477 lines
21 KiB
JavaScript
477 lines
21 KiB
JavaScript
/**
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* @fileoverview Rule to replace assignment expressions with logical operator assignment
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* @author Daniel Martens
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Requirements
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//------------------------------------------------------------------------------
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const astUtils = require("./utils/ast-utils.js");
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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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const baseTypes = new Set(["Identifier", "Super", "ThisExpression"]);
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/**
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* Returns true iff either "undefined" or a void expression (eg. "void 0")
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* @param {ASTNode} expression Expression to check
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* @param {import('eslint-scope').Scope} scope Scope of the expression
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* @returns {boolean} True iff "undefined" or "void ..."
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*/
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function isUndefined(expression, scope) {
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if (expression.type === "Identifier" && expression.name === "undefined") {
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return astUtils.isReferenceToGlobalVariable(scope, expression);
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}
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return expression.type === "UnaryExpression" &&
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expression.operator === "void" &&
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expression.argument.type === "Literal" &&
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expression.argument.value === 0;
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}
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/**
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* Returns true iff the reference is either an identifier or member expression
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* @param {ASTNode} expression Expression to check
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* @returns {boolean} True for identifiers and member expressions
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*/
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function isReference(expression) {
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return (expression.type === "Identifier" && expression.name !== "undefined") ||
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expression.type === "MemberExpression";
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}
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/**
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* Returns true iff the expression checks for nullish with loose equals.
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* Examples: value == null, value == void 0
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* @param {ASTNode} expression Test condition
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* @param {import('eslint-scope').Scope} scope Scope of the expression
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* @returns {boolean} True iff implicit nullish comparison
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*/
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function isImplicitNullishComparison(expression, scope) {
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if (expression.type !== "BinaryExpression" || expression.operator !== "==") {
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return false;
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}
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const reference = isReference(expression.left) ? "left" : "right";
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const nullish = reference === "left" ? "right" : "left";
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return isReference(expression[reference]) &&
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(astUtils.isNullLiteral(expression[nullish]) || isUndefined(expression[nullish], scope));
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}
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/**
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* Condition with two equal comparisons.
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* @param {ASTNode} expression Condition
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* @returns {boolean} True iff matches ? === ? || ? === ?
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*/
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function isDoubleComparison(expression) {
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return expression.type === "LogicalExpression" &&
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expression.operator === "||" &&
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expression.left.type === "BinaryExpression" &&
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expression.left.operator === "===" &&
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expression.right.type === "BinaryExpression" &&
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expression.right.operator === "===";
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}
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/**
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* Returns true iff the expression checks for undefined and null.
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* Example: value === null || value === undefined
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* @param {ASTNode} expression Test condition
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* @param {import('eslint-scope').Scope} scope Scope of the expression
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* @returns {boolean} True iff explicit nullish comparison
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*/
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function isExplicitNullishComparison(expression, scope) {
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if (!isDoubleComparison(expression)) {
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return false;
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}
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const leftReference = isReference(expression.left.left) ? "left" : "right";
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const leftNullish = leftReference === "left" ? "right" : "left";
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const rightReference = isReference(expression.right.left) ? "left" : "right";
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const rightNullish = rightReference === "left" ? "right" : "left";
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return astUtils.isSameReference(expression.left[leftReference], expression.right[rightReference]) &&
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((astUtils.isNullLiteral(expression.left[leftNullish]) && isUndefined(expression.right[rightNullish], scope)) ||
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(isUndefined(expression.left[leftNullish], scope) && astUtils.isNullLiteral(expression.right[rightNullish])));
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}
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/**
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* Returns true for Boolean(arg) calls
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* @param {ASTNode} expression Test condition
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* @param {import('eslint-scope').Scope} scope Scope of the expression
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* @returns {boolean} Whether the expression is a boolean cast
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*/
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function isBooleanCast(expression, scope) {
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return expression.type === "CallExpression" &&
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expression.callee.name === "Boolean" &&
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expression.arguments.length === 1 &&
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astUtils.isReferenceToGlobalVariable(scope, expression.callee);
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}
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/**
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* Returns true for:
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* truthiness checks: value, Boolean(value), !!value
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* falsiness checks: !value, !Boolean(value)
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* nullish checks: value == null, value === undefined || value === null
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* @param {ASTNode} expression Test condition
