1 | /**
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2 | * @fileoverview Rule to enforce return statements in callbacks of array's methods
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3 | * @author Toru Nagashima
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4 | */
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5 |
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6 | ;
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7 |
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8 | //------------------------------------------------------------------------------
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9 | // Requirements
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10 | //------------------------------------------------------------------------------
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11 |
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12 | const lodash = require("lodash");
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13 |
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14 | const astUtils = require("../ast-utils");
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15 |
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16 | //------------------------------------------------------------------------------
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17 | // Helpers
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18 | //------------------------------------------------------------------------------
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19 |
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20 | const TARGET_NODE_TYPE = /^(?:Arrow)?FunctionExpression$/;
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21 | const TARGET_METHODS = /^(?:every|filter|find(?:Index)?|map|reduce(?:Right)?|some|sort)$/;
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22 |
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23 | /**
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24 | * Checks a given code path segment is reachable.
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25 | *
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26 | * @param {CodePathSegment} segment - A segment to check.
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27 | * @returns {boolean} `true` if the segment is reachable.
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28 | */
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29 | function isReachable(segment) {
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30 | return segment.reachable;
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31 | }
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32 |
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33 | /**
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34 | * Gets a readable location.
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35 | *
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36 | * - FunctionExpression -> the function name or `function` keyword.
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37 | * - ArrowFunctionExpression -> `=>` token.
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38 | *
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39 | * @param {ASTNode} node - A function node to get.
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40 | * @param {SourceCode} sourceCode - A source code to get tokens.
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41 | * @returns {ASTNode|Token} The node or the token of a location.
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42 | */
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43 | function getLocation(node, sourceCode) {
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44 | if (node.type === "ArrowFunctionExpression") {
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45 | return sourceCode.getTokenBefore(node.body);
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46 | }
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47 | return node.id || node;
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48 | }
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49 |
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50 | /**
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51 | * Checks a given node is a MemberExpression node which has the specified name's
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52 | * property.
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53 | *
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54 | * @param {ASTNode} node - A node to check.
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55 | * @returns {boolean} `true` if the node is a MemberExpression node which has
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56 | * the specified name's property
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57 | */
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58 | function isTargetMethod(node) {
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59 | return (
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60 | node.type === "MemberExpression" &&
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61 | TARGET_METHODS.test(astUtils.getStaticPropertyName(node) || "")
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62 | );
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63 | }
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64 |
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65 | /**
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66 | * Checks whether or not a given node is a function expression which is the
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67 | * callback of an array method.
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68 | *
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69 | * @param {ASTNode} node - A node to check. This is one of
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70 | * FunctionExpression or ArrowFunctionExpression.
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71 | * @returns {boolean} `true` if the node is the callback of an array method.
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72 | */
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73 | function isCallbackOfArrayMethod(node) {
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74 | while (node) {
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75 | const parent = node.parent;
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76 |
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77 | switch (parent.type) {
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78 |
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79 | /*
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80 | * Looks up the destination. e.g.,
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81 | * foo.every(nativeFoo || function foo() { ... });
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82 | */
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83 | case "LogicalExpression":
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84 | case "ConditionalExpression":
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85 | node = parent;
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86 | break;
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87 |
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88 | // If the upper function is IIFE, checks the destination of the return value.
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89 | // e.g.
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90 | // foo.every((function() {
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91 | // // setup...
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92 | // return function callback() { ... };
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93 | // })());
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94 | case "ReturnStatement": {
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95 | const func = astUtils.getUpperFunction(parent);
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96 |
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97 | if (func === null || !astUtils.isCallee(func)) {
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98 | return false;
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99 | }
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100 | node = func.parent;
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101 | break;
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102 | }
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103 |
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104 | // e.g.
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105 | // Array.from([], function() {});
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106 | // list.every(function() {});
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107 | case "CallExpression":
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108 | if (astUtils.isArrayFromMethod(parent.callee)) {
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109 | return (
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110 | parent.arguments.length >= 2 &&
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111 | parent.arguments[1] === node
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112 | );
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113 | }
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114 | if (isTargetMethod(parent.callee)) {
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115 | return (
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116 | parent.arguments.length >= 1 &&
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117 | parent.arguments[0] === node
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118 | );
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119 | }
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120 | return false;
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121 |
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122 | // Otherwise this node is not target.
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123 | default:
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124 | return false;
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125 | }
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126 | }
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127 |
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128 | /* istanbul ignore next: unreachable */
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129 | return false;
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130 | }
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131 |
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132 | //------------------------------------------------------------------------------
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133 | // Rule Definition
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134 | //------------------------------------------------------------------------------
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135 |
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136 | module.exports = {
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137 | meta: {
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138 | docs: {
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139 | description: "enforce `return` statements in callbacks of array methods",
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140 | category: "Best Practices",
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141 | recommended: false
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142 | },
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143 |
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144 | schema: []
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145 | },
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146 |
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147 | create(context) {
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148 | let funcInfo = {
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149 | upper: null,
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150 | codePath: null,
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151 | hasReturn: false,
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152 | shouldCheck: false,
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153 | node: null
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154 | };
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155 |
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156 | /**
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157 | * Checks whether or not the last code path segment is reachable.
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158 | * Then reports this function if the segment is reachable.
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159 | *
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160 | * If the last code path segment is reachable, there are paths which are not
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161 | * returned or thrown.
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162 | *
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163 | * @param {ASTNode} node - A node to check.
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164 | * @returns {void}
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165 | */
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166 | function checkLastSegment(node) {
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167 | if (funcInfo.shouldCheck &&
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168 | funcInfo.codePath.currentSegments.some(isReachable)
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169 | ) {
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170 | context.report({
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171 | node,
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172 | loc: getLocation(node, context.getSourceCode()).loc.start,
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173 | message: funcInfo.hasReturn
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174 | ? "Expected to return a value at the end of {{name}}."
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175 | : "Expected to return a value in {{name}}.",
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176 | data: {
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177 | name: astUtils.getFunctionNameWithKind(funcInfo.node)
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178 | }
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179 | });
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180 | }
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181 | }
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182 |
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183 | return {
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184 |
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185 | // Stacks this function's information.
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186 | onCodePathStart(codePath, node) {
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187 | funcInfo = {
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188 | upper: funcInfo,
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189 | codePath,
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190 | hasReturn: false,
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191 | shouldCheck:
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192 | TARGET_NODE_TYPE.test(node.type) &&
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193 | node.body.type === "BlockStatement" &&
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194 | isCallbackOfArrayMethod(node) &&
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195 | !node.async &&
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196 | !node.generator,
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197 | node
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198 | };
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199 | },
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200 |
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201 | // Pops this function's information.
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202 | onCodePathEnd() {
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203 | funcInfo = funcInfo.upper;
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204 | },
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205 |
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206 | // Checks the return statement is valid.
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207 | ReturnStatement(node) {
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208 | if (funcInfo.shouldCheck) {
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209 | funcInfo.hasReturn = true;
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210 |
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211 | if (!node.argument) {
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212 | context.report({
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213 | node,
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214 | message: "{{name}} expected a return value.",
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215 | data: {
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216 | name: lodash.upperFirst(astUtils.getFunctionNameWithKind(funcInfo.node))
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217 | }
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218 | });
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219 | }
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220 | }
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221 | },
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222 |
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223 | // Reports a given function if the last path is reachable.
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224 | "FunctionExpression:exit": checkLastSegment,
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225 | "ArrowFunctionExpression:exit": checkLastSegment
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226 | };
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227 | }
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228 | };
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