280 lines
11 KiB
JavaScript
280 lines
11 KiB
JavaScript
/**
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* @fileoverview A rule to suggest using template literals instead of string concatenation.
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* @author Toru Nagashima
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Requirements
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//------------------------------------------------------------------------------
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const astUtils = require("./utils/ast-utils");
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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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/**
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* Checks whether or not a given node is a concatenation.
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* @param {ASTNode} node A node to check.
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* @returns {boolean} `true` if the node is a concatenation.
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*/
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function isConcatenation(node) {
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return node.type === "BinaryExpression" && node.operator === "+";
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}
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/**
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* Gets the top binary expression node for concatenation in parents of a given node.
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* @param {ASTNode} node A node to get.
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* @returns {ASTNode} the top binary expression node in parents of a given node.
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*/
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function getTopConcatBinaryExpression(node) {
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let currentNode = node;
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while (isConcatenation(currentNode.parent)) {
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currentNode = currentNode.parent;
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}
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return currentNode;
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}
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/**
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* Determines whether a given node is a octal escape sequence
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* @param {ASTNode} node A node to check
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* @returns {boolean} `true` if the node is an octal escape sequence
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*/
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function isOctalEscapeSequence(node) {
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// No need to check TemplateLiterals – would throw error with octal escape
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const isStringLiteral = node.type === "Literal" && typeof node.value === "string";
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if (!isStringLiteral) {
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return false;
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}
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return astUtils.hasOctalEscapeSequence(node.raw);
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}
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/**
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* Checks whether or not a node contains a octal escape sequence
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* @param {ASTNode} node A node to check
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* @returns {boolean} `true` if the node contains an octal escape sequence
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*/
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function hasOctalEscapeSequence(node) {
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if (isConcatenation(node)) {
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return hasOctalEscapeSequence(node.left) || hasOctalEscapeSequence(node.right);
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}
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return isOctalEscapeSequence(node);
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}
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/**
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* Checks whether or not a given binary expression has string literals.
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* @param {ASTNode} node A node to check.
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* @returns {boolean} `true` if the node has string literals.
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*/
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function hasStringLiteral(node) {
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if (isConcatenation(node)) {
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// `left` is deeper than `right` normally.
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return hasStringLiteral(node.right) || hasStringLiteral(node.left);
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}
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return astUtils.isStringLiteral(node);
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}
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/**
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* Checks whether or not a given binary expression has non string literals.
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* @param {ASTNode} node A node to check.
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* @returns {boolean} `true` if the node has non string literals.
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*/
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function hasNonStringLiteral(node) {
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if (isConcatenation(node)) {
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// `left` is deeper than `right` normally.
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return hasNonStringLiteral(node.right) || hasNonStringLiteral(node.left);
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}
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return !astUtils.isStringLiteral(node);
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}
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/**
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* Determines whether a given node will start with a template curly expression (`${}`) when being converted to a template literal.
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* @param {ASTNode} node The node that will be fixed to a template literal
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* @returns {boolean} `true` if the node will start with a template curly.
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*/
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function startsWithTemplateCurly(node) {
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if (node.type === "BinaryExpression") {
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return startsWithTemplateCurly(node.left);
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}
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if (node.type === "TemplateLiteral") {
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return node.expressions.length && node.quasis.length && node.quasis[0].range[0] === node.quasis[0].range[1];
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}
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return node.type !== "Literal" || typeof node.value !== "string";
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}
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/**
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* Determines whether a given node end with a template curly expression (`${}`) when being converted to a template literal.
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* @param {ASTNode} node The node that will be fixed to a template literal
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* @returns {boolean} `true` if the node will end with a template curly.
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*/
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function endsWithTemplateCurly(node) {
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if (node.type === "BinaryExpression") {
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return startsWithTemplateCurly(node.right);
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}
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if (node.type === "TemplateLiteral") {
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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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}
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return node.type !== "Literal" || typeof node.value !== "string";
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "suggestion",
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docs: {
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description: "require template literals instead of string concatenation",
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category: "ECMAScript 6",
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recommended: false,
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url: "https://eslint.org/docs/rules/prefer-template"
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},
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schema: [],
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fixable: "code"
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},
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create(context) {
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const sourceCode = context.getSourceCode();
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let done = Object.create(null);
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/**
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* Gets the non-token text between two nodes, ignoring any other tokens that appear between the two tokens.
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* @param {ASTNode} node1 The first node
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* @param {ASTNode} node2 The second node
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* @returns {string} The text between the nodes, excluding other tokens
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*/
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function getTextBetween(node1, node2) {
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const allTokens = [node1].concat(sourceCode.getTokensBetween(node1, node2)).concat(node2);
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const sourceText = sourceCode.getText();
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return allTokens.slice(0, -1).reduce((accumulator, token, index) => accumulator + sourceText.slice(token.range[1], allTokens[index + 1].range[0]), "");
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}
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/**
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* Returns a template literal form of the given node.
