[FIR] Introduce unused variable extended checker
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/*
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* Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
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* Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
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*/
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package org.jetbrains.kotlin.fir.analysis.checkers.extended
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import kotlinx.collections.immutable.PersistentMap
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import kotlinx.collections.immutable.persistentMapOf
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import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
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import org.jetbrains.kotlin.fir.FirSourceElement
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import org.jetbrains.kotlin.fir.FirSymbolOwner
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import org.jetbrains.kotlin.fir.analysis.cfa.*
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import org.jetbrains.kotlin.fir.analysis.checkers.cfa.FirControlFlowChecker
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import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
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import org.jetbrains.kotlin.fir.analysis.checkers.getContainingClass
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import org.jetbrains.kotlin.fir.analysis.checkers.isIterator
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import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
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import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
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import org.jetbrains.kotlin.fir.analysis.getChildren
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import org.jetbrains.kotlin.fir.expressions.FirFunctionCall
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import org.jetbrains.kotlin.fir.references.FirResolvedNamedReference
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import org.jetbrains.kotlin.fir.resolve.dfa.cfg.*
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import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
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import org.jetbrains.kotlin.lexer.KtTokens
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object UnusedChecker : FirControlFlowChecker() {
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override fun analyze(graph: ControlFlowGraph, reporter: DiagnosticReporter, checkerContext: CheckerContext) {
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if ((graph.declaration as? FirSymbolOwner<*>)?.getContainingClass(checkerContext) != null) return
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val properties = LocalPropertyCollector.collect(graph)
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if (properties.isEmpty()) return
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val data = ValueWritesWithoutReading(properties).getData(graph)
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graph.traverse(TraverseDirection.Backward, CfaVisitor(data, reporter))
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}
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class CfaVisitor(
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val data: Map<CFGNode<*>, VariableStatusInfo>,
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val reporter: DiagnosticReporter
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) : ControlFlowGraphVisitorVoid() {
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override fun visitNode(node: CFGNode<*>) {}
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override fun visitVariableAssignmentNode(node: VariableAssignmentNode) {
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val variableSymbol = (node.fir.calleeReference as? FirResolvedNamedReference)?.resolvedSymbol ?: return
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val data = data[node]?.get(variableSymbol) ?: return
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if (data == VariableStatus.ONLY_WRITTEN_NEVER_READ) {
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// todo: report case like "a += 1" where `a` `doesn't writes` different way (special for Idea)
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val source = node.fir.lValue.source
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reporter.report(source, FirErrors.ASSIGNED_VALUE_IS_NEVER_READ)
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}
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}
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override fun visitVariableDeclarationNode(node: VariableDeclarationNode) {
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val variableSymbol = node.fir.symbol
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if (variableSymbol.isLoopIterator) return
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val data = data[node]?.get(variableSymbol) ?: return
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when {
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data == VariableStatus.UNUSED -> {
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if ((node.fir.initializer as? FirFunctionCall)?.isIterator != true) {
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val source = variableSymbol.identifierSource
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reporter.report(source, FirErrors.UNUSED_VARIABLE)
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}
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}
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data.isRedundantInit -> {
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val source = variableSymbol.fir.initializer?.source
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reporter.report(source, FirErrors.VARIABLE_INITIALIZER_IS_REDUNDANT)
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}
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data == VariableStatus.ONLY_WRITTEN_NEVER_READ -> {
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val source = variableSymbol.identifierSource
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reporter.report(source, FirErrors.VARIABLE_NEVER_READ)
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}
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else -> {
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}
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}
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}
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}
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enum class VariableStatus(private val priority: Int) {
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READ(3),
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WRITTEN_AFTER_READ(2),
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ONLY_WRITTEN_NEVER_READ(1),
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UNUSED(0);
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var isRead = false
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var isRedundantInit = false
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fun merge(variableUseState: VariableStatus?): VariableStatus {
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val base = if (variableUseState == null || priority > variableUseState.priority) this
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else variableUseState
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return base.also {
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it.isRead = this.isRead || variableUseState?.isRead == true
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it.isRedundantInit = this.isRedundantInit && variableUseState?.isRedundantInit == true
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}
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}
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}
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class VariableStatusInfo(
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map: PersistentMap<FirPropertySymbol, VariableStatus> = persistentMapOf()
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) : ControlFlowInfo<VariableStatusInfo, FirPropertySymbol, VariableStatus>(map) {
