Add applicability checks & tests for SubclassOptInRequired

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

@@ -1041,6 +1041,13 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.SUBCLASS_OPT_IN_INAPPLICABLE) { firDiagnostic ->
+        SubclassOptInInapplicableImpl(
+            firDiagnostic.a,
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.EXPOSED_TYPEALIAS_EXPANDED_TYPE) { firDiagnostic ->
         ExposedTypealiasExpandedTypeImpl(
             firDiagnostic.a,

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

@@ -751,6 +751,11 @@ sealed class KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = OptInMarkerOnOverrideWarning::class
     }
 
+    abstract class SubclassOptInInapplicable : KtFirDiagnostic<KtAnnotationEntry>() {
+        override val diagnosticClass get() = SubclassOptInInapplicable::class
+        abstract val target: String
+    }
+
     abstract class ExposedTypealiasExpandedType : KtFirDiagnostic<KtNamedDeclaration>() {
         override val diagnosticClass get() = ExposedTypealiasExpandedType::class
         abstract val elementVisibility: EffectiveVisibility

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

@@ -902,6 +902,12 @@ internal class OptInMarkerOnOverrideWarningImpl(
     override val token: KtLifetimeToken,
 ) : KtFirDiagnostic.OptInMarkerOnOverrideWarning(), KtAbstractFirDiagnostic<KtAnnotationEntry>
 
+internal class SubclassOptInInapplicableImpl(
+    override val target: String,
+    override val firDiagnostic: KtPsiDiagnostic,
+    override val token: KtLifetimeToken,
+) : KtFirDiagnostic.SubclassOptInInapplicable(), KtAbstractFirDiagnostic<KtAnnotationEntry>
+
 internal class ExposedTypealiasExpandedTypeImpl(
     override val elementVisibility: EffectiveVisibility,
     override val restrictingDeclaration: KtSymbol,

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -37548,6 +37548,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/testsWithStdLib/experimental/overrideInAnonymousObject.kt");
             }
 
+            @Test
+            @TestMetadata("subClassOptInModality.kt")
+            public void testSubClassOptInModality() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/experimental/subClassOptInModality.kt");
+            }
+
             @Test
             @TestMetadata("subClassOptInRequired.kt")
             public void testSubClassOptInRequired() throws Exception {