eslint/lib/rules/no-useless-escape.js

   1 /**
   2  * @fileoverview Look for useless escapes in strings and regexes
   3  * @author Onur Temizkan
   4  */
   5
   6 "use strict";
   7
   8 const astUtils = require("./utils/ast-utils");
   9
  10 //------------------------------------------------------------------------------
  11 // Rule Definition
  12 //------------------------------------------------------------------------------
  13
  14 /**
  15  * Returns the union of two sets.
  16  * @param {Set} setA The first set
  17  * @param {Set} setB The second set
  18  * @returns {Set} The union of the two sets
  19  */
  20 function union(setA, setB) {
  21     return new Set(function *() {
  22         yield* setA;
  23         yield* setB;
  24     }());
  25 }
  26
  27 const VALID_STRING_ESCAPES = union(new Set("\\nrvtbfux"), astUtils.LINEBREAKS);
  28 const REGEX_GENERAL_ESCAPES = new Set("\\bcdDfnpPrsStvwWxu0123456789]");
  29 const REGEX_NON_CHARCLASS_ESCAPES = union(REGEX_GENERAL_ESCAPES, new Set("^/.$*+?[{}|()Bk"));
  30
  31 /**
  32  * Parses a regular expression into a list of characters with character class info.
  33  * @param {string} regExpText The raw text used to create the regular expression
  34  * @returns {Object[]} A list of characters, each with info on escaping and whether they're in a character class.
  35  * @example
  36  *
  37  * parseRegExp("a\\b[cd-]");
  38  *
  39  * // returns:
  40  * [
  41  *     { text: "a", index: 0, escaped: false, inCharClass: false, startsCharClass: false, endsCharClass: false },
  42  *     { text: "b", index: 2, escaped: true, inCharClass: false, startsCharClass: false, endsCharClass: false },
  43  *     { text: "c", index: 4, escaped: false, inCharClass: true, startsCharClass: true, endsCharClass: false },
  44  *     { text: "d", index: 5, escaped: false, inCharClass: true, startsCharClass: false, endsCharClass: false },
  45  *     { text: "-", index: 6, escaped: false, inCharClass: true, startsCharClass: false, endsCharClass: false }
  46  * ];
  47  *
  48  */
  49 function parseRegExp(regExpText) {
  50     const charList = [];
  51
  52     regExpText.split("").reduce((state, char, index) => {
  53         if (!state.escapeNextChar) {
  54             if (char === "\\") {
  55                 return Object.assign(state, { escapeNextChar: true });
  56             }
  57             if (char === "[" && !state.inCharClass) {
  58                 return Object.assign(state, { inCharClass: true, startingCharClass: true });
  59             }
  60             if (char === "]" && state.inCharClass) {
  61                 if (charList.length && charList[charList.length - 1].inCharClass) {
  62                     charList[charList.length - 1].endsCharClass = true;
  63                 }
  64                 return Object.assign(state, { inCharClass: false, startingCharClass: false });
  65             }
  66         }
  67         charList.push({
  68             text: char,
  69             index,
  70             escaped: state.escapeNextChar,
  71             inCharClass: state.inCharClass,
  72             startsCharClass: state.startingCharClass,
  73             endsCharClass: false
  74         });
  75         return Object.assign(state, { escapeNextChar: false, startingCharClass: false });
  76     }, { escapeNextChar: false, inCharClass: false, startingCharClass: false });
  77
  78     return charList;
  79 }
  80
  81 /** @type {import('../shared/types').Rule} */
  82 module.exports = {
  83     meta: {
  84         type: "suggestion",
  85
  86         docs: {
  87             description: "disallow unnecessary escape characters",
  88             recommended: true,
  89             url: "https://eslint.org/docs/rules/no-useless-escape"
  90         },
  91
  92         hasSuggestions: true,
  93
  94         messages: {
  95             unnecessaryEscape: "Unnecessary escape character: \\{{character}}.",
  96             removeEscape: "Remove the `\\`. This maintains the current functionality.",
  97             escapeBackslash: "Replace the `\\` with `\\\\` to include the actual backslash character."
  98         },
  99
 100         schema: []
 101     },
 102
 103     create(context) {
 104         const sourceCode = context.getSourceCode();
 105
 106         /**
 107          * Reports a node
 108          * @param {ASTNode} node The node to report
 109          * @param {number} startOffset The backslash's offset from the start of the node
 110          * @param {string} character The uselessly escaped character (not including the backslash)
 111          * @returns {void}
 112          */
 113         function report(node, startOffset, character) {
 114             const rangeStart = node.range[0] + startOffset;
 115             const range = [rangeStart, rangeStart + 1];
 116             const start = sourceCode.getLocFromIndex(rangeStart);
 117
 118             context.report({
 119                 node,
 120                 loc: {
 121                     start,
 122                     end: { line: start.line, column: start.column + 1 }
 123                 },
 124                 messageId: "unnecessaryEscape",
 125                 data: { character },
 126                 suggest: [
 127                     {
 128                         messageId: "removeEscape",
 129                         fix(fixer) {
 130                             return fixer.removeRange(range);
 131                         }
 132                     },
 133                     {
 134                         messageId: "escapeBackslash",
 135                         fix(fixer) {
 136                             return fixer.insertTextBeforeRange(range, "\\");
 137                         }
 138                     }
 139                 ]
 140             });
 141         }
 142
 143         /**
 144          * Checks if the escape character in given string slice is unnecessary.
