[FIR] Quick fix FirModifierChecker

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

@@ -877,12 +877,6 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
         val PROPERTY_FIELD_DECLARATION_MISSING_INITIALIZER by error<KtBackingField>()
         val PROPERTY_MUST_HAVE_GETTER by error<KtProperty>()
         val PROPERTY_MUST_HAVE_SETTER by error<KtProperty>()
-        val INAPPLICABLE_BACKING_FIELD_VISIBILITY by error<PsiElement> {
-            parameter<KtModifierKeywordToken>("modifier")
-        }
-        val INAPPLICABLE_BACKING_FIELD_MODIFIER by error<PsiElement> {
-            parameter<KtModifierKeywordToken>("modifier")
-        }
         val EXPLICIT_BACKING_FIELD_IN_INTERFACE by error<KtBackingField>()
         val EXPLICIT_BACKING_FIELD_IN_ABSTRACT_PROPERTY by error<KtBackingField>()
         val ABSTRACT_PROPERTY_IN_PRIMARY_CONSTRUCTOR_PARAMETERS by error<KtModifierListOwner>(PositioningStrategy.ABSTRACT_MODIFIER)

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

@@ -484,8 +484,6 @@ object FirErrors {
     val PROPERTY_FIELD_DECLARATION_MISSING_INITIALIZER by error0<KtBackingField>()
     val PROPERTY_MUST_HAVE_GETTER by error0<KtProperty>()
     val PROPERTY_MUST_HAVE_SETTER by error0<KtProperty>()
-    val INAPPLICABLE_BACKING_FIELD_VISIBILITY by error1<PsiElement, KtModifierKeywordToken>()
-    val INAPPLICABLE_BACKING_FIELD_MODIFIER by error1<PsiElement, KtModifierKeywordToken>()
     val EXPLICIT_BACKING_FIELD_IN_INTERFACE by error0<KtBackingField>()
     val EXPLICIT_BACKING_FIELD_IN_ABSTRACT_PROPERTY by error0<KtBackingField>()
     val ABSTRACT_PROPERTY_IN_PRIMARY_CONSTRUCTOR_PARAMETERS by error0<KtModifierListOwner>(SourceElementPositioningStrategies.ABSTRACT_MODIFIER)

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

@@ -62,7 +62,6 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
 
     override val backingFieldCheckers: Set<FirBackingFieldChecker>
         get() = setOf(
-            FirBackingFieldModifiersChecker,
             FirExplicitBackingFieldInInterfaceChecker,
         )
 

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt

@@ -742,6 +742,7 @@ fun getActualTargetList(annotated: FirDeclaration): AnnotationTargetList {
         }
         is FirTypeAlias -> TargetLists.T_TYPEALIAS
         is FirPropertyAccessor -> if (annotated.isGetter) TargetLists.T_PROPERTY_GETTER else TargetLists.T_PROPERTY_SETTER
+        is FirBackingField -> TargetLists.T_BACKING_FIELD
         is FirFile -> TargetLists.T_FILE
         is FirTypeParameter -> TargetLists.T_TYPE_PARAMETER
         is FirAnonymousInitializer -> TargetLists.T_INITIALIZER

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

@@ -1,46 +0,0 @@
-/*
- * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.fir.analysis.checkers.declaration
-
-import org.jetbrains.kotlin.fir.analysis.checkers.FirModifier
-import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
-import org.jetbrains.kotlin.fir.analysis.checkers.getModifierList
-import org.jetbrains.kotlin.fir.analysis.checkers.toVisibilityOrNull
-import org.jetbrains.kotlin.fir.analysis.diagnostics.*
-import org.jetbrains.kotlin.fir.declarations.FirBackingField
-import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
-import org.jetbrains.kotlin.lexer.KtTokens
-
-object FirBackingFieldModifiersChecker : FirBackingFieldChecker() {
-    private val ALLOWED_MODIFIERS = setOf(
-        KtTokens.PRIVATE_KEYWORD,
-        KtTokens.INTERNAL_KEYWORD,
-    )
-
-    override fun check(declaration: FirBackingField, context: CheckerContext, reporter: DiagnosticReporter) {
-        val modifiers = declaration.source
-            ?.getModifierList()
-            ?.modifiers
-            ?: return
-
-        modifiers.forEach {
-            if (it.token in ALLOWED_MODIFIERS) {
-                return@forEach
-            }
-
-            val diagnostic = reportInapplicable(it)
-            reporter.reportOn(it.source, diagnostic, it.token, context)
-        }
-    }
-
-    private fun reportInapplicable(modifier: FirModifier<*>): FirDiagnosticFactory1<KtModifierKeywordToken> {
-        return if (modifier.token.toVisibilityOrNull() != null) {
-            FirErrors.INAPPLICABLE_BACKING_FIELD_VISIBILITY
-        } else {
-            FirErrors.INAPPLICABLE_BACKING_FIELD_MODIFIER
-        }
-    }
-}

