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1/**
2 * @fileoverview Restrict usage of duplicate imports.
3 * @author Simen Bekkhus
4 */
5"use strict";
6
7//------------------------------------------------------------------------------
8// Rule Definition
9//------------------------------------------------------------------------------
10
11/**
12 * Returns the name of the module imported or re-exported.
13 * @param {ASTNode} node A node to get.
14 * @returns {string} the name of the module, or empty string if no name.
15 */
16function getValue(node) {
17    if (node && node.source && node.source.value) {
18        return node.source.value.trim();
19    }
20
21    return "";
22}
23
24/**
25 * Checks if the name of the import or export exists in the given array, and reports if so.
26 * @param {RuleContext} context The ESLint rule context object.
27 * @param {ASTNode} node A node to get.
28 * @param {string} value The name of the imported or exported module.
29 * @param {string[]} array The array containing other imports or exports in the file.
30 * @param {string} messageId A messageId to be reported after the name of the module
31 *
32 * @returns {void} No return value
33 */
34function checkAndReport(context, node, value, array, messageId) {
35    if (array.indexOf(value) !== -1) {
36        context.report({
37            node,
38            messageId,
39            data: {
40                module: value
41            }
42        });
43    }
44}
45
46/**
47 * @callback nodeCallback
48 * @param {ASTNode} node A node to handle.
49 */
50
51/**
52 * Returns a function handling the imports of a given file
53 * @param {RuleContext} context The ESLint rule context object.
54 * @param {boolean} includeExports Whether or not to check for exports in addition to imports.
55 * @param {string[]} importsInFile The array containing other imports in the file.
56 * @param {string[]} exportsInFile The array containing other exports in the file.
57 *
58 * @returns {nodeCallback} A function passed to ESLint to handle the statement.
59 */
60function handleImports(context, includeExports, importsInFile, exportsInFile) {
61    return function(node) {
62        const value = getValue(node);
63
64        if (value) {
65            checkAndReport(context, node, value, importsInFile, "import");
66
67            if (includeExports) {
68                checkAndReport(context, node, value, exportsInFile, "importAs");
69            }
70
71            importsInFile.push(value);
72        }
73    };
74}
75
76/**
77 * Returns a function handling the exports of a given file
78 * @param {RuleContext} context The ESLint rule context object.
79 * @param {string[]} importsInFile The array containing other imports in the file.
80 * @param {string[]} exportsInFile The array containing other exports in the file.
81 *
82 * @returns {nodeCallback} A function passed to ESLint to handle the statement.
83 */
84function handleExports(context, importsInFile, exportsInFile) {
85    return function(node) {
86        const value = getValue(node);
87
88        if (value) {
89            checkAndReport(context, node, value, exportsInFile, "export");
90            checkAndReport(context, node, value, importsInFile, "exportAs");
91
92            exportsInFile.push(value);
93        }
94    };
95}
96
97module.exports = {
98    meta: {
99        type: "problem",
100
101        docs: {
102            description: "disallow duplicate module imports",
103            category: "ECMAScript 6",
104            recommended: false,
105            url: "https://eslint.org/docs/rules/no-duplicate-imports"
106        },
107
108        schema: [{
109            type: "object",
110            properties: {
111                includeExports: {
112                    type: "boolean",
113                    default: false
114                }
115            },
116            additionalProperties: false
117        }],
118        messages: {
119            import: "'{{module}}' import is duplicated.",
120            importAs: "'{{module}}' import is duplicated as export.",
121            export: "'{{module}}' export is duplicated.",
122            exportAs: "'{{module}}' export is duplicated as import."
123        }
124    },
125
126    create(context) {
127        const includeExports = (context.options[0] || {}).includeExports,
128            importsInFile = [],
129            exportsInFile = [];
130
131        const handlers = {
132            ImportDeclaration: handleImports(context, includeExports, importsInFile, exportsInFile)
133        };
134
135        if (includeExports) {
136            handlers.ExportNamedDeclaration = handleExports(context, importsInFile, exportsInFile);
137            handlers.ExportAllDeclaration = handleExports(context, importsInFile, exportsInFile);
138        }
139
140        return handlers;
141    }
142};
143