284 lines
9.5 KiB
JavaScript
284 lines
9.5 KiB
JavaScript
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/**
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* @fileoverview disallow assignments that can lead to race conditions due to usage of `await` or `yield`
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* @author Teddy Katz
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* @author Toru Nagashima
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*/
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"use strict";
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/**
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* Make the map from identifiers to each reference.
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* @param {escope.Scope} scope The scope to get references.
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* @param {Map<Identifier, escope.Reference>} [outReferenceMap] The map from identifier nodes to each reference object.
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* @returns {Map<Identifier, escope.Reference>} `referenceMap`.
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*/
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function createReferenceMap(scope, outReferenceMap = new Map()) {
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for (const reference of scope.references) {
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outReferenceMap.set(reference.identifier, reference);
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}
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for (const childScope of scope.childScopes) {
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if (childScope.type !== "function") {
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createReferenceMap(childScope, outReferenceMap);
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}
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}
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return outReferenceMap;
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}
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/**
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* Get `reference.writeExpr` of a given reference.
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* If it's the read reference of MemberExpression in LHS, returns RHS in order to address `a.b = await a`
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* @param {escope.Reference} reference The reference to get.
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* @returns {Expression|null} The `reference.writeExpr`.
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*/
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function getWriteExpr(reference) {
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if (reference.writeExpr) {
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return reference.writeExpr;
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}
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let node = reference.identifier;
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while (node) {
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const t = node.parent.type;
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if (t === "AssignmentExpression" && node.parent.left === node) {
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return node.parent.right;
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}
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if (t === "MemberExpression" && node.parent.object === node) {
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node = node.parent;
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continue;
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}
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break;
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}
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return null;
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}
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/**
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* Checks if an expression is a variable that can only be observed within the given function.
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* @param {Variable|null} variable The variable to check
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* @param {boolean} isMemberAccess If `true` then this is a member access.
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* @returns {boolean} `true` if the variable is local to the given function, and is never referenced in a closure.
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*/
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function isLocalVariableWithoutEscape(variable, isMemberAccess) {
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if (!variable) {
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return false; // A global variable which was not defined.
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}
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// If the reference is a property access and the variable is a parameter, it handles the variable is not local.
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if (isMemberAccess && variable.defs.some(d => d.type === "Parameter")) {
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return false;
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}
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const functionScope = variable.scope.variableScope;
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return variable.references.every(reference =>
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reference.from.variableScope === functionScope);
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}
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class SegmentInfo {
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constructor() {
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this.info = new WeakMap();
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}
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/**
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* Initialize the segment information.
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* @param {PathSegment} segment The segment to initialize.
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* @returns {void}
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*/
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initialize(segment) {
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const outdatedReadVariableNames = new Set();
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const freshReadVariableNames = new Set();
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for (const prevSegment of segment.prevSegments) {
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const info = this.info.get(prevSegment);
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if (info) {
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info.outdatedReadVariableNames.forEach(Set.prototype.add, outdatedReadVariableNames);
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info.freshReadVariableNames.forEach(Set.prototype.add, freshReadVariableNames);
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}
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}
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this.info.set(segment, { outdatedReadVariableNames, freshReadVariableNames });
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}
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/**
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* Mark a given variable as read on given segments.
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* @param {PathSegment[]} segments The segments that it read the variable on.
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* @param {string} variableName The variable name to be read.
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* @returns {void}
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*/
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markAsRead(segments, variableName) {
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for (const segment of segments) {
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const info = this.info.get(segment);
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if (info) {
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info.freshReadVariableNames.add(variableName);
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}
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}
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}
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/**
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* Move `freshReadVariableNames` to `outdatedReadVariableNames`.
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* @param {PathSegment[]} segments The segments to process.
