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326 rivejä
12 KiB
326 rivejä
12 KiB
'use strict';
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/*
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* relax complexity and max-statements eslint rules in order to preserve the imported
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* core eslint `prefer-arrow-callback` rule code so that future updates to that code
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* can be more easily applied here.
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*/
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/* eslint "complexity": [ "error", 18 ], "max-statements": [ "error", 15 ] */
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/**
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* @fileoverview A rule to suggest using arrow functions as callbacks.
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* @author Toru Nagashima (core eslint rule)
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* @author Michael Fields (mocha-aware rule modifications)
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*/
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const createAstUtils = require('../util/ast');
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// ------------------------------------------------------------------------------
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// Helpers
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// ------------------------------------------------------------------------------
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/**
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* Checks whether or not a given variable is a function name.
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* @param {eslint-scope.Variable} variable - A variable to check.
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* @returns {boolean} `true` if the variable is a function name.
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*/
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function isFunctionName(variable) {
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return variable && variable.defs[0].type === 'FunctionName';
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}
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/**
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* Gets the variable object of `arguments` which is defined implicitly.
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* @param {eslint-scope.Scope} scope - A scope to get.
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* @returns {eslint-scope.Variable} The found variable object.
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*/
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function getVariableOfArguments(scope) {
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const variables = scope.variables;
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let variableObject = null;
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for (let i = 0; i < variables.length; i += 1) {
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const variable = variables[i];
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/*
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* If there was a parameter which is named "arguments", the
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* implicit "arguments" is not defined.
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* So does fast return with null.
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*/
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if (variable.name === 'arguments' && variable.identifiers.length === 0) {
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variableObject = variable;
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break;
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}
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}
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return variableObject;
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}
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/**
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* Does the node property indicate a `bind` identifier
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* @param {object} property - the node property.
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* @returns {boolean}
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*/
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function propertyIndicatesBind(property) {
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return !property.computed &&
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property.type === 'Identifier' &&
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property.name === 'bind';
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}
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/**
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* Is the node a `.bind(this)` node?
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* @param {ASTNode} node - the node property.
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* @returns {boolean}
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*/
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function isBindThis(node, currentNode) {
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return node.object === currentNode &&
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propertyIndicatesBind(node.property) &&
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node.parent.type === 'CallExpression' &&
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node.parent.callee === node;
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}
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/**
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* Checks whether a simple list of parameters contains any duplicates. This does not handle complex
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* parameter lists (e.g. with destructuring), since complex parameter lists are a SyntaxError with duplicate
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* parameter names anyway. Instead, it always returns `false` for complex parameter lists.
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* @param {ASTNode[]} paramsList The list of parameters for a function
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* @returns {boolean} `true` if the list of parameters contains any duplicates
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*/
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function hasDuplicateParams(paramsList) {
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return paramsList.every((param) => param.type === 'Identifier') &&
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paramsList.length !== new Set(paramsList.map((param) => param.name)).size;
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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: 'suggestion',
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docs: {
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description: 'Require using arrow functions for callbacks',
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category: 'ECMAScript 6',
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recommended: false,
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url: 'https://eslint.org/docs/rules/prefer-arrow-callback'
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},
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schema: [
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{
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type: 'object',
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properties: {
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allowNamedFunctions: {
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type: 'boolean'
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},
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allowUnboundThis: {
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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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fixable: 'code'
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},
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create(context) {
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const astUtils = createAstUtils(context.settings);
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const options = context.options[0] || {};
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// allowUnboundThis defaults to true
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const allowUnboundThis = options.allowUnboundThis !== false;
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const allowNamedFunctions = options.allowNamedFunctions;
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const sourceCode = context.getSourceCode();
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/**
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* Checkes whether or not a given node is a callback.
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* @param {ASTNode} node - A node to check.
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* @param {object} context - The eslint context.
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* @returns {Object}
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* {boolean} retv.isCallback - `true` if the node is a callback.
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* {boolean} retv.isMochaCallback - `true` if the node is an argument to a mocha function.
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* {boolean} retv.isLexicalThis - `true` if the node is with `.bind(this)`.
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*/
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function getCallbackInfo(node) {
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const retv = { isCallback: false, isLexicalThis: false };
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let searchComplete = false;
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let currentNode = node;
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let parent = node.parent;
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while (currentNode && !searchComplete) {
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switch (parent.type) {
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// Checks parents recursively.
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case 'LogicalExpression':
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case 'ConditionalExpression':
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break;
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// Checks whether the parent node is `.bind(this)` call.
