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 module.exports = {
  82     meta: {
  83         type: "suggestion",
  84
  85         docs: {
  86             description: "disallow unnecessary escape characters",
  87             recommended: true,
  88             url: "https://eslint.org/docs/rules/no-useless-escape"
  89         },
  90
  91         hasSuggestions: true,
  92
  93         messages: {
  94             unnecessaryEscape: "Unnecessary escape character: \\{{character}}.",
  95             removeEscape: "Remove the `\\`. This maintains the current functionality.",
  96             escapeBackslash: "Replace the `\\` with `\\\\` to include the actual backslash character."
  97         },
  98
  99         schema: []
 100     },
 101
 102     create(context) {
 103         const sourceCode = context.getSourceCode();
 104
 105         /**
 106          * Reports a node
 107          * @param {ASTNode} node The node to report
 108          * @param {number} startOffset The backslash's offset from the start of the node
 109          * @param {string} character The uselessly escaped character (not including the backslash)
 110          * @returns {void}
 111          */
 112         function report(node, startOffset, character) {
 113             const rangeStart = node.range[0] + startOffset;
 114             const range = [rangeStart, rangeStart + 1];
 115             const start = sourceCode.getLocFromIndex(rangeStart);
 116
 117             context.report({
 118                 node,
 119                 loc: {
 120                     start,
 121                     end: { line: start.line, column: start.column + 1 }
 122                 },
 123                 messageId: "unnecessaryEscape",
 124                 data: { character },
 125                 suggest: [
 126                     {
 127                         messageId: "removeEscape",
 128                         fix(fixer) {
 129                             return fixer.removeRange(range);
 130                         }
 131                     },
 132                     {
 133                         messageId: "escapeBackslash",
 134                         fix(fixer) {
 135                             return fixer.insertTextBeforeRange(range, "\\");
 136                         }
 137                     }
 138                 ]
 139             });
 140         }
 141
 142         /**
 143          * Checks if the escape character in given string slice is unnecessary.
 144          * @private
 145          * @param {ASTNode} node node to validate.
 146          * @param {string} match string slice to validate.
 147          * @returns {void}
 148          */
 149         function validateString(node, match) {
 150             const isTemplateElement = node.type === "TemplateElement";
 151             const escapedChar = match[0][1];
 152             let isUnnecessaryEscape = !VALID_STRING_ESCAPES.has(escapedChar);
 153             let isQuoteEscape;
 154
 155             if (isTemplateElement) {
 156                 isQuoteEscape = escapedChar === "`";
 157
 158                 if (escapedChar === "$") {
 159
 160                     // Warn if `\$` is not followed by `{`
 161                     isUnnecessaryEscape = match.input[match.index + 2] !== "{";
 162                 } else if (escapedChar === "{") {
 163
 164                     /*
 165                      * Warn if `\{` is not preceded by `$`. If preceded by `$`, escaping
 166                      * is necessary and the rule should not warn. If preceded by `/$`, the rule
 167                      * will warn for the `/$` instead, as it is the first unnecessarily escaped character.
 168                      */
 169                     isUnnecessaryEscape = match.input[match.index - 1] !== "$";
 170                 }
 171             } else {
 172                 isQuoteEscape = escapedChar === node.raw[0];
 173             }
 174
 175             if (isUnnecessaryEscape && !isQuoteEscape) {
 176                 report(node, match.index, match[0].slice(1));
 177             }
 178         }
 179
 180         /**
 181          * Checks if a node has an escape.
 182          * @param {ASTNode} node node to check.
 183          * @returns {void}
 184          */
 185         function check(node) {
 186             const isTemplateElement = node.type === "TemplateElement";
 187
 188             if (
 189                 isTemplateElement &&
 190                 node.parent &&
 191                 node.parent.parent &&
 192                 node.parent.parent.type === "TaggedTemplateExpression" &&
 193                 node.parent === node.parent.parent.quasi
 194             ) {
 195
 196                 // Don't report tagged template literals, because the backslash character is accessible to the tag function.
 197                 return;
 198             }
 199
 200             if (typeof node.value === "string" || isTemplateElement) {
 201
 202                 /*
 203                  * JSXAttribute doesn't have any escape sequence: https://facebook.github.io/jsx/.
 204                  * In addition, backticks are not supported by JSX yet: https://github.com/facebook/jsx/issues/25.
 205                  */
 206                 if (node.parent.type === "JSXAttribute" || node.parent.type === "JSXElement" || node.parent.type === "JSXFragment") {
 207                     return;
 208                 }
 209
 210                 const value = isTemplateElement ? sourceCode.getText(node) : node.raw;
 211                 const pattern = /\\[^\d]/gu;
 212                 let match;
 213
 214                 while ((match = pattern.exec(value))) {
 215                     validateString(node, match);
 216                 }
 217             } else if (node.regex) {
 218                 parseRegExp(node.regex.pattern)
 219
 220                     /*
 221                      * The '-' character is a special case, because it's only valid to escape it if it's in a character
 222                      * class, and is not at either edge of the character class. To account for this, don't consider '-'
 223                      * characters to be valid in general, and filter out '-' characters that appear in the middle of a
 224                      * character class.
 225                      */
 226                     .filter(charInfo => !(charInfo.text === "-" && charInfo.inCharClass && !charInfo.startsCharClass && !charInfo.endsCharClass))
 227
 228                     /*
 229                      * The '^' character is also a special case; it must always be escaped outside of character classes, but
 230                      * it only needs to be escaped in character classes if it's at the beginning of the character class. To
 231                      * account for this, consider it to be a valid escape character outside of character classes, and filter
 232                      * out '^' characters that appear at the start of a character class.
 233                      */
 234                     .filter(charInfo => !(charInfo.text === "^" && charInfo.startsCharClass))
 235
 236                     // Filter out characters that aren't escaped.
 237                     .filter(charInfo => charInfo.escaped)
 238
 239                     // Filter out characters that are valid to escape, based on their position in the regular expression.
 240                     .filter(charInfo => !(charInfo.inCharClass ? REGEX_GENERAL_ESCAPES : REGEX_NON_CHARCLASS_ESCAPES).has(charInfo.text))
 241
 242                     // Report all the remaining characters.
 243                     .forEach(charInfo => report(node, charInfo.index, charInfo.text));
 244             }
 245
 246         }
 247
 248         return {
 249             Literal: check,
 250             TemplateElement: check
 251         };
 252     }
 253 };