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