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* @param {ASTNode} currentNode A node that should be converted to a template literal
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* @param {string} textBeforeNode Text that should appear before the node
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* @param {string} textAfterNode Text that should appear after the node
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* @returns {string} A string form of this node, represented as a template literal
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*/
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function getTemplateLiteral(currentNode, textBeforeNode, textAfterNode) {
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if (currentNode.type === "Literal" && typeof currentNode.value === "string") {
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/*
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* If the current node is a string literal, escape any instances of ${ or ` to prevent them from being interpreted
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* as a template placeholder. However, if the code already contains a backslash before the ${ or `
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* for some reason, don't add another backslash, because that would change the meaning of the code (it would cause
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* an actual backslash character to appear before the dollar sign).
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*/
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return `\`${currentNode.raw.slice(1, -1).replace(/\\*(\$\{|`)/gu, matched => {
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if (matched.lastIndexOf("\\") % 2) {
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return `\\${matched}`;
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}
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return matched;
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// Unescape any quotes that appear in the original Literal that no longer need to be escaped.
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}).replace(new RegExp(`\\\\${currentNode.raw[0]}`, "gu"), currentNode.raw[0])}\``;
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}
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if (currentNode.type === "TemplateLiteral") {
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return sourceCode.getText(currentNode);
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}
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if (isConcatenation(currentNode) && hasStringLiteral(currentNode) && hasNonStringLiteral(currentNode)) {
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const plusSign = sourceCode.getFirstTokenBetween(currentNode.left, currentNode.right, token => token.value === "+");
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const textBeforePlus = getTextBetween(currentNode.left, plusSign);
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const textAfterPlus = getTextBetween(plusSign, currentNode.right);
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const leftEndsWithCurly = endsWithTemplateCurly(currentNode.left);
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const rightStartsWithCurly = startsWithTemplateCurly(currentNode.right);
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if (leftEndsWithCurly) {
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// 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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// `foo${bar}` /* comment */ + 'baz' --> `foo${bar /* comment */ }${baz}`
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return getTemplateLiteral(currentNode.left, textBeforeNode, textBeforePlus + textAfterPlus).slice(0, -1) +
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getTemplateLiteral(currentNode.right, null, textAfterNode).slice(1);
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}
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if (rightStartsWithCurly) {
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// Otherwise, if the right side of the expression starts with a template curly, add the text there.
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// 'foo' /* comment */ + `${bar}baz` --> `foo${ /* comment */ bar}baz`
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return getTemplateLiteral(currentNode.left, textBeforeNode, null).slice(0, -1) +
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getTemplateLiteral(currentNode.right, textBeforePlus + textAfterPlus, textAfterNode).slice(1);
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}
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/*
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* Otherwise, these nodes should not be combined into a template curly, since there is nowhere to put
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* the text between them.
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*/
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return `${getTemplateLiteral(currentNode.left, textBeforeNode, null)}${textBeforePlus}+${textAfterPlus}${getTemplateLiteral(currentNode.right, textAfterNode, null)}`;
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}
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return `\`\${${textBeforeNode || ""}${sourceCode.getText(currentNode)}${textAfterNode || ""}}\``;
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}
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/**
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* Returns a fixer object that converts a non-string binary expression to a template literal
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* @param {SourceCodeFixer} fixer The fixer object
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* @param {ASTNode} node A node that should be converted to a template literal
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* @returns {Object} A fix for this binary expression
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*/
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function fixNonStringBinaryExpression(fixer, node) {
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const topBinaryExpr = getTopConcatBinaryExpression(node.parent);
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if (hasOctalEscapeSequence(topBinaryExpr)) {
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return null;
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}
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return fixer.replaceText(topBinaryExpr, getTemplateLiteral(topBinaryExpr, null, null));
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}
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/**
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* Reports if a given node is string concatenation with non string literals.
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* @param {ASTNode} node A node to check.
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* @returns {void}
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*/
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function checkForStringConcat(node) {
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if (!astUtils.isStringLiteral(node) || !isConcatenation(node.parent)) {
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return;
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}
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const topBinaryExpr = getTopConcatBinaryExpression(node.parent);
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// Checks whether or not this node had been checked already.
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if (done[topBinaryExpr.range[0]]) {
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return;
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}
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done[topBinaryExpr.range[0]] = true;
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if (hasNonStringLiteral(topBinaryExpr)) {
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context.report({
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node: topBinaryExpr,
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message: "Unexpected string concatenation.",
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fix: fixer => fixNonStringBinaryExpression(fixer, node)
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});
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}
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}
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return {
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Program() {
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done = Object.create(null);
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},
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Literal: checkForStringConcat,
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TemplateLiteral: checkForStringConcat
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};
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}
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};
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