116 lines
3.2 KiB
JavaScript
116 lines
3.2 KiB
JavaScript
/**
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* @fileoverview disallow unnecessary concatenation of template strings
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* @author Henry Zhu
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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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* Checks if the given token is a `+` token or not.
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* @param {Token} token The token to check.
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* @returns {boolean} `true` if the token is a `+` token.
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*/
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function isConcatOperatorToken(token) {
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return token.value === "+" && token.type === "Punctuator";
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}
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/**
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* Get's the right most node on the left side of a BinaryExpression with + operator.
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* @param {ASTNode} node A BinaryExpression node to check.
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* @returns {ASTNode} node
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*/
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function getLeft(node) {
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let left = node.left;
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while (isConcatenation(left)) {
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left = left.right;
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}
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return left;
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}
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/**
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* Get's the left most node on the right side of a BinaryExpression with + operator.
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* @param {ASTNode} node A BinaryExpression node to check.
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* @returns {ASTNode} node
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*/
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function getRight(node) {
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let right = node.right;
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while (isConcatenation(right)) {
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right = right.left;
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}
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return right;
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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: "disallow unnecessary concatenation of literals or template literals",
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category: "Best Practices",
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recommended: false,
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url: "https://eslint.org/docs/rules/no-useless-concat"
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},
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schema: [],
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messages: {
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unexpectedConcat: "Unexpected string concatenation of literals."
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}
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},
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create(context) {
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const sourceCode = context.getSourceCode();
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return {
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BinaryExpression(node) {
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// check if not concatenation
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if (node.operator !== "+") {
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return;
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}
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// account for the `foo + "a" + "b"` case
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const left = getLeft(node);
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const right = getRight(node);
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if (astUtils.isStringLiteral(left) &&
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astUtils.isStringLiteral(right) &&
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astUtils.isTokenOnSameLine(left, right)
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) {
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const operatorToken = sourceCode.getFirstTokenBetween(left, right, isConcatOperatorToken);
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context.report({
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node,
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loc: operatorToken.loc,
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messageId: "unexpectedConcat"
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});
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}
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}
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};
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}
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};
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