1 | /**
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2 | * @fileoverview A rule to suggest using template literals instead of string concatenation.
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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 | // 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 | // Helpers
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16 | //------------------------------------------------------------------------------
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17 |
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18 | /**
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19 | * Checks whether or not a given node is a concatenation.
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20 | * @param {ASTNode} node - A node to check.
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21 | * @returns {boolean} `true` if the node is a concatenation.
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22 | */
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23 | function isConcatenation(node) {
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24 | return node.type === "BinaryExpression" && node.operator === "+";
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25 | }
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26 |
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27 | /**
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28 | * Gets the top binary expression node for concatenation in parents of a given node.
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29 | * @param {ASTNode} node - A node to get.
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30 | * @returns {ASTNode} the top binary expression node in parents of a given node.
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31 | */
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32 | function getTopConcatBinaryExpression(node) {
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33 | while (isConcatenation(node.parent)) {
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34 | node = node.parent;
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35 | }
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36 | return node;
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37 | }
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38 |
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39 | /**
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40 | * Checks whether or not a given binary expression has string literals.
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41 | * @param {ASTNode} node - A node to check.
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42 | * @returns {boolean} `true` if the node has string literals.
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43 | */
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44 | function hasStringLiteral(node) {
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45 | if (isConcatenation(node)) {
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46 |
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47 | // `left` is deeper than `right` normally.
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48 | return hasStringLiteral(node.right) || hasStringLiteral(node.left);
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49 | }
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50 | return astUtils.isStringLiteral(node);
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51 | }
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52 |
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53 | /**
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54 | * Checks whether or not a given binary expression has non string literals.
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55 | * @param {ASTNode} node - A node to check.
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56 | * @returns {boolean} `true` if the node has non string literals.
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57 | */
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58 | function hasNonStringLiteral(node) {
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59 | if (isConcatenation(node)) {
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60 |
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61 | // `left` is deeper than `right` normally.
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62 | return hasNonStringLiteral(node.right) || hasNonStringLiteral(node.left);
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63 | }
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64 | return !astUtils.isStringLiteral(node);
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65 | }
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66 |
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67 | /**
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68 | * Determines whether a given node will start with a template curly expression (`${}`) when being converted to a template literal.
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69 | * @param {ASTNode} node The node that will be fixed to a template literal
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70 | * @returns {boolean} `true` if the node will start with a template curly.
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71 | */
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72 | function startsWithTemplateCurly(node) {
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73 | if (node.type === "BinaryExpression") {
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74 | return startsWithTemplateCurly(node.left);
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75 | }
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76 | if (node.type === "TemplateLiteral") {
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77 | return node.expressions.length && node.quasis.length && node.quasis[0].range[0] === node.quasis[0].range[1];
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78 | }
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79 | return node.type !== "Literal" || typeof node.value !== "string";
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80 | }
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81 |
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82 | /**
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83 | * Determines whether a given node end with a template curly expression (`${}`) when being converted to a template literal.
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84 | * @param {ASTNode} node The node that will be fixed to a template literal
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85 | * @returns {boolean} `true` if the node will end with a template curly.
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86 | */
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87 | function endsWithTemplateCurly(node) {
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88 | if (node.type === "BinaryExpression") {
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89 | return startsWithTemplateCurly(node.right);
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90 | }
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91 | if (node.type === "TemplateLiteral") {
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92 | return node.expressions.length && node.quasis.length && node.quasis[node.quasis.length - 1].range[0] === node.quasis[node.quasis.length - 1].range[1];
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93 | }
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94 | return node.type !== "Literal" || typeof node.value !== "string";
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95 | }
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96 |
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97 | //------------------------------------------------------------------------------
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98 | // Rule Definition
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99 | //------------------------------------------------------------------------------
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100 |
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101 | module.exports = {
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102 | meta: {
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103 | docs: {
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104 | description: "require template literals instead of string concatenation",
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105 | category: "ECMAScript 6",
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106 | recommended: false,
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107 | url: "https://eslint.org/docs/rules/prefer-template"
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108 | },
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109 |
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110 | schema: [],
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111 |
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112 | fixable: "code"
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113 | },
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114 |
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115 | create(context) {
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116 | const sourceCode = context.getSourceCode();
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117 | let done = Object.create(null);
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118 |
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119 | /**
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120 | * Gets the non-token text between two nodes, ignoring any other tokens that appear between the two tokens.
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121 | * @param {ASTNode} node1 The first node
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122 | * @param {ASTNode} node2 The second node
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123 | * @returns {string} The text between the nodes, excluding other tokens
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124 | */
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125 | function getTextBetween(node1, node2) {
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126 | const allTokens = [node1].concat(sourceCode.getTokensBetween(node1, node2)).concat(node2);
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127 | const sourceText = sourceCode.getText();
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128 |
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129 | return allTokens.slice(0, -1).reduce((accumulator, token, index) => accumulator + sourceText.slice(token.range[1], allTokens[index + 1].range[0]), "");
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130 | }
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131 |
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132 | /**
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133 | * Returns a template literal form of the given node.
