1 | /**
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2 | * @fileoverview Rule to replace assignment expressions with operator assignment
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3 | * @author Brandon Mills
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4 | * @copyright 2014 Brandon Mills. All rights reserved.
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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 | // Helpers
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10 | //------------------------------------------------------------------------------
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11 |
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12 | /**
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13 | * Checks whether an operator is commutative and has an operator assignment
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14 | * shorthand form.
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15 | * @param {string} operator Operator to check.
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16 | * @returns {boolean} True if the operator is commutative and has a
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17 | * shorthand form.
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18 | */
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19 | function isCommutativeOperatorWithShorthand(operator) {
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20 | return ["*", "&", "^", "|"].indexOf(operator) >= 0;
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21 | }
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22 |
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23 | /**
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24 | * Checks whether an operator is not commuatative and has an operator assignment
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25 | * shorthand form.
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26 | * @param {string} operator Operator to check.
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27 | * @returns {boolean} True if the operator is not commuatative and has
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28 | * a shorthand form.
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29 | */
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30 | function isNonCommutativeOperatorWithShorthand(operator) {
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31 | return ["+", "-", "/", "%", "<<", ">>", ">>>"].indexOf(operator) >= 0;
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32 | }
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33 |
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34 | //------------------------------------------------------------------------------
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35 | // Rule Definition
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36 | //------------------------------------------------------------------------------
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37 |
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38 | /**
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39 | * Checks whether two expressions reference the same value. For example:
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40 | * a = a
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41 | * a.b = a.b
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42 | * a[0] = a[0]
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43 | * a['b'] = a['b']
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44 | * @param {ASTNode} a Left side of the comparison.
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45 | * @param {ASTNode} b Right side of the comparison.
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46 | * @returns {boolean} True if both sides match and reference the same value.
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47 | */
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48 | function same(a, b) {
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49 | if (a.type !== b.type) {
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50 | return false;
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51 | }
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52 |
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53 | switch (a.type) {
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54 | case "Identifier":
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55 | return a.name === b.name;
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56 | case "Literal":
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57 | return a.value === b.value;
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58 | case "MemberExpression":
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59 | // x[0] = x[0]
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60 | // x[y] = x[y]
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61 | // x.y = x.y
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62 | return same(a.object, b.object) && same(a.property, b.property);
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63 | default:
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64 | return false;
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65 | }
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66 | }
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67 |
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68 | module.exports = function(context) {
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69 |
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70 | /**
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71 | * Ensures that an assignment uses the shorthand form where possible.
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72 | * @param {ASTNode} node An AssignmentExpression node.
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73 | * @returns {void}
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74 | */
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75 | function verify(node) {
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76 | var expr, left, operator;
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77 |
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78 | if (node.operator !== "=" || node.right.type !== "BinaryExpression") {
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79 | return;
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80 | }
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81 |
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82 | left = node.left;
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83 | expr = node.right;
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84 | operator = expr.operator;
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85 |
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86 | if (isCommutativeOperatorWithShorthand(operator)) {
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87 | if (same(left, expr.left) || same(left, expr.right)) {
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88 | context.report(node, "Assignment can be replaced with operator assignment.");
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89 | }
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90 | } else if (isNonCommutativeOperatorWithShorthand(operator)) {
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91 | if (same(left, expr.left)) {
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92 | context.report(node, "Assignment can be replaced with operator assignment.");
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93 | }
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94 | }
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95 | }
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96 |
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97 | /**
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98 | * Warns if an assignment expression uses operator assignment shorthand.
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99 | * @param {ASTNode} node An AssignmentExpression node.
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100 | * @returns {void}
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101 | */
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102 | function prohibit(node) {
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103 | if (node.operator !== "=") {
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104 | context.report(node, "Unexpected operator assignment shorthand.");
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105 | }
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106 | }
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107 |
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108 | return {
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109 | "AssignmentExpression": context.options[0] !== "never" ? verify : prohibit
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110 | };
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111 |
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112 | };
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113 |
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114 | module.exports.schema = [
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115 | {
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116 | "enum": ["always", "never"]
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117 | }
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118 | ];
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