[FIR] Make default accessors always present

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

@@ -10,6 +10,8 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.declarations.FirProperty
+import org.jetbrains.kotlin.fir.declarations.FirPropertyAccessor
+import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertyAccessor
 import org.jetbrains.kotlin.fir.declarations.utils.hasExplicitBackingField
 import org.jetbrains.kotlin.fir.expressions.FirErrorExpression
 import org.jetbrains.kotlin.fir.typeContext
@@ -45,12 +47,15 @@ object FirPropertyFieldTypeChecker : FirPropertyChecker() {
         }
     }
 
+    private val FirPropertyAccessor?.isNotExplicit
+        get() = this == null || this is FirDefaultPropertyAccessor
+
     private fun checkAsPropertyNotSubtype(
         property: FirProperty,
         context: CheckerContext,
         reporter: DiagnosticReporter
     ) {
-        if (property.isVar && property.setter == null) {
+        if (property.isVar && property.setter.isNotExplicit) {
             reporter.reportOn(property.source, FirErrors.PROPERTY_MUST_HAVE_SETTER, context)
         }
     }
@@ -60,7 +65,7 @@ object FirPropertyFieldTypeChecker : FirPropertyChecker() {
         context: CheckerContext,
         reporter: DiagnosticReporter
     ) {
-        if (property.getter == null) {
+        if (property.getter.isNotExplicit) {
             reporter.reportOn(property.source, FirErrors.PROPERTY_MUST_HAVE_GETTER, context)
         }
     }

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/DeclarationsConverter.kt

@@ -1132,24 +1132,19 @@ class DeclarationsConverter(
                             isExternal = modifiers.hasExternal()
                         }
 
-                    val hasExplicitBackingField = backingField !is FirDefaultPropertyBackingField
                     val convertedAccessors = accessors.map {
-                        convertGetterOrSetter(it, returnType, propertyVisibility, symbol, modifiers, hasExplicitBackingField)
+                        convertGetterOrSetter(it, returnType, propertyVisibility, symbol, modifiers)
                     }
                     this.getter = convertedAccessors.find { it.isGetter }
-                        ?: if (!hasExplicitBackingField) {
-                            FirDefaultPropertyGetter(
-                                property.toFirSourceElement(FirFakeSourceElementKind.DefaultAccessor), moduleData, FirDeclarationOrigin.Source, returnType, propertyVisibility, symbol,
-                            ).also {
-                                it.status = defaultAccessorStatus()
-                                it.initContainingClassAttr()
-                            }
-                        } else {
-                            null
+                        ?: FirDefaultPropertyGetter(
+                            property.toFirSourceElement(FirFakeSourceElementKind.DefaultAccessor), moduleData, FirDeclarationOrigin.Source, returnType, propertyVisibility, symbol,
+                        ).also {
+                            it.status = defaultAccessorStatus()
+                            it.initContainingClassAttr()
                         }
                     // NOTE: We still need the setter even for a val property so we can report errors (e.g., VAL_WITH_SETTER).
                     this.setter = convertedAccessors.find { it.isSetter }
-                        ?: if (isVar && !hasExplicitBackingField) {
+                        ?: if (isVar) {
                             FirDefaultPropertySetter(
                                 property.toFirSourceElement(FirFakeSourceElementKind.DefaultAccessor),
                                 moduleData,
@@ -1259,7 +1254,6 @@ class DeclarationsConverter(
         propertyVisibility: Visibility,
         propertySymbol: FirPropertySymbol,
         propertyModifiers: Modifier,
-        hasBackingField: Boolean,
     ): FirPropertyAccessor {
         var modifiers = Modifier()
         var isGetter = true
@@ -1298,11 +1292,7 @@ class DeclarationsConverter(
                 isExternal = propertyModifiers.hasExternal() || modifiers.hasExternal()
             }
         val sourceElement = getterOrSetter.toFirSourceElement()
-        // If an explicit backing field is present,
-        // the default accessors might not be compatible
-        // with it. We should check the types first, and
-        // only then see if we can create the default accessors.
-        if (block == null && expression == null && !hasBackingField) {
+        if (block == null && expression == null) {
             return FirDefaultPropertyAccessor
                 .createGetterOrSetter(
                     sourceElement,

compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt

@@ -368,7 +368,6 @@ open class RawFirBuilder(
             propertyTypeRef: FirTypeRef,
             propertySymbol: FirPropertySymbol,
             isGetter: Boolean,
-            hasExplicitBackingField: Boolean,
         ): FirPropertyAccessor? {
             val accessorVisibility =
                 if (this?.visibility != null && this.visibility != Visibilities.Unknown) this.visibility else property.visibility
@@ -425,11 +424,7 @@ open class RawFirBuilder(
                         this@RawFirBuilder.context.firFunctionTargets.removeLast()
                     }
                 }
-                // If an explicit backing field is present,
-                // the default accessors might not be compatible
-                // with it. We should check the types first, and
-                // only then see if we can create the default accessors.
-                !hasExplicitBackingField && (isGetter || property.isVar) -> {
+                isGetter || property.isVar -> {
                     // Default getter for val/var properties, and default setter for var properties.
                     val propertySource =
                         this?.toFirSourceElement() ?: property.toFirPsiSourceElement(FirFakeSourceElementKind.DefaultAccessor)
@@ -1531,20 +1526,17 @@ open class RawFirBuilder(
                             propertyType,
                         )
 
-                        val hasExplicitBackingField = backingField !is FirDefaultPropertyBackingField
                         getter = this@toFirProperty.getter.toFirPropertyAccessor(
                             this@toFirProperty,
                             propertyType,
                             propertySymbol = symbol,
-                            isGetter = true,
-                            hasExplicitBackingField,
+                            isGetter = true
                         )
                         setter = this@toFirProperty.setter.toFirPropertyAccessor(
                             this@toFirProperty,
                             propertyType,
                             propertySymbol = symbol,
-                            isGetter = false,
-                            hasExplicitBackingField,
+                            isGetter = false
                         )
 
                         status = FirDeclarationStatusImpl(visibility, modality).apply {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirDeclarationsResolveTransformer.kt

@@ -151,10 +151,6 @@ open class FirDeclarationsResolveTransformer(transformer: FirBodyResolveTransfor
                     }
                     property.transformBackingField(transformer, withExpectedType(property.returnTypeRef))
                 }
-                // In case an explicit backing field declaration
-                // is present, and the default accessors haven't
-                // been generated earlier.
-                property.generateMissingDefaultAccessors()
                 val delegate = property.delegate
                 if (delegate != null) {
                     transformPropertyAccessorsWithDelegate(property, delegate)
@@ -185,50 +181,6 @@ open class FirDeclarationsResolveTransformer(transformer: FirBodyResolveTransfor
         }
     }
 
-    private fun FirProperty.generateMissingDefaultAccessors() {
-        val fieldDeclaration = backingField ?: return
-
-        if (
-            !this.hasExplicitBackingField ||
-            fieldDeclaration.returnTypeRef !is FirResolvedTypeRef
-        ) {
-            return
-        }
-
-        val typeCheckerContext = session.typeContext.newBaseTypeCheckerContext(
-            errorTypesEqualToAnything = false,
-            stubTypesEqualToAnything = false
-        )
-
-        if (getter == null && fieldDeclaration.isSubtypeOf(this, typeCheckerContext)) {
-            this.replaceGetter(
-                FirDefaultPropertyGetter(
-                    null,
-                    this.moduleData,
-                    FirDeclarationOrigin.Source,
-                    this.returnTypeRef,
-                    this.visibility,
-                    this.symbol,
-                ).also {
-                    it.status = this.getDefaultAccessorStatus()
-                }
-            )
-        } else if (this.isVar && this.isSubtypeOf(fieldDeclaration, typeCheckerContext)) {
-            this.replaceSetter(
-                FirDefaultPropertySetter(
-                    null,
-                    this.moduleData,
-                    FirDeclarationOrigin.Source,
-                    this.returnTypeRef,
-                    this.visibility,
-                    this.symbol,
-                ).also {
-                    it.status = this.getDefaultAccessorStatus()
-                }
-            )
-        }
-    }
-
     fun FirProperty.getDefaultAccessorStatus(): FirDeclarationStatus {
         // Downward propagation of `inline` and `external` modifiers (from property to its accessors)
         return FirDeclarationStatusImpl(this.visibility, this.modality).apply {