1 | /**
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2 | * @fileoverview Rule to flag consistent return values
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3 | * @author Nicholas C. Zakas
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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 | // Requirements
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9 | //------------------------------------------------------------------------------
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10 |
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11 | const lodash = require("lodash");
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12 |
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13 | const astUtils = require("../ast-utils");
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14 |
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15 | //------------------------------------------------------------------------------
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16 | // Helpers
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17 | //------------------------------------------------------------------------------
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18 |
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19 | /**
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20 | * Checks whether or not a given node is an `Identifier` node which was named a given name.
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21 | * @param {ASTNode} node - A node to check.
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22 | * @param {string} name - An expected name of the node.
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23 | * @returns {boolean} `true` if the node is an `Identifier` node which was named as expected.
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24 | */
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25 | function isIdentifier(node, name) {
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26 | return node.type === "Identifier" && node.name === name;
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27 | }
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28 |
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29 | /**
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30 | * Checks whether or not a given code path segment is unreachable.
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31 | * @param {CodePathSegment} segment - A CodePathSegment to check.
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32 | * @returns {boolean} `true` if the segment is unreachable.
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33 | */
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34 | function isUnreachable(segment) {
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35 | return !segment.reachable;
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36 | }
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37 |
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38 | /**
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39 | * Checks whether a given node is a `constructor` method in an ES6 class
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40 | * @param {ASTNode} node A node to check
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41 | * @returns {boolean} `true` if the node is a `constructor` method
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42 | */
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43 | function isClassConstructor(node) {
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44 | return node.type === "FunctionExpression" &&
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45 | node.parent &&
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46 | node.parent.type === "MethodDefinition" &&
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47 | node.parent.kind === "constructor";
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48 | }
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49 |
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50 | //------------------------------------------------------------------------------
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51 | // Rule Definition
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52 | //------------------------------------------------------------------------------
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53 |
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54 | module.exports = {
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55 | meta: {
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56 | docs: {
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57 | description: "require `return` statements to either always or never specify values",
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58 | category: "Best Practices",
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59 | recommended: false
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60 | },
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61 |
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62 | schema: [{
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63 | type: "object",
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64 | properties: {
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65 | treatUndefinedAsUnspecified: {
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66 | type: "boolean"
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67 | }
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68 | },
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69 | additionalProperties: false
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70 | }]
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71 | },
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72 |
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73 | create(context) {
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74 | const options = context.options[0] || {};
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75 | const treatUndefinedAsUnspecified = options.treatUndefinedAsUnspecified === true;
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76 | let funcInfo = null;
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77 |
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78 | /**
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79 | * Checks whether of not the implicit returning is consistent if the last
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80 | * code path segment is reachable.
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81 | *
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82 | * @param {ASTNode} node - A program/function node to check.
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83 | * @returns {void}
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84 | */
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85 | function checkLastSegment(node) {
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86 | let loc, name;
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87 |
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88 | /*
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89 | * Skip if it expected no return value or unreachable.
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90 | * When unreachable, all paths are returned or thrown.
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91 | */
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92 | if (!funcInfo.hasReturnValue ||
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93 | funcInfo.codePath.currentSegments.every(isUnreachable) ||
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94 | astUtils.isES5Constructor(node) ||
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95 | isClassConstructor(node)
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96 | ) {
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97 | return;
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98 | }
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99 |
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100 | // Adjust a location and a message.
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101 | if (node.type === "Program") {
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102 |
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103 | // The head of program.
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104 | loc = { line: 1, column: 0 };
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105 | name = "program";
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106 | } else if (node.type === "ArrowFunctionExpression") {
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107 |
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108 | // `=>` token
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109 | loc = context.getSourceCode().getTokenBefore(node.body, astUtils.isArrowToken).loc.start;
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110 | } else if (
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111 | node.parent.type === "MethodDefinition" ||
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112 | (node.parent.type === "Property" && node.parent.method)
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113 | ) {
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114 |
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115 | // Method name.
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116 | loc = node.parent.key.loc.start;
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117 | } else {
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118 |
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119 | // Function name or `function` keyword.
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120 | loc = (node.id || node).loc.start;
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121 | }
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122 |
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123 | if (!name) {
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124 | name = astUtils.getFunctionNameWithKind(node);
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125 | }
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126 |
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127 | // Reports.
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128 | context.report({
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129 | node,
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130 | loc,
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131 | message: "Expected to return a value at the end of {{name}}.",
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132 | data: { name }
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133 | });
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134 | }
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135 |
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136 | return {
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137 |
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138 | // Initializes/Disposes state of each code path.
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139 | onCodePathStart(codePath, node) {
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140 | funcInfo = {
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141 | upper: funcInfo,
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142 | codePath,
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143 | hasReturn: false,
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144 | hasReturnValue: false,
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145 | message: "",
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146 | node
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147 | };
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148 | },
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149 | onCodePathEnd() {
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150 | funcInfo = funcInfo.upper;
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151 | },
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152 |
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153 | // Reports a given return statement if it's inconsistent.
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154 | ReturnStatement(node) {
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155 | const argument = node.argument;
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156 | let hasReturnValue = Boolean(argument);
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157 |
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158 | if (treatUndefinedAsUnspecified && hasReturnValue) {
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159 | hasReturnValue = !isIdentifier(argument, "undefined") && argument.operator !== "void";
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160 | }
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161 |
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162 | if (!funcInfo.hasReturn) {
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163 | funcInfo.hasReturn = true;
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164 | funcInfo.hasReturnValue = hasReturnValue;
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165 | funcInfo.message = "{{name}} expected {{which}} return value.";
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166 | funcInfo.data = {
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167 | name: funcInfo.node.type === "Program"
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168 | ? "Program"
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169 | : lodash.upperFirst(astUtils.getFunctionNameWithKind(funcInfo.node)),
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170 | which: hasReturnValue ? "a" : "no"
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171 | };
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172 | } else if (funcInfo.hasReturnValue !== hasReturnValue) {
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173 | context.report({
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174 | node,
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175 | message: funcInfo.message,
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176 | data: funcInfo.data
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177 | });
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178 | }
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179 | },
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180 |
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181 | // Reports a given program/function if the implicit returning is not consistent.
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182 | "Program:exit": checkLastSegment,
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183 | "FunctionDeclaration:exit": checkLastSegment,
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184 | "FunctionExpression:exit": checkLastSegment,
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185 | "ArrowFunctionExpression:exit": checkLastSegment
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186 | };
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187 | }
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188 | };
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