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* @param {import('eslint-scope').Scope} scope Scope of the expression
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* @returns {?{ reference: ASTNode, operator: '??'|'||'|'&&'}} Null if not a known existence
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*/
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function getExistence(expression, scope) {
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const isNegated = expression.type === "UnaryExpression" && expression.operator === "!";
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const base = isNegated ? expression.argument : expression;
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switch (true) {
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case isReference(base):
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return { reference: base, operator: isNegated ? "||" : "&&" };
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case base.type === "UnaryExpression" && base.operator === "!" && isReference(base.argument):
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return { reference: base.argument, operator: "&&" };
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case isBooleanCast(base, scope) && isReference(base.arguments[0]):
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return { reference: base.arguments[0], operator: isNegated ? "||" : "&&" };
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case isImplicitNullishComparison(expression, scope):
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return { reference: isReference(expression.left) ? expression.left : expression.right, operator: "??" };
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case isExplicitNullishComparison(expression, scope):
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return { reference: isReference(expression.left.left) ? expression.left.left : expression.left.right, operator: "??" };
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default: return null;
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}
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}
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/**
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* Returns true iff the node is inside a with block
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* @param {ASTNode} node Node to check
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* @returns {boolean} True iff passed node is inside a with block
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*/
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function isInsideWithBlock(node) {
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if (node.type === "Program") {
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return false;
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}
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return node.parent.type === "WithStatement" && node.parent.body === node ? true : isInsideWithBlock(node.parent);
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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/** @type {import('../shared/types').Rule} */
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module.exports = {
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meta: {
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type: "suggestion",
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docs: {
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description: "Require or disallow logical assignment operator shorthand",
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recommended: false,
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url: "https://eslint.org/docs/latest/rules/logical-assignment-operators"
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},
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schema: {
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type: "array",
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oneOf: [{
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items: [
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{ const: "always" },
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{
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type: "object",
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properties: {
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enforceForIfStatements: {
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type: "boolean"
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}
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},
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additionalProperties: false
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}
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],
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minItems: 0, // 0 for allowing passing no options
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maxItems: 2
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}, {
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items: [{ const: "never" }],
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minItems: 1,
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maxItems: 1
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}]
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},
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fixable: "code",
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hasSuggestions: true,
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messages: {
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assignment: "Assignment (=) can be replaced with operator assignment ({{operator}}).",
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useLogicalOperator: "Convert this assignment to use the operator {{ operator }}.",
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logical: "Logical expression can be replaced with an assignment ({{ operator }}).",
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convertLogical: "Replace this logical expression with an assignment with the operator {{ operator }}.",
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if: "'if' statement can be replaced with a logical operator assignment with operator {{ operator }}.",
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convertIf: "Replace this 'if' statement with a logical assignment with operator {{ operator }}.",
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unexpected: "Unexpected logical operator assignment ({{operator}}) shorthand.",
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separate: "Separate the logical assignment into an assignment with a logical operator."
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}
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},
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create(context) {
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const mode = context.options[0] === "never" ? "never" : "always";
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const checkIf = mode === "always" && context.options.length > 1 && context.options[1].enforceForIfStatements;
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const sourceCode = context.sourceCode;
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const isStrict = sourceCode.getScope(sourceCode.ast).isStrict;
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/**
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* Returns false if the access could be a getter
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* @param {ASTNode} node Assignment expression
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* @returns {boolean} True iff the fix is safe
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*/
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function cannotBeGetter(node) {
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return node.type === "Identifier" &&
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(isStrict || !isInsideWithBlock(node));
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}
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/**
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* Check whether only a single property is accessed
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* @param {ASTNode} node reference
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* @returns {boolean} True iff a single property is accessed
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*/
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function accessesSingleProperty(node) {
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if (!isStrict && isInsideWithBlock(node)) {
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return node.type === "Identifier";
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}
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return node.type === "MemberExpression" &&
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baseTypes.has(node.object.type) &&
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(!node.computed || (node.property.type !== "MemberExpression" && node.property.type !== "ChainExpression"));
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}
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/**
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* Adds a fixer or suggestion whether on the fix is safe.