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companion object {
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val EMPTY = VariableStatusInfo()
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}
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override val constructor: (PersistentMap<FirPropertySymbol, VariableStatus>) -> VariableStatusInfo =
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::VariableStatusInfo
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fun merge(other: VariableStatusInfo): VariableStatusInfo {
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var result = this
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for (symbol in keys.union(other.keys)) {
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val kind1 = this[symbol] ?: VariableStatus.UNUSED
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val kind2 = other[symbol] ?: VariableStatus.UNUSED
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val new = kind1.merge(kind2)
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result = result.put(symbol, new)
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}
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return result
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}
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}
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private class ValueWritesWithoutReading(
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private val localProperties: Set<FirPropertySymbol>
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) : ControlFlowGraphVisitor<VariableStatusInfo, Collection<VariableStatusInfo>>() {
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fun getData(graph: ControlFlowGraph): Map<CFGNode<*>, VariableStatusInfo> {
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println("getting data for local properties set ${localProperties.joinToString()}")
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return graph.collectDataForNode(TraverseDirection.Backward, VariableStatusInfo.EMPTY, this)
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}
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override fun visitNode(node: CFGNode<*>, data: Collection<VariableStatusInfo>): VariableStatusInfo {
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if (data.isEmpty()) return VariableStatusInfo.EMPTY
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return data.reduce(VariableStatusInfo::merge)
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}
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override fun visitVariableDeclarationNode(node: VariableDeclarationNode, data: Collection<VariableStatusInfo>): VariableStatusInfo {
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val dataForNode = visitNode(node, data)
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if (node.fir.source?.kind is FirFakeSourceElementKind) return dataForNode
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val symbol = node.fir.symbol
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return when (dataForNode[symbol]) {
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null -> {
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dataForNode.put(symbol, VariableStatus.UNUSED)
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}
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VariableStatus.ONLY_WRITTEN_NEVER_READ, VariableStatus.WRITTEN_AFTER_READ -> {
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if (node.fir.initializer != null && dataForNode[symbol]?.isRead == true) {
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val newData = dataForNode[symbol] ?: VariableStatus.UNUSED
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newData.isRedundantInit = true
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dataForNode.put(symbol, newData)
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} else if (node.fir.initializer != null) {
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dataForNode.put(symbol, VariableStatus.ONLY_WRITTEN_NEVER_READ)
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} else {
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dataForNode
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}
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}
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VariableStatus.READ -> {
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dataForNode.put(symbol, VariableStatus.READ)
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}
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else -> {
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dataForNode
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}
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}
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}
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override fun visitVariableAssignmentNode(node: VariableAssignmentNode, data: Collection<VariableStatusInfo>): VariableStatusInfo {
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val dataForNode = visitNode(node, data)
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val reference = node.fir.lValue as? FirResolvedNamedReference ?: return dataForNode
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val symbol = reference.resolvedSymbol as? FirPropertySymbol ?: return dataForNode
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val toPut = when {
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symbol !in localProperties -> {
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null
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}
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dataForNode[symbol] == VariableStatus.READ -> {
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VariableStatus.WRITTEN_AFTER_READ
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}
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dataForNode[symbol] == VariableStatus.WRITTEN_AFTER_READ -> {
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VariableStatus.ONLY_WRITTEN_NEVER_READ
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}
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else -> {
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VariableStatus.ONLY_WRITTEN_NEVER_READ.merge(dataForNode[symbol] ?: VariableStatus.UNUSED)
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}
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}
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toPut ?: return dataForNode
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toPut.isRead = dataForNode[symbol]?.isRead ?: false
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return dataForNode.put(symbol, toPut)
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}
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override fun visitQualifiedAccessNode(node: QualifiedAccessNode, data: Collection<VariableStatusInfo>): VariableStatusInfo {
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val dataForNode = visitNode(node, data)
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if (node.fir.source?.kind is FirFakeSourceElementKind) return dataForNode
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val reference = node.fir.calleeReference as? FirResolvedNamedReference ?: return dataForNode
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val symbol = reference.resolvedSymbol as? FirPropertySymbol ?: return dataForNode
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if (symbol !in localProperties) return dataForNode
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val status = VariableStatus.READ
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status.isRead = true
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return dataForNode.put(symbol, status)
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}
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}
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private val FirPropertySymbol.isLoopIterator
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get() = fir.initializer?.source?.kind == FirFakeSourceElementKind.DesugaredForLoop
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private val FirPropertySymbol.identifierSource: FirSourceElement?
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get() = fir.source?.getChildren(KtTokens.IDENTIFIER, 0, 1)
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}
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