1 | /**
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2 | * @fileoverview Rule to flag use of unary increment and decrement operators.
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3 | * @author Ian Christian Myers
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4 | * @author Brody McKee (github.com/mrmckeb)
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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 | //------------------------------------------------------------------------------
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10 | // Helpers
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11 | //------------------------------------------------------------------------------
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12 |
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13 | /**
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14 | * Determines whether the given node is the update node of a `ForStatement`.
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15 | * @param {ASTNode} node The node to check.
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16 | * @returns {boolean} `true` if the node is `ForStatement` update.
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17 | */
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18 | function isForStatementUpdate(node) {
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19 | const parent = node.parent;
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20 |
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21 | return parent.type === "ForStatement" && parent.update === node;
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22 | }
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23 |
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24 | /**
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25 | * Determines whether the given node is considered to be a for loop "afterthought" by the logic of this rule.
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26 | * In particular, it returns `true` if the given node is either:
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27 | * - The update node of a `ForStatement`: for (;; i++) {}
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28 | * - An operand of a sequence expression that is the update node: for (;; foo(), i++) {}
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29 | * - An operand of a sequence expression that is child of another sequence expression, etc.,
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30 | * up to the sequence expression that is the update node: for (;; foo(), (bar(), (baz(), i++))) {}
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31 | * @param {ASTNode} node The node to check.
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32 | * @returns {boolean} `true` if the node is a for loop afterthought.
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33 | */
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34 | function isForLoopAfterthought(node) {
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35 | const parent = node.parent;
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36 |
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37 | if (parent.type === "SequenceExpression") {
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38 | return isForLoopAfterthought(parent);
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39 | }
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40 |
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41 | return isForStatementUpdate(node);
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42 | }
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43 |
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44 | //------------------------------------------------------------------------------
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45 | // Rule Definition
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46 | //------------------------------------------------------------------------------
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47 |
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48 | module.exports = {
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49 | meta: {
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50 | type: "suggestion",
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51 |
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52 | docs: {
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53 | description: "disallow the unary operators `++` and `--`",
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54 | category: "Stylistic Issues",
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55 | recommended: false,
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56 | url: "https://eslint.org/docs/rules/no-plusplus"
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57 | },
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58 |
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59 | schema: [
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60 | {
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61 | type: "object",
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62 | properties: {
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63 | allowForLoopAfterthoughts: {
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64 | type: "boolean",
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65 | default: false
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66 | }
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67 | },
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68 | additionalProperties: false
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69 | }
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70 | ],
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71 |
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72 | messages: {
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73 | unexpectedUnaryOp: "Unary operator '{{operator}}' used."
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74 | }
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75 | },
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76 |
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77 | create(context) {
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78 |
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79 | const config = context.options[0];
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80 | let allowForLoopAfterthoughts = false;
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81 |
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82 | if (typeof config === "object") {
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83 | allowForLoopAfterthoughts = config.allowForLoopAfterthoughts === true;
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84 | }
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85 |
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86 | return {
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87 |
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88 | UpdateExpression(node) {
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89 | if (allowForLoopAfterthoughts && isForLoopAfterthought(node)) {
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90 | return;
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91 | }
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92 |
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93 | context.report({
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94 | node,
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95 | messageId: "unexpectedUnaryOp",
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96 | data: {
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97 | operator: node.operator
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98 | }
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99 | });
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100 | }
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101 |
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102 | };
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103 |
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104 | }
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105 | };
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