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* @param {{ messageId: string, node: ASTNode }} descriptor Report descriptor without fix or suggest
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* @param {{ messageId: string, fix: Function }} suggestion Adds the fix or the whole suggestion as only element in "suggest" to suggestion
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* @param {boolean} shouldBeFixed Fix iff the condition is true
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* @returns {Object} Descriptor with either an added fix or suggestion
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*/
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function createConditionalFixer(descriptor, suggestion, shouldBeFixed) {
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if (shouldBeFixed) {
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return {
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...descriptor,
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fix: suggestion.fix
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};
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}
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return {
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...descriptor,
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suggest: [suggestion]
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};
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}
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/**
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* Returns the operator token for assignments and binary expressions
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* @param {ASTNode} node AssignmentExpression or BinaryExpression
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* @returns {import('eslint').AST.Token} Operator token between the left and right expression
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*/
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function getOperatorToken(node) {
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return sourceCode.getFirstTokenBetween(node.left, node.right, token => token.value === node.operator);
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}
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if (mode === "never") {
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return {
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// foo ||= bar
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"AssignmentExpression"(assignment) {
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if (!astUtils.isLogicalAssignmentOperator(assignment.operator)) {
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return;
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}
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const descriptor = {
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messageId: "unexpected",
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node: assignment,
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data: { operator: assignment.operator }
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};
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const suggestion = {
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messageId: "separate",
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*fix(ruleFixer) {
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if (sourceCode.getCommentsInside(assignment).length > 0) {
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return;
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}
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const operatorToken = getOperatorToken(assignment);
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// -> foo = bar
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yield ruleFixer.replaceText(operatorToken, "=");
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const assignmentText = sourceCode.getText(assignment.left);
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const operator = assignment.operator.slice(0, -1);
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// -> foo = foo || bar
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yield ruleFixer.insertTextAfter(operatorToken, ` ${assignmentText} ${operator}`);
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const precedence = astUtils.getPrecedence(assignment.right) <= astUtils.getPrecedence({ type: "LogicalExpression", operator });
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// ?? and || / && cannot be mixed but have same precedence
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const mixed = assignment.operator === "??=" && astUtils.isLogicalExpression(assignment.right);
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if (!astUtils.isParenthesised(sourceCode, assignment.right) && (precedence || mixed)) {
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// -> foo = foo || (bar)
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yield ruleFixer.insertTextBefore(assignment.right, "(");
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yield ruleFixer.insertTextAfter(assignment.right, ")");
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}
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}
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};
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context.report(createConditionalFixer(descriptor, suggestion, cannotBeGetter(assignment.left)));
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}
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};
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}
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return {
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// foo = foo || bar
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"AssignmentExpression[operator='='][right.type='LogicalExpression']"(assignment) {
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if (!astUtils.isSameReference(assignment.left, assignment.right.left)) {
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return;
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}
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const descriptor = {
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messageId: "assignment",
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node: assignment,
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data: { operator: `${assignment.right.operator}=` }
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};
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const suggestion = {
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messageId: "useLogicalOperator",
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data: { operator: `${assignment.right.operator}=` },
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*fix(ruleFixer) {
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if (sourceCode.getCommentsInside(assignment).length > 0) {
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return;
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}
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// No need for parenthesis around the assignment based on precedence as the precedence stays the same even with changed operator
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const assignmentOperatorToken = getOperatorToken(assignment);
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// -> foo ||= foo || bar
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yield ruleFixer.insertTextBefore(assignmentOperatorToken, assignment.right.operator);
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// -> foo ||= bar
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const logicalOperatorToken = getOperatorToken(assignment.right);
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const firstRightOperandToken = sourceCode.getTokenAfter(logicalOperatorToken);
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yield ruleFixer.removeRange([assignment.right.range[0], firstRightOperandToken.range[0]]);
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}
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};
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context.report(createConditionalFixer(descriptor, suggestion, cannotBeGetter(assignment.left)));
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},
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// foo || (foo = bar)
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'LogicalExpression[right.type="AssignmentExpression"][right.operator="="]'(logical) {