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* @returns {void}
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*/
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makeOutdated(segments) {
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for (const segment of segments) {
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const info = this.info.get(segment);
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if (info) {
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info.freshReadVariableNames.forEach(Set.prototype.add, info.outdatedReadVariableNames);
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info.freshReadVariableNames.clear();
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}
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}
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}
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/**
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* Check if a given variable is outdated on the current segments.
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* @param {PathSegment[]} segments The current segments.
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* @param {string} variableName The variable name to check.
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* @returns {boolean} `true` if the variable is outdated on the segments.
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*/
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isOutdated(segments, variableName) {
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for (const segment of segments) {
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const info = this.info.get(segment);
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if (info && info.outdatedReadVariableNames.has(variableName)) {
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return true;
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}
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}
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return false;
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}
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "problem",
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docs: {
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description: "disallow assignments that can lead to race conditions due to usage of `await` or `yield`",
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category: "Possible Errors",
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recommended: false,
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url: "https://eslint.org/docs/rules/require-atomic-updates"
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},
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fixable: null,
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schema: [],
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messages: {
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nonAtomicUpdate: "Possible race condition: `{{value}}` might be reassigned based on an outdated value of `{{value}}`."
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}
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},
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create(context) {
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const sourceCode = context.getSourceCode();
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const assignmentReferences = new Map();
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const segmentInfo = new SegmentInfo();
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let stack = null;
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return {
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onCodePathStart(codePath) {
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const scope = context.getScope();
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const shouldVerify =
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scope.type === "function" &&
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(scope.block.async || scope.block.generator);
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stack = {
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upper: stack,
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codePath,
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referenceMap: shouldVerify ? createReferenceMap(scope) : null
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};
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},
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onCodePathEnd() {
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stack = stack.upper;
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},
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// Initialize the segment information.
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onCodePathSegmentStart(segment) {
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segmentInfo.initialize(segment);
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},
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// Handle references to prepare verification.
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Identifier(node) {
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const { codePath, referenceMap } = stack;
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const reference = referenceMap && referenceMap.get(node);
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// Ignore if this is not a valid variable reference.
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if (!reference) {
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return;
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}
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const name = reference.identifier.name;
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const variable = reference.resolved;
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const writeExpr = getWriteExpr(reference);
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const isMemberAccess = reference.identifier.parent.type === "MemberExpression";
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// Add a fresh read variable.
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if (reference.isRead() && !(writeExpr && writeExpr.parent.operator === "=")) {
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segmentInfo.markAsRead(codePath.currentSegments, name);
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}
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/*
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* Register the variable to verify after ESLint traversed the `writeExpr` node
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* if this reference is an assignment to a variable which is referred from other clausure.
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*/
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if (writeExpr &&
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writeExpr.parent.right === writeExpr && // ← exclude variable declarations.
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!isLocalVariableWithoutEscape(variable, isMemberAccess)
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) {
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let refs = assignmentReferences.get(writeExpr);
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if (!refs) {
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refs = [];
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assignmentReferences.set(writeExpr, refs);
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}
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refs.push(reference);
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}
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},
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/*
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* Verify assignments.
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* If the reference exists in `outdatedReadVariableNames` list, report it.
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*/
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":expression:exit"(node) {
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const { codePath, referenceMap } = stack;
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// referenceMap exists if this is in a resumable function scope.
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if (!referenceMap) {
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return;
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}
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// Mark the read variables on this code path as outdated.
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if (node.type === "AwaitExpression" || node.type === "YieldExpression") {
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segmentInfo.makeOutdated(codePath.currentSegments);
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}
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// Verify.
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const references = assignmentReferences.get(node);
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if (references) {
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assignmentReferences.delete(node);
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for (const reference of references) {
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const name = reference.identifier.name;
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if (segmentInfo.isOutdated(codePath.currentSegments, name)) {
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context.report({
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node: node.parent,
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messageId: "nonAtomicUpdate",
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data: {
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value: sourceCode.getText(node.parent.left)
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}
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});
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}
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}
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}
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}
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};
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}
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};
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