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt

@@ -270,8 +270,6 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MANY_LAMBDA_EXPRE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.METHOD_OF_ANY_IMPLEMENTED_IN_INTERFACE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MISPLACED_TYPE_PARAMETER_CONSTRAINTS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MISSING_VAL_ON_ANNOTATION_PARAMETER
-import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INAPPLICABLE_BACKING_FIELD_MODIFIER
-import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INAPPLICABLE_BACKING_FIELD_VISIBILITY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MODIFIER_FORM_FOR_NON_BUILT_IN_SUSPEND
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MULTIPLE_VARARG_PARAMETERS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MUST_BE_INITIALIZED
@@ -1291,16 +1289,6 @@ class FirDefaultErrorMessages {
                 PROPERTY_MUST_HAVE_SETTER,
                 "This property needs a custom setter, because it's type is not a subtype of the backing field's type"
             )
-            map.put(
-                INAPPLICABLE_BACKING_FIELD_VISIBILITY,
-                "Explicit backing field declarations may only be private or internal, but not ''{0}''",
-                TO_STRING
-            )
-            map.put(
-                INAPPLICABLE_BACKING_FIELD_MODIFIER,
-                "Modifier ''{0}'' is not applicable to explicit backing field declarations",
-                TO_STRING
-            )
             map.put(
                 EXPLICIT_BACKING_FIELD_IN_INTERFACE,
                 "Backing fields are not allowed inside interfaces"

compiler/psi/src/org/jetbrains/kotlin/resolve/ModifierCheckerHelpers.kt

@@ -147,7 +147,7 @@ val featureDependenciesTargets = mapOf(
 val defaultVisibilityTargets: EnumSet<KotlinTarget> = EnumSet.of(
     KotlinTarget.CLASS_ONLY, KotlinTarget.OBJECT, KotlinTarget.INTERFACE, KotlinTarget.ENUM_CLASS, KotlinTarget.ANNOTATION_CLASS,
     KotlinTarget.MEMBER_FUNCTION, KotlinTarget.TOP_LEVEL_FUNCTION, KotlinTarget.PROPERTY_GETTER, KotlinTarget.PROPERTY_SETTER,
-    KotlinTarget.MEMBER_PROPERTY, KotlinTarget.TOP_LEVEL_PROPERTY, KotlinTarget.CONSTRUCTOR, KotlinTarget.TYPEALIAS
+    KotlinTarget.MEMBER_PROPERTY, KotlinTarget.TOP_LEVEL_PROPERTY, KotlinTarget.CONSTRUCTOR, KotlinTarget.TYPEALIAS,
 )
 
 val possibleTargetMap = mapOf(
@@ -177,9 +177,9 @@ val possibleTargetMap = mapOf(
     SEALED_KEYWORD to EnumSet.of(KotlinTarget.CLASS_ONLY, KotlinTarget.INTERFACE),
     INNER_KEYWORD to EnumSet.of(KotlinTarget.CLASS_ONLY),
     OVERRIDE_KEYWORD to EnumSet.of(KotlinTarget.MEMBER_PROPERTY, KotlinTarget.MEMBER_FUNCTION),
-    PRIVATE_KEYWORD to defaultVisibilityTargets,
+    PRIVATE_KEYWORD to defaultVisibilityTargets + KotlinTarget.BACKING_FIELD,
     PUBLIC_KEYWORD to defaultVisibilityTargets,
-    INTERNAL_KEYWORD to defaultVisibilityTargets,
+    INTERNAL_KEYWORD to defaultVisibilityTargets + KotlinTarget.BACKING_FIELD,
     PROTECTED_KEYWORD to EnumSet.of(
         KotlinTarget.CLASS_ONLY,
         KotlinTarget.OBJECT,

core/compiler.common/src/org/jetbrains/kotlin/descriptors/annotations/KotlinTarget.kt