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134 | * @param {ASTNode} currentNode A node that should be converted to a template literal
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135 | * @param {string} textBeforeNode Text that should appear before the node
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136 | * @param {string} textAfterNode Text that should appear after the node
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137 | * @returns {string} A string form of this node, represented as a template literal
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138 | */
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139 | function getTemplateLiteral(currentNode, textBeforeNode, textAfterNode) {
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140 | if (currentNode.type === "Literal" && typeof currentNode.value === "string") {
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141 |
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142 | /*
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143 | * If the current node is a string literal, escape any instances of ${ or ` to prevent them from being interpreted
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144 | * as a template placeholder. However, if the code already contains a backslash before the ${ or `
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145 | * for some reason, don't add another backslash, because that would change the meaning of the code (it would cause
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146 | * an actual backslash character to appear before the dollar sign).
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147 | */
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148 | return `\`${currentNode.raw.slice(1, -1).replace(/\\*(\${|`)/g, matched => {
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149 | if (matched.lastIndexOf("\\") % 2) {
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150 | return `\\${matched}`;
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151 | }
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152 | return matched;
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153 |
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154 | // Unescape any quotes that appear in the original Literal that no longer need to be escaped.
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155 | }).replace(new RegExp(`\\\\${currentNode.raw[0]}`, "g"), currentNode.raw[0])}\``;
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156 | }
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157 |
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158 | if (currentNode.type === "TemplateLiteral") {
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159 | return sourceCode.getText(currentNode);
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160 | }
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161 |
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162 | if (isConcatenation(currentNode) && hasStringLiteral(currentNode) && hasNonStringLiteral(currentNode)) {
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163 | const plusSign = sourceCode.getFirstTokenBetween(currentNode.left, currentNode.right, token => token.value === "+");
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164 | const textBeforePlus = getTextBetween(currentNode.left, plusSign);
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165 | const textAfterPlus = getTextBetween(plusSign, currentNode.right);
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166 | const leftEndsWithCurly = endsWithTemplateCurly(currentNode.left);
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167 | const rightStartsWithCurly = startsWithTemplateCurly(currentNode.right);
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168 |
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169 | if (leftEndsWithCurly) {
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170 |
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171 | // If the left side of the expression ends with a template curly, add the extra text to the end of the curly bracket.
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172 | // `foo${bar}` /* comment */ + 'baz' --> `foo${bar /* comment */ }${baz}`
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173 | return getTemplateLiteral(currentNode.left, textBeforeNode, textBeforePlus + textAfterPlus).slice(0, -1) +
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174 | getTemplateLiteral(currentNode.right, null, textAfterNode).slice(1);
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175 | }
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176 | if (rightStartsWithCurly) {
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177 |
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178 | // Otherwise, if the right side of the expression starts with a template curly, add the text there.
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179 | // 'foo' /* comment */ + `${bar}baz` --> `foo${ /* comment */ bar}baz`
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180 | return getTemplateLiteral(currentNode.left, textBeforeNode, null).slice(0, -1) +
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181 | getTemplateLiteral(currentNode.right, textBeforePlus + textAfterPlus, textAfterNode).slice(1);
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182 | }
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183 |
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184 | /*
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185 | * Otherwise, these nodes should not be combined into a template curly, since there is nowhere to put
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186 | * the text between them.
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187 | */
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188 | return `${getTemplateLiteral(currentNode.left, textBeforeNode, null)}${textBeforePlus}+${textAfterPlus}${getTemplateLiteral(currentNode.right, textAfterNode, null)}`;
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189 | }
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190 |
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191 | return `\`\${${textBeforeNode || ""}${sourceCode.getText(currentNode)}${textAfterNode || ""}}\``;
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192 | }
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193 |
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194 | /**
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195 | * Reports if a given node is string concatenation with non string literals.
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196 | *
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197 | * @param {ASTNode} node - A node to check.
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198 | * @returns {void}
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199 | */
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200 | function checkForStringConcat(node) {
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201 | if (!astUtils.isStringLiteral(node) || !isConcatenation(node.parent)) {
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202 | return;
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203 | }
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204 |
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205 | const topBinaryExpr = getTopConcatBinaryExpression(node.parent);
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206 |
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207 | // Checks whether or not this node had been checked already.
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208 | if (done[topBinaryExpr.range[0]]) {
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209 | return;
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210 | }
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211 | done[topBinaryExpr.range[0]] = true;
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212 |
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213 | if (hasNonStringLiteral(topBinaryExpr)) {
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214 | context.report({
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215 | node: topBinaryExpr,
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216 | message: "Unexpected string concatenation.",
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217 | fix(fixer) {
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218 | return fixer.replaceText(topBinaryExpr, getTemplateLiteral(topBinaryExpr, null, null));
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219 | }
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220 | });
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221 | }
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222 | }
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223 |
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224 | return {
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225 | Program() {
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226 | done = Object.create(null);
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227 | },
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228 |
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229 | Literal: checkForStringConcat,
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230 | TemplateLiteral: checkForStringConcat
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231 | };
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232 | }
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233 | };
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