[FIR] Implement CONFLICTING_INHERITED_MEMBERS diagnostic

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

@@ -1700,6 +1700,15 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.CONFLICTING_INHERITED_MEMBERS) { firDiagnostic ->
+        ConflictingInheritedMembersImpl(
+            firDiagnostic.a.map { firCallableDeclaration ->
+                firSymbolBuilder.callableBuilder.buildCallableSymbol(firCallableDeclaration as FirCallableDeclaration)
+            },
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.ABSTRACT_MEMBER_NOT_IMPLEMENTED) { firDiagnostic ->
         AbstractMemberNotImplementedImpl(
             firSymbolBuilder.classifierBuilder.buildClassLikeSymbol(firDiagnostic.a),

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

@@ -1207,6 +1207,11 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         abstract val baseDeclaration: KtCallableSymbol
     }
 
+    abstract class ConflictingInheritedMembers : KtFirDiagnostic<KtClassOrObject>() {
+        override val diagnosticClass get() = ConflictingInheritedMembers::class
+        abstract val conflictingDeclarations: List<KtCallableSymbol>
+    }
+
     abstract class AbstractMemberNotImplemented : KtFirDiagnostic<KtClassOrObject>() {
         override val diagnosticClass get() = AbstractMemberNotImplemented::class
         abstract val classOrObject: KtClassLikeSymbol

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

@@ -1937,6 +1937,14 @@ internal class VarOverriddenByValByDelegationImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class ConflictingInheritedMembersImpl(
+    override val conflictingDeclarations: List<KtCallableSymbol>,
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.ConflictingInheritedMembers(), KtAbstractFirDiagnostic<KtClassOrObject> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class AbstractMemberNotImplementedImpl(
     override val classOrObject: KtClassLikeSymbol,
     override val missingDeclaration: KtCallableSymbol,