/**
* @fileoverview Look for useless escapes in strings and regexes
* @author Onur Temizkan
*/
"use strict";
const astUtils = require("../ast-utils");
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/**
* Returns the union of two sets.
* @param {Set} setA The first set
* @param {Set} setB The second set
* @returns {Set} The union of the two sets
*/
function union(setA, setB) {
return new Set(function *() {
yield* setA;
yield* setB;
}());
}
const VALID_STRING_ESCAPES = union(new Set("\\nrvtbfux"), astUtils.LINEBREAKS);
const REGEX_GENERAL_ESCAPES = new Set("\\bcdDfnrsStvwWxu0123456789]");
const REGEX_NON_CHARCLASS_ESCAPES = union(REGEX_GENERAL_ESCAPES, new Set("^/.$*+?[{}|()B"));
/**
* Parses a regular expression into a list of characters with character class info.
* @param {string} regExpText The raw text used to create the regular expression
* @returns {Object[]} A list of characters, each with info on escaping and whether they're in a character class.
* @example
*
* parseRegExp('a\\b[cd-]')
*
* returns:
* [
* {text: 'a', index: 0, escaped: false, inCharClass: false, startsCharClass: false, endsCharClass: false},
* {text: 'b', index: 2, escaped: true, inCharClass: false, startsCharClass: false, endsCharClass: false},
* {text: 'c', index: 4, escaped: false, inCharClass: true, startsCharClass: true, endsCharClass: false},
* {text: 'd', index: 5, escaped: false, inCharClass: true, startsCharClass: false, endsCharClass: false},
* {text: '-', index: 6, escaped: false, inCharClass: true, startsCharClass: false, endsCharClass: false}
* ]
*/
function parseRegExp(regExpText) {
const charList = [];
regExpText.split("").reduce((state, char, index) => {
if (!state.escapeNextChar) {
if (char === "\\") {
return Object.assign(state, { escapeNextChar: true });
}
if (char === "[" && !state.inCharClass) {
return Object.assign(state, { inCharClass: true, startingCharClass: true });
}
if (char === "]" && state.inCharClass) {
if (charList.length && charList[charList.length - 1].inCharClass) {
charList[charList.length - 1].endsCharClass = true;
}
return Object.assign(state, { inCharClass: false, startingCharClass: false });
}
}
charList.push({
text: char,
index,
escaped: state.escapeNextChar,
inCharClass: state.inCharClass,
startsCharClass: state.startingCharClass,
endsCharClass: false
});
return Object.assign(state, { escapeNextChar: false, startingCharClass: false });
}, { escapeNextChar: false, inCharClass: false, startingCharClass: false });
return charList;
}
module.exports = {
meta: {
docs: {
description: "disallow unnecessary escape characters",
category: "Best Practices",
recommended: true,
url: "https://eslint.org/docs/rules/no-useless-escape"
},
schema: []
},
create(context) {
const sourceCode = context.getSourceCode();
/**
* Reports a node
* @param {ASTNode} node The node to report
* @param {number} startOffset The backslash's offset from the start of the node
* @param {string} character The uselessly escaped character (not including the backslash)
* @returns {void}
*/
function report(node, startOffset, character) {
context.report({
node,
loc: sourceCode.getLocFromIndex(sourceCode.getIndexFromLoc(node.loc.start) + startOffset),
message: "Unnecessary escape character: \\{{character}}.",
data: { character }
});
}
/**
* Checks if the escape character in given string slice is unnecessary.
*
* @private
* @param {ASTNode} node - node to validate.
* @param {string} match - string slice to validate.
* @returns {void}
*/
function validateString(node, match) {
const isTemplateElement = node.type === "TemplateElement";
const escapedChar = match[0][1];
let isUnnecessaryEscape = !VALID_STRING_ESCAPES.has(escapedChar);
let isQuoteEscape;
if (isTemplateElement) {
isQuoteEscape = escapedChar === "`";
if (escapedChar === "$") {
// Warn if `\$` is not followed by `{`
isUnnecessaryEscape = match.input[match.index + 2] !== "{";
} else if (escapedChar === "{") {
/*
* Warn if `\{` is not preceded by `$`. If preceded by `$`, escaping
* is necessary and the rule should not warn. If preceded by `/$`, the rule
* will warn for the `/$` instead, as it is the first unnecessarily escaped character.
*/
isUnnecessaryEscape = match.input[match.index - 1] !== "$";
}
} else {
isQuoteEscape = escapedChar === node.raw[0];
}
if (isUnnecessaryEscape && !isQuoteEscape) {
report(node, match.index + 1, match[0].slice(1));
}
}
/**
* Checks if a node has an escape.
*
* @param {ASTNode} node - node to check.
* @returns {void}
*/
function check(node) {
const isTemplateElement = node.type === "TemplateElement";
if (
isTemplateElement &&
node.parent &&
node.parent.parent &&
node.parent.parent.type === "TaggedTemplateExpression" &&
node.parent === node.parent.parent.quasi
) {
// Don't report tagged template literals, because the backslash character is accessible to the tag function.
return;
}
if (typeof node.value === "string" || isTemplateElement) {
/*
* JSXAttribute doesn't have any escape sequence: https://facebook.github.io/jsx/.
* In addition, backticks are not supported by JSX yet: https://github.com/facebook/jsx/issues/25.
*/
if (node.parent.type === "JSXAttribute" || node.parent.type === "JSXElement") {
return;
}
const value = isTemplateElement ? node.value.raw : node.raw.slice(1, -1);
const pattern = /\\[^\d]/g;
let match;
while ((match = pattern.exec(value))) {
validateString(node, match);
}
} else if (node.regex) {
parseRegExp(node.regex.pattern)
/*
* The '-' character is a special case, because it's only valid to escape it if it's in a character
* class, and is not at either edge of the character class. To account for this, don't consider '-'
* characters to be valid in general, and filter out '-' characters that appear in the middle of a
* character class.
*/
.filter(charInfo => !(charInfo.text === "-" && charInfo.inCharClass && !charInfo.startsCharClass && !charInfo.endsCharClass))
/*
* The '^' character is also a special case; it must always be escaped outside of character classes, but
* it only needs to be escaped in character classes if it's at the beginning of the character class. To
* account for this, consider it to be a valid escape character outside of character classes, and filter
* out '^' characters that appear at the start of a character class.
*/
.filter(charInfo => !(charInfo.text === "^" && charInfo.startsCharClass))
// Filter out characters that aren't escaped.
.filter(charInfo => charInfo.escaped)
// Filter out characters that are valid to escape, based on their position in the regular expression.
.filter(charInfo => !(charInfo.inCharClass ? REGEX_GENERAL_ESCAPES : REGEX_NON_CHARCLASS_ESCAPES).has(charInfo.text))
// Report all the remaining characters.
.forEach(charInfo => report(node, charInfo.index, charInfo.text));
}
}
return {
Literal: check,
TemplateElement: check
};
}
};