FIR: add getter visibility and setter return type checks

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/RedundantVisibilityModifierChecker.kt

@@ -75,7 +75,7 @@ open class J {
     }
 
     var buf = 0
-        private get() = 42
+        <!GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY!>private<!> get() = 42
         protected set(value) {
             field = value
         }

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -547,6 +547,8 @@ object DIAGNOSTICS_LIST : DiagnosticList() {
             parameter<ConeKotlinType>("expected")
             parameter<ConeKotlinType>("actual")
         }
+        val GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY by error<KtModifierListOwner>(PositioningStrategy.VISIBILITY_MODIFIER)
+        val WRONG_SETTER_RETURN_TYPE by error<KtProperty>()
     }
 
     val MPP_PROJECTS by object : DiagnosticGroup("Multi-platform projects") {

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -338,6 +338,8 @@ object FirErrors {
     val CONST_VAL_WITH_NON_CONST_INITIALIZER by error0<KtExpression>()
     val WRONG_SETTER_PARAMETER_TYPE by error2<KtTypeReference, ConeKotlinType, ConeKotlinType>()
     val INITIALIZER_TYPE_MISMATCH by error2<KtProperty, ConeKotlinType, ConeKotlinType>(SourceElementPositioningStrategies.ASSIGNMENT_VALUE)
+    val GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY by error0<KtModifierListOwner>(SourceElementPositioningStrategies.VISIBILITY_MODIFIER)
+    val WRONG_SETTER_RETURN_TYPE by error0<KtProperty>()
 
     // Multi-platform projects
     val EXPECTED_DECLARATION_WITH_BODY by error0<KtDeclaration>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirPropertyAccessorChecker.kt

@@ -11,14 +11,26 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.analysis.diagnostics.withSuppressedDiagnostics
 import org.jetbrains.kotlin.fir.declarations.FirProperty
+import org.jetbrains.kotlin.fir.declarations.visibility
 import org.jetbrains.kotlin.fir.types.ConeClassErrorType
 import org.jetbrains.kotlin.fir.types.coneType
+import org.jetbrains.kotlin.fir.types.isUnit
 
 object FirPropertyAccessorChecker : FirPropertyChecker() {
     override fun check(declaration: FirProperty, context: CheckerContext, reporter: DiagnosticReporter) {
+        checkGetter(declaration, context, reporter)
         checkSetter(declaration, context, reporter)
     }
 
+    private fun checkGetter(property: FirProperty, context: CheckerContext, reporter: DiagnosticReporter) {
+        val getter = property.getter ?: return
+        withSuppressedDiagnostics(getter, context) {
+            if (getter.visibility != property.visibility) {
+                reporter.reportOn(getter.source, FirErrors.GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY, context)
+            }
+        }
+    }
+
     private fun checkSetter(property: FirProperty, context: CheckerContext, reporter: DiagnosticReporter) {
         val setter = property.setter ?: return
 
@@ -43,6 +55,15 @@ object FirPropertyAccessorChecker : FirPropertyChecker() {
                     reporter.reportOn(valueSetterTypeSource, FirErrors.WRONG_SETTER_PARAMETER_TYPE, propertyType, valueSetterType, context)
                 }
             }
+
+            val setterReturnType = setter.returnTypeRef.coneType
+            if (propertyType is ConeClassErrorType || valueSetterType is ConeClassErrorType) {
+                return
+            }
+
+            if (!setterReturnType.isUnit) {
+                reporter.reportOn(setter.returnTypeRef.source, FirErrors.WRONG_SETTER_RETURN_TYPE, context)
+            }
         }
     }
 }

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/checkers/CommonDeclarationCheckers.kt