@@ -56,6 +56,8 @@ enum class KotlinTarget(val description: String, val isDefault: Boolean = true)
     TOP_LEVEL_PROPERTY_WITH_DELEGATE("top level property with delegate", false),
     TOP_LEVEL_PROPERTY_WITHOUT_FIELD_OR_DELEGATE("top level property without backing field or delegate", false),
 
+    BACKING_FIELD("backing field"),
+
     INITIALIZER("initializer", false),
     DESTRUCTURING_DECLARATION("destructuring declaration", false),
     LAMBDA_EXPRESSION("lambda expression", false),

core/compiler.common/src/org/jetbrains/kotlin/resolve/AnnotationTargetLists.kt

@@ -54,6 +54,7 @@ object AnnotationTargetLists {
 
     val T_PROPERTY_GETTER = targetList(PROPERTY_GETTER)
     val T_PROPERTY_SETTER = targetList(PROPERTY_SETTER)
+    val T_BACKING_FIELD = targetList(BACKING_FIELD)
 
     val T_VALUE_PARAMETER_WITHOUT_VAL = targetList(VALUE_PARAMETER)
 

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

@@ -2430,20 +2430,6 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
-    add(FirErrors.INAPPLICABLE_BACKING_FIELD_VISIBILITY) { firDiagnostic ->
-        InapplicableBackingFieldVisibilityImpl(
-            firDiagnostic.a,
-            firDiagnostic as FirPsiDiagnostic,
-            token,
-        )
-    }
-    add(FirErrors.INAPPLICABLE_BACKING_FIELD_MODIFIER) { firDiagnostic ->
-        InapplicableBackingFieldModifierImpl(
-            firDiagnostic.a,
-            firDiagnostic as FirPsiDiagnostic,
-            token,
-        )
-    }
     add(FirErrors.EXPLICIT_BACKING_FIELD_IN_INTERFACE) { firDiagnostic ->
         ExplicitBackingFieldInInterfaceImpl(
             firDiagnostic as FirPsiDiagnostic,

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

@@ -1719,16 +1719,6 @@ sealed class KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = PropertyMustHaveSetter::class
     }
 
-    abstract class InapplicableBackingFieldVisibility : KtFirDiagnostic<PsiElement>() {
-        override val diagnosticClass get() = InapplicableBackingFieldVisibility::class
-        abstract val modifier: KtModifierKeywordToken
-    }
-
-    abstract class InapplicableBackingFieldModifier : KtFirDiagnostic<PsiElement>() {
-        override val diagnosticClass get() = InapplicableBackingFieldModifier::class
-        abstract val modifier: KtModifierKeywordToken
-    }
-
     abstract class ExplicitBackingFieldInInterface : KtFirDiagnostic<KtBackingField>() {
         override val diagnosticClass get() = ExplicitBackingFieldInInterface::class
     }

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

@@ -2818,6 +2818,13 @@ internal class ExplicitBackingFieldInAbstractPropertyImpl(
     override val firDiagnostic: FirPsiDiagnostic by weakRef(firDiagnostic)
 }
 
+internal class AbstractPropertyInPrimaryConstructorParametersImpl(
+    firDiagnostic: FirPsiDiagnostic,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.AbstractPropertyInPrimaryConstructorParameters(), KtAbstractFirDiagnostic<KtModifierListOwner> {
+    override val firDiagnostic: FirPsiDiagnostic by weakRef(firDiagnostic)
+}
+
 internal class ExpectedDeclarationWithBodyImpl(
     firDiagnostic: FirPsiDiagnostic,
     override val token: ValidityToken,