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