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// Right side has to be parenthesized, otherwise would be parsed as (foo || foo) = bar which is illegal
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if (isReference(logical.left) && astUtils.isSameReference(logical.left, logical.right.left)) {
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const descriptor = {
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messageId: "logical",
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node: logical,
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data: { operator: `${logical.operator}=` }
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};
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const suggestion = {
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messageId: "convertLogical",
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data: { operator: `${logical.operator}=` },
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*fix(ruleFixer) {
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if (sourceCode.getCommentsInside(logical).length > 0) {
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return;
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}
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const parentPrecedence = astUtils.getPrecedence(logical.parent);
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const requiresOuterParenthesis = logical.parent.type !== "ExpressionStatement" && (
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parentPrecedence === -1 ||
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astUtils.getPrecedence({ type: "AssignmentExpression" }) < parentPrecedence
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);
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if (!astUtils.isParenthesised(sourceCode, logical) && requiresOuterParenthesis) {
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yield ruleFixer.insertTextBefore(logical, "(");
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yield ruleFixer.insertTextAfter(logical, ")");
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}
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// Also removes all opening parenthesis
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yield ruleFixer.removeRange([logical.range[0], logical.right.range[0]]); // -> foo = bar)
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// Also removes all ending parenthesis
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yield ruleFixer.removeRange([logical.right.range[1], logical.range[1]]); // -> foo = bar
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const operatorToken = getOperatorToken(logical.right);
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yield ruleFixer.insertTextBefore(operatorToken, logical.operator); // -> foo ||= bar
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}
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};
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const fix = cannotBeGetter(logical.left) || accessesSingleProperty(logical.left);
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context.report(createConditionalFixer(descriptor, suggestion, fix));
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}
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},
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// if (foo) foo = bar
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"IfStatement[alternate=null]"(ifNode) {
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if (!checkIf) {
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return;
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}
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const hasBody = ifNode.consequent.type === "BlockStatement";
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if (hasBody && ifNode.consequent.body.length !== 1) {
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return;
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}
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const body = hasBody ? ifNode.consequent.body[0] : ifNode.consequent;
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const scope = sourceCode.getScope(ifNode);
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const existence = getExistence(ifNode.test, scope);
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if (
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body.type === "ExpressionStatement" &&
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body.expression.type === "AssignmentExpression" &&
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body.expression.operator === "=" &&
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existence !== null &&
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astUtils.isSameReference(existence.reference, body.expression.left)
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) {
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const descriptor = {
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messageId: "if",
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node: ifNode,
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data: { operator: `${existence.operator}=` }
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};
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const suggestion = {
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messageId: "convertIf",
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data: { operator: `${existence.operator}=` },
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*fix(ruleFixer) {
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if (sourceCode.getCommentsInside(ifNode).length > 0) {
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return;
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}
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const firstBodyToken = sourceCode.getFirstToken(body);
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const prevToken = sourceCode.getTokenBefore(ifNode);
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if (
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prevToken !== null &&
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prevToken.value !== ";" &&
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prevToken.value !== "{" &&
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firstBodyToken.type !== "Identifier" &&
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firstBodyToken.type !== "Keyword"
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) {
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// Do not fix if the fixed statement could be part of the previous statement (eg. fn() if (a == null) (a) = b --> fn()(a) ??= b)
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return;
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}
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const operatorToken = getOperatorToken(body.expression);
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yield ruleFixer.insertTextBefore(operatorToken, existence.operator); // -> if (foo) foo ||= bar
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yield ruleFixer.removeRange([ifNode.range[0], body.range[0]]); // -> foo ||= bar
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yield ruleFixer.removeRange([body.range[1], ifNode.range[1]]); // -> foo ||= bar, only present if "if" had a body
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const nextToken = sourceCode.getTokenAfter(body.expression);
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if (hasBody && (nextToken !== null && nextToken.value !== ";")) {
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yield ruleFixer.insertTextAfter(ifNode, ";");
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}
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}
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};
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const shouldBeFixed = cannotBeGetter(existence.reference) ||
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(ifNode.test.type !== "LogicalExpression" && accessesSingleProperty(existence.reference));
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context.report(createConditionalFixer(descriptor, suggestion, shouldBeFixed));
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}
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}
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};
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}
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};
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