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case 'MemberExpression':
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if (isBindThis(parent, currentNode)) {
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retv.isLexicalThis =
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parent.parent.arguments.length === 1 &&
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parent.parent.arguments[0].type === 'ThisExpression';
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parent = parent.parent;
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} else {
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searchComplete = true;
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}
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break;
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// Checks whether the node is a callback.
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case 'CallExpression':
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case 'NewExpression':
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if (parent.callee !== currentNode) {
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retv.isCallback = true;
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}
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// Checks whether the node is a mocha function callback.
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if (retv.isCallback && astUtils.isMochaFunctionCall(parent, context.getScope())) {
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retv.isMochaCallback = true;
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}
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searchComplete = true;
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break;
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default:
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searchComplete = true;
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}
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if (!searchComplete) {
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currentNode = parent;
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parent = parent.parent;
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}
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}
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return retv;
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}
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/*
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* {Array<{this: boolean, meta: boolean}>}
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* - this - A flag which shows there are one or more ThisExpression.
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* - meta - A flag which shows there are one or more MetaProperty.
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*/
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let stack = [];
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/**
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* Pushes new function scope with all `false` flags.
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* @returns {void}
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*/
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function enterScope() {
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stack.push({ this: false, meta: false });
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}
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/**
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* Pops a function scope from the stack.
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* @returns {{this: boolean, meta: boolean}} The information of the last scope.
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*/
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function exitScope() {
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return stack.pop();
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}
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return {
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// Reset internal state.
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Program() {
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stack = [];
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},
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// If there are below, it cannot replace with arrow functions merely.
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ThisExpression() {
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const info = stack[stack.length - 1];
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if (info) {
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info.this = true;
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}
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},
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MetaProperty() {
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const info = stack[stack.length - 1];
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info.meta = true;
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},
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// To skip nested scopes.
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FunctionDeclaration: enterScope,
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'FunctionDeclaration:exit': exitScope,
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// Main.
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FunctionExpression: enterScope,
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'FunctionExpression:exit'(node) {
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const scopeInfo = exitScope();
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// Skip named function expressions
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if (allowNamedFunctions && node.id && node.id.name) {
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return;
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}
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// Skip generators.
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if (node.generator) {
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return;
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}
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// Skip recursive functions.
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const nameVar = context.getDeclaredVariables(node)[0];
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if (isFunctionName(nameVar) && nameVar.references.length > 0) {
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return;
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}
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// Skip if it's using arguments.
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const variable = getVariableOfArguments(context.getScope());
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if (variable && variable.references.length > 0) {
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return;
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}
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// Reports if it's a callback which can replace with arrows.
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const callbackInfo = getCallbackInfo(node, context);
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if (callbackInfo.isCallback &&
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(!allowUnboundThis || !scopeInfo.this || callbackInfo.isLexicalThis) &&
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!scopeInfo.meta &&
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!callbackInfo.isMochaCallback
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) {
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context.report({
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node,
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message: 'Unexpected function expression.',
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fix(fixer) {
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if (!callbackInfo.isLexicalThis && scopeInfo.this || hasDuplicateParams(node.params)) {
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/*
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* If the callback function does not have .bind(this) and contains a reference to
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* `this`, there is no way to determine what `this` should be, so don't perform any
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* fixes. If the callback function has duplicates in its list of parameters (possible
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* in sloppy mode), don't replace it with an arrow function, because this is a
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* SyntaxError with arrow functions.
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*/
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return null;
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}
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const paramsLeftParen = node.params.length ?
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sourceCode.getTokenBefore(node.params[0]) :
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sourceCode.getTokenBefore(node.body, 1);
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const paramsRightParen = sourceCode.getTokenBefore(node.body);
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const asyncKeyword = node.async ? 'async ' : '';
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const paramsFullText = sourceCode.text.slice(
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paramsLeftParen.range[0], paramsRightParen.range[1]
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);
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const arrowFunctionText =
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`${asyncKeyword}${paramsFullText} => ${sourceCode.getText(node.body)}`;
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/*
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* If the callback function has `.bind(this)`, replace it with an arrow function and remove
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* the binding. Otherwise, just replace the arrow function itself.
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*/
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const replacedNode = callbackInfo.isLexicalThis ? node.parent.parent : node;
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/*
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* If the replaced node is part of a BinaryExpression, LogicalExpression, or
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* MemberExpression, then the arrow function needs to be parenthesized, because
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* `foo || () => {}` is invalid syntax even though `foo || function() {}` is valid.
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*/
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const needsParens = replacedNode.parent.type !== 'CallExpression' &&
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replacedNode.parent.type !== 'ConditionalExpression';
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const replacementText = needsParens ? `(${arrowFunctionText})` : arrowFunctionText;
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return fixer.replaceText(replacedNode, replacementText);
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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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