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1/**
2 * @fileoverview Rule to disallow unused labels.
3 * @author Toru Nagashima
4 */
5
6"use strict";
7
8//------------------------------------------------------------------------------
9// Rule Definition
10//------------------------------------------------------------------------------
11
12module.exports = {
13    meta: {
14        type: "suggestion",
15
16        docs: {
17            description: "disallow unused labels",
18            category: "Best Practices",
19            recommended: true,
20            url: "https://eslint.org/docs/rules/no-unused-labels"
21        },
22
23        schema: [],
24
25        fixable: "code",
26
27        messages: {
28            unused: "'{{name}}:' is defined but never used."
29        }
30    },
31
32    create(context) {
33        const sourceCode = context.getSourceCode();
34        let scopeInfo = null;
35
36        /**
37         * Adds a scope info to the stack.
38         * @param {ASTNode} node A node to add. This is a LabeledStatement.
39         * @returns {void}
40         */
41        function enterLabeledScope(node) {
42            scopeInfo = {
43                label: node.label.name,
44                used: false,
45                upper: scopeInfo
46            };
47        }
48
49        /**
50         * Removes the top of the stack.
51         * At the same time, this reports the label if it's never used.
52         * @param {ASTNode} node A node to report. This is a LabeledStatement.
53         * @returns {void}
54         */
55        function exitLabeledScope(node) {
56            if (!scopeInfo.used) {
57                context.report({
58                    node: node.label,
59                    messageId: "unused",
60                    data: node.label,
61                    fix(fixer) {
62
63                        /*
64                         * Only perform a fix if there are no comments between the label and the body. This will be the case
65                         * when there is exactly one token/comment (the ":") between the label and the body.
66                         */
67                        if (sourceCode.getTokenAfter(node.label, { includeComments: true }) ===
68                                sourceCode.getTokenBefore(node.body, { includeComments: true })) {
69                            return fixer.removeRange([node.range[0], node.body.range[0]]);
70                        }
71
72                        return null;
73                    }
74                });
75            }
76
77            scopeInfo = scopeInfo.upper;
78        }
79
80        /**
81         * Marks the label of a given node as used.
82         * @param {ASTNode} node A node to mark. This is a BreakStatement or
83         *      ContinueStatement.
84         * @returns {void}
85         */
86        function markAsUsed(node) {
87            if (!node.label) {
88                return;
89            }
90
91            const label = node.label.name;
92            let info = scopeInfo;
93
94            while (info) {
95                if (info.label === label) {
96                    info.used = true;
97                    break;
98                }
99                info = info.upper;
100            }
101        }
102
103        return {
104            LabeledStatement: enterLabeledScope,
105            "LabeledStatement:exit": exitLabeledScope,
106            BreakStatement: markAsUsed,
107            ContinueStatement: markAsUsed
108        };
109    }
110};
111