 145          * @private
 146          * @param {ASTNode} node node to validate.
 147          * @param {string} match string slice to validate.
 148          * @returns {void}
 149          */
 150         function validateString(node, match) {
 151             const isTemplateElement = node.type === "TemplateElement";
 152             const escapedChar = match[0][1];
 153             let isUnnecessaryEscape = !VALID_STRING_ESCAPES.has(escapedChar);
 154             let isQuoteEscape;
 155
 156             if (isTemplateElement) {
 157                 isQuoteEscape = escapedChar === "`";
 158
 159                 if (escapedChar === "$") {
 160
 161                     // Warn if `\$` is not followed by `{`
 162                     isUnnecessaryEscape = match.input[match.index + 2] !== "{";
 163                 } else if (escapedChar === "{") {
 164
 165                     /*
 166                      * Warn if `\{` is not preceded by `$`. If preceded by `$`, escaping
 167                      * is necessary and the rule should not warn. If preceded by `/$`, the rule
 168                      * will warn for the `/$` instead, as it is the first unnecessarily escaped character.
 169                      */
 170                     isUnnecessaryEscape = match.input[match.index - 1] !== "$";
 171                 }
 172             } else {
 173                 isQuoteEscape = escapedChar === node.raw[0];
 174             }
 175
 176             if (isUnnecessaryEscape && !isQuoteEscape) {
 177                 report(node, match.index, match[0].slice(1));
 178             }
 179         }
 180
 181         /**
 182          * Checks if a node has an escape.
 183          * @param {ASTNode} node node to check.
 184          * @returns {void}
 185          */
 186         function check(node) {
 187             const isTemplateElement = node.type === "TemplateElement";
 188
 189             if (
 190                 isTemplateElement &&
 191                 node.parent &&
 192                 node.parent.parent &&
 193                 node.parent.parent.type === "TaggedTemplateExpression" &&
 194                 node.parent === node.parent.parent.quasi
 195             ) {
 196
 197                 // Don't report tagged template literals, because the backslash character is accessible to the tag function.
 198                 return;
 199             }
 200
 201             if (typeof node.value === "string" || isTemplateElement) {
 202
 203                 /*
 204                  * JSXAttribute doesn't have any escape sequence: https://facebook.github.io/jsx/.
 205                  * In addition, backticks are not supported by JSX yet: https://github.com/facebook/jsx/issues/25.
 206                  */
 207                 if (node.parent.type === "JSXAttribute" || node.parent.type === "JSXElement" || node.parent.type === "JSXFragment") {
 208                     return;
 209                 }
 210
 211                 const value = isTemplateElement ? sourceCode.getText(node) : node.raw;
 212                 const pattern = /\\[^\d]/gu;
 213                 let match;
 214
 215                 while ((match = pattern.exec(value))) {
 216                     validateString(node, match);
 217                 }
 218             } else if (node.regex) {
 219                 parseRegExp(node.regex.pattern)
 220
 221                     /*
 222                      * The '-' character is a special case, because it's only valid to escape it if it's in a character
 223                      * class, and is not at either edge of the character class. To account for this, don't consider '-'
 224                      * characters to be valid in general, and filter out '-' characters that appear in the middle of a
 225                      * character class.
 226                      */
 227                     .filter(charInfo => !(charInfo.text === "-" && charInfo.inCharClass && !charInfo.startsCharClass && !charInfo.endsCharClass))
 228
 229                     /*
 230                      * The '^' character is also a special case; it must always be escaped outside of character classes, but
 231                      * it only needs to be escaped in character classes if it's at the beginning of the character class. To
 232                      * account for this, consider it to be a valid escape character outside of character classes, and filter
 233                      * out '^' characters that appear at the start of a character class.
 234                      */
 235                     .filter(charInfo => !(charInfo.text === "^" && charInfo.startsCharClass))
 236
 237                     // Filter out characters that aren't escaped.
 238                     .filter(charInfo => charInfo.escaped)
 239
 240                     // Filter out characters that are valid to escape, based on their position in the regular expression.
 241                     .filter(charInfo => !(charInfo.inCharClass ? REGEX_GENERAL_ESCAPES : REGEX_NON_CHARCLASS_ESCAPES).has(charInfo.text))
 242
 243                     // Report all the remaining characters.
 244                     .forEach(charInfo => report(node, charInfo.index, charInfo.text));
 245             }
 246
 247         }
 248
 249         return {
 250             Literal: check,
 251             TemplateElement: check
 252         };
 253     }
 254 };