1 | /**
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2 | * @fileoverview Rule to disallow unused labels.
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3 | * @author Toru Nagashima
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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 | // Rule Definition
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10 | //------------------------------------------------------------------------------
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11 |
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12 | module.exports = {
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13 | meta: {
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14 | type: "suggestion",
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15 |
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16 | docs: {
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17 | description: "disallow unused labels",
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18 | category: "Best Practices",
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19 | recommended: true,
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20 | url: "https://eslint.org/docs/rules/no-unused-labels"
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21 | },
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22 |
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23 | schema: [],
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24 |
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25 | fixable: "code",
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26 |
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27 | messages: {
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28 | unused: "'{{name}}:' is defined but never used."
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29 | }
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30 | },
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31 |
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32 | create(context) {
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33 | const sourceCode = context.getSourceCode();
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34 | let scopeInfo = null;
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35 |
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36 | /**
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37 | * Adds a scope info to the stack.
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38 | * @param {ASTNode} node A node to add. This is a LabeledStatement.
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39 | * @returns {void}
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40 | */
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41 | function enterLabeledScope(node) {
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42 | scopeInfo = {
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43 | label: node.label.name,
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44 | used: false,
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45 | upper: scopeInfo
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46 | };
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47 | }
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48 |
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49 | /**
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50 | * Removes the top of the stack.
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51 | * At the same time, this reports the label if it's never used.
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52 | * @param {ASTNode} node A node to report. This is a LabeledStatement.
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53 | * @returns {void}
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54 | */
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55 | function exitLabeledScope(node) {
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56 | if (!scopeInfo.used) {
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57 | context.report({
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58 | node: node.label,
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59 | messageId: "unused",
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60 | data: node.label,
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61 | fix(fixer) {
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62 |
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63 | /*
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64 | * Only perform a fix if there are no comments between the label and the body. This will be the case
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65 | * when there is exactly one token/comment (the ":") between the label and the body.
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66 | */
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67 | if (sourceCode.getTokenAfter(node.label, { includeComments: true }) ===
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68 | sourceCode.getTokenBefore(node.body, { includeComments: true })) {
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69 | return fixer.removeRange([node.range[0], node.body.range[0]]);
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70 | }
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71 |
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72 | return null;
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73 | }
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74 | });
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75 | }
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76 |
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77 | scopeInfo = scopeInfo.upper;
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78 | }
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79 |
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80 | /**
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81 | * Marks the label of a given node as used.
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82 | * @param {ASTNode} node A node to mark. This is a BreakStatement or
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83 | * ContinueStatement.
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84 | * @returns {void}
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85 | */
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86 | function markAsUsed(node) {
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87 | if (!node.label) {
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88 | return;
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89 | }
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90 |
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91 | const label = node.label.name;
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92 | let info = scopeInfo;
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93 |
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94 | while (info) {
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95 | if (info.label === label) {
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96 | info.used = true;
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97 | break;
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98 | }
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99 | info = info.upper;
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100 | }
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101 | }
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102 |
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103 | return {
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104 | LabeledStatement: enterLabeledScope,
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105 | "LabeledStatement:exit": exitLabeledScope,
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106 | BreakStatement: markAsUsed,
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107 | ContinueStatement: markAsUsed
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108 | };
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109 | }
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110 | };
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