@@ -28,8 +28,8 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
             FirExposedVisibilityDeclarationChecker,
             FirSealedSupertypeChecker,
             FirTypeAliasChecker,
-        FirCyclicTypeBoundsChecker,
+            FirCyclicTypeBoundsChecker,
-    )
+        )
 
     override val functionCheckers: Set<FirFunctionChecker>
         get() = setOf(
@@ -40,8 +40,8 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
     override val simpleFunctionCheckers: Set<FirSimpleFunctionChecker>
         get() = setOf(
             FirFunctionNameChecker,
-        FirFunctionTypeParametersChecker,
+            FirFunctionTypeParametersChecker,
-    )
+        )
 
     override val propertyCheckers: Set<FirPropertyChecker>
         get() = setOf(
@@ -110,7 +110,7 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
     override val typeParameterCheckers: Set<FirTypeParameterChecker>
         get() = setOf(
             FirTypeParameterBoundsChecker,
-        FirTypeParameterVarianceChecker,
+            FirTypeParameterVarianceChecker,
-        FirReifiedTypeParameterChecker,
+            FirReifiedTypeParameterChecker,
-    )
+        )
 }

compiler/testData/diagnostics/tests/AbstractAccessor.fir.kt

@@ -4,14 +4,14 @@ abstract class My {
         <!PRIVATE_SETTER_FOR_ABSTRACT_PROPERTY!>private<!> set
 
     abstract val y: Int
-        protected get
+        <!GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY!>protected<!> get
 
     abstract protected var z: Int
-        internal get
+        <!GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY!>internal<!> get
         <!PRIVATE_SETTER_FOR_ABSTRACT_PROPERTY!>private<!> set
 
     abstract internal val w: Int
-        protected get
+        <!GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY!>protected<!> get
 
     abstract var u: Int
         protected set

compiler/testData/diagnostics/tests/backingField/SetterWithExplicitType.fir.kt

@@ -1,26 +0,0 @@
-// KT-7042 Providing return type for property setter is not reported as error
-
-var x: Int = 1
-
-// No backing field!
-var y: Int
-    get() = x
-    set(value): Any {
-        x = value
-    }
-
-var z: Int
-    get() = x
-    set(value): Unit {
-        x = value
-    }
-
-var u: String = ""
-    set(value): Unit {
-        field = value
-    }
-
-var v: String = ""
-    set(value): String {
-        field = value
-    }

compiler/testData/diagnostics/tests/backingField/SetterWithExplicitType.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // KT-7042 Providing return type for property setter is not reported as error
 
 var x: Int = 1

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

@@ -1581,6 +1581,18 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.GETTER_VISIBILITY_DIFFERS_FROM_PROPERTY_VISIBILITY) { firDiagnostic ->
+        GetterVisibilityDiffersFromPropertyVisibilityImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.WRONG_SETTER_RETURN_TYPE) { firDiagnostic ->
+        WrongSetterReturnTypeImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.EXPECTED_DECLARATION_WITH_BODY) { firDiagnostic ->
         ExpectedDeclarationWithBodyImpl(
             firDiagnostic as FirPsiDiagnostic<*>,

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

@@ -1112,6 +1112,14 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         abstract val actual: KtType
     }
 
+    abstract class GetterVisibilityDiffersFromPropertyVisibility : KtFirDiagnostic<KtModifierListOwner>() {
+        override val diagnosticClass get() = GetterVisibilityDiffersFromPropertyVisibility::class
+    }
+
+    abstract class WrongSetterReturnType : KtFirDiagnostic<KtProperty>() {
+        override val diagnosticClass get() = WrongSetterReturnType::class
+    }
+
     abstract class ExpectedDeclarationWithBody : KtFirDiagnostic<KtDeclaration>() {
         override val diagnosticClass get() = ExpectedDeclarationWithBody::class
     }

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

@@ -1803,6 +1803,20 @@ internal class InitializerTypeMismatchImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class GetterVisibilityDiffersFromPropertyVisibilityImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.GetterVisibilityDiffersFromPropertyVisibility(), KtAbstractFirDiagnostic<KtModifierListOwner> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class WrongSetterReturnTypeImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.WrongSetterReturnType(), KtAbstractFirDiagnostic<KtProperty> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class ExpectedDeclarationWithBodyImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,