PropertyInitializerNoBackingFieldImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.PropertyInitializerNoBackingField(), KtAbstractFirDiagnostic<KtExpression> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class AbstractDelegatedPropertyImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,