1 | /**
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2 | * @fileoverview Rule to flag use of comma operator
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3 | * @author Brandon Mills
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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 | //------------------------------------------------------------------------------
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9 | // Requirements
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10 | //------------------------------------------------------------------------------
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11 |
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12 | const astUtils = require("../ast-utils");
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13 |
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14 | //------------------------------------------------------------------------------
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15 | // Rule Definition
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16 | //------------------------------------------------------------------------------
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17 |
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18 | module.exports = {
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19 | meta: {
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20 | docs: {
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21 | description: "disallow comma operators",
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22 | category: "Best Practices",
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23 | recommended: false,
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24 | url: "https://eslint.org/docs/rules/no-sequences"
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25 | },
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26 |
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27 | schema: []
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28 | },
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29 |
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30 | create(context) {
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31 | const sourceCode = context.getSourceCode();
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32 |
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33 | /**
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34 | * Parts of the grammar that are required to have parens.
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35 | */
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36 | const parenthesized = {
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37 | DoWhileStatement: "test",
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38 | IfStatement: "test",
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39 | SwitchStatement: "discriminant",
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40 | WhileStatement: "test",
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41 | WithStatement: "object",
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42 | ArrowFunctionExpression: "body"
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43 |
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44 | /*
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45 | * Omitting CallExpression - commas are parsed as argument separators
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46 | * Omitting NewExpression - commas are parsed as argument separators
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47 | * Omitting ForInStatement - parts aren't individually parenthesised
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48 | * Omitting ForStatement - parts aren't individually parenthesised
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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 | * Determines whether a node is required by the grammar to be wrapped in
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54 | * parens, e.g. the test of an if statement.
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55 | * @param {ASTNode} node - The AST node
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56 | * @returns {boolean} True if parens around node belong to parent node.
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57 | */
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58 | function requiresExtraParens(node) {
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59 | return node.parent && parenthesized[node.parent.type] &&
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60 | node === node.parent[parenthesized[node.parent.type]];
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61 | }
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62 |
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63 | /**
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64 | * Check if a node is wrapped in parens.
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65 | * @param {ASTNode} node - The AST node
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66 | * @returns {boolean} True if the node has a paren on each side.
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67 | */
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68 | function isParenthesised(node) {
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69 | return astUtils.isParenthesised(sourceCode, node);
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70 | }
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71 |
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72 | /**
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73 | * Check if a node is wrapped in two levels of parens.
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74 | * @param {ASTNode} node - The AST node
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75 | * @returns {boolean} True if two parens surround the node on each side.
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76 | */
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77 | function isParenthesisedTwice(node) {
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78 | const previousToken = sourceCode.getTokenBefore(node, 1),
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79 | nextToken = sourceCode.getTokenAfter(node, 1);
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80 |
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81 | return isParenthesised(node) && previousToken && nextToken &&
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82 | astUtils.isOpeningParenToken(previousToken) && previousToken.range[1] <= node.range[0] &&
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83 | astUtils.isClosingParenToken(nextToken) && nextToken.range[0] >= node.range[1];
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84 | }
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85 |
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86 | return {
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87 | SequenceExpression(node) {
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88 |
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89 | // Always allow sequences in for statement update
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90 | if (node.parent.type === "ForStatement" &&
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91 | (node === node.parent.init || node === node.parent.update)) {
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92 | return;
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93 | }
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94 |
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95 | // Wrapping a sequence in extra parens indicates intent
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96 | if (requiresExtraParens(node)) {
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97 | if (isParenthesisedTwice(node)) {
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98 | return;
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99 | }
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100 | } else {
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101 | if (isParenthesised(node)) {
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102 | return;
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103 | }
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104 | }
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105 |
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106 | const child = sourceCode.getTokenAfter(node.expressions[0]);
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107 |
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108 | context.report({ node, loc: child.loc.start, message: "Unexpected use of comma operator." });
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109 | }
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110 | };
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111 |
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112 | }
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113 | };
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