1 | /**
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2 | * @fileoverview Disallow reassignment of function parameters.
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3 | * @author Nat Burns
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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 | // Rule Definition
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9 | //------------------------------------------------------------------------------
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10 |
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11 | const stopNodePattern = /(?:Statement|Declaration|Function(?:Expression)?|Program)$/;
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12 |
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13 | module.exports = {
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14 | meta: {
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15 | docs: {
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16 | description: "disallow reassigning `function` parameters",
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17 | category: "Best Practices",
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18 | recommended: false,
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19 | url: "https://eslint.org/docs/rules/no-param-reassign"
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20 | },
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21 |
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22 | schema: [
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23 | {
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24 | oneOf: [
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25 | {
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26 | type: "object",
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27 | properties: {
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28 | props: {
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29 | enum: [false]
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30 | }
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31 | },
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32 | additionalProperties: false
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33 | },
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34 | {
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35 | type: "object",
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36 | properties: {
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37 | props: {
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38 | enum: [true]
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39 | },
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40 | ignorePropertyModificationsFor: {
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41 | type: "array",
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42 | items: {
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43 | type: "string"
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44 | },
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45 | uniqueItems: true
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46 | }
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47 | },
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48 | additionalProperties: false
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49 | }
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50 | ]
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51 | }
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52 | ]
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53 | },
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54 |
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55 | create(context) {
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56 | const props = context.options[0] && Boolean(context.options[0].props);
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57 | const ignoredPropertyAssignmentsFor = context.options[0] && context.options[0].ignorePropertyModificationsFor || [];
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58 |
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59 | /**
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60 | * Checks whether or not the reference modifies properties of its variable.
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61 | * @param {Reference} reference - A reference to check.
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62 | * @returns {boolean} Whether or not the reference modifies properties of its variable.
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63 | */
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64 | function isModifyingProp(reference) {
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65 | let node = reference.identifier;
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66 | let parent = node.parent;
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67 |
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68 | while (parent && !stopNodePattern.test(parent.type)) {
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69 | switch (parent.type) {
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70 |
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71 | // e.g. foo.a = 0;
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72 | case "AssignmentExpression":
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73 | return parent.left === node;
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74 |
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75 | // e.g. ++foo.a;
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76 | case "UpdateExpression":
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77 | return true;
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78 |
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79 | // e.g. delete foo.a;
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80 | case "UnaryExpression":
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81 | if (parent.operator === "delete") {
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82 | return true;
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83 | }
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84 | break;
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85 |
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86 | // EXCLUDES: e.g. cache.get(foo.a).b = 0;
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87 | case "CallExpression":
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88 | if (parent.callee !== node) {
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89 | return false;
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90 | }
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91 | break;
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92 |
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93 | // EXCLUDES: e.g. cache[foo.a] = 0;
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94 | case "MemberExpression":
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95 | if (parent.property === node) {
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96 | return false;
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97 | }
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98 | break;
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99 |
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100 | // EXCLUDES: e.g. ({ [foo]: a }) = bar;
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101 | case "Property":
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102 | if (parent.key === node) {
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103 | return false;
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104 | }
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105 |
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106 | break;
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107 |
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108 | // no default
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109 | }
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110 |
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111 | node = parent;
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112 | parent = node.parent;
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113 | }
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114 |
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115 | return false;
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116 | }
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117 |
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118 | /**
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119 | * Reports a reference if is non initializer and writable.
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120 | * @param {Reference} reference - A reference to check.
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121 | * @param {int} index - The index of the reference in the references.
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122 | * @param {Reference[]} references - The array that the reference belongs to.
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123 | * @returns {void}
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124 | */
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125 | function checkReference(reference, index, references) {
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126 | const identifier = reference.identifier;
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127 |
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128 | if (identifier &&
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129 | !reference.init &&
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130 |
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131 | /*
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132 | * Destructuring assignments can have multiple default value,
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133 | * so possibly there are multiple writeable references for the same identifier.
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134 | */
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135 | (index === 0 || references[index - 1].identifier !== identifier)
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136 | ) {
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137 | if (reference.isWrite()) {
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138 | context.report({ node: identifier, message: "Assignment to function parameter '{{name}}'.", data: { name: identifier.name } });
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139 | } else if (props && isModifyingProp(reference) && ignoredPropertyAssignmentsFor.indexOf(identifier.name) === -1) {
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140 | context.report({ node: identifier, message: "Assignment to property of function parameter '{{name}}'.", data: { name: identifier.name } });
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141 | }
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142 | }
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143 | }
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144 |
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145 | /**
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146 | * Finds and reports references that are non initializer and writable.
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147 | * @param {Variable} variable - A variable to check.
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148 | * @returns {void}
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149 | */
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150 | function checkVariable(variable) {
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151 | if (variable.defs[0].type === "Parameter") {
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152 | variable.references.forEach(checkReference);
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153 | }
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154 | }
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155 |
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156 | /**
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157 | * Checks parameters of a given function node.
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158 | * @param {ASTNode} node - A function node to check.
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159 | * @returns {void}
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160 | */
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161 | function checkForFunction(node) {
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162 | context.getDeclaredVariables(node).forEach(checkVariable);
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163 | }
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164 |
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165 | return {
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166 |
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167 | // `:exit` is needed for the `node.parent` property of identifier nodes.
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168 | "FunctionDeclaration:exit": checkForFunction,
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169 | "FunctionExpression:exit": checkForFunction,
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170 | "ArrowFunctionExpression:exit": checkForFunction
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171 | };
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172 |
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173 | }
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174 | };
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