eslint/lib/rules/no-nonoctal-decimal-escape.js

/**
 * @fileoverview Rule to disallow `\8` and `\9` escape sequences in string literals.
 * @author Milos Djermanovic
 */

"use strict";

//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------

const QUICK_TEST_REGEX = /\\[89]/u;

/**
 * Returns unicode escape sequence that represents the given character.
 * @param {string} character A single code unit.
 * @returns {string} "\uXXXX" sequence.
 */
function getUnicodeEscape(character) {
    return `\\u${character.charCodeAt(0).toString(16).padStart(4, "0")}`;
}

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

module.exports = {
    meta: {
        type: "suggestion",

        docs: {
            description: "disallow `\\8` and `\\9` escape sequences in string literals",
            category: "Best Practices",
            recommended: false,
            url: "https://eslint.org/docs/rules/no-nonoctal-decimal-escape",
            suggestion: true
        },

        schema: [],

        messages: {
            decimalEscape: "Don't use '{{decimalEscape}}' escape sequence.",

            // suggestions
            refactor: "Replace '{{original}}' with '{{replacement}}'. This maintains the current functionality.",
            escapeBackslash: "Replace '{{original}}' with '{{replacement}}' to include the actual backslash character."
        }
    },

    create(context) {
        const sourceCode = context.getSourceCode();

        /**
         * Creates a new Suggestion object.
         * @param {string} messageId "refactor" or "escapeBackslash".
         * @param {int[]} range The range to replace.
         * @param {string} replacement New text for the range.
         * @returns {Object} Suggestion
         */
        function createSuggestion(messageId, range, replacement) {
            return {
                messageId,
                data: {
                    original: sourceCode.getText().slice(...range),
                    replacement
                },
                fix(fixer) {
                    return fixer.replaceTextRange(range, replacement);
                }
            };
        }

        return {
            Literal(node) {
                if (typeof node.value !== "string") {
                    return;
                }

                if (!QUICK_TEST_REGEX.test(node.raw)) {
                    return;
                }

                const regex = /(?:[^\\]|(?<previousEscape>\\.))*?(?<decimalEscape>\\[89])/suy;
                let match;

                while ((match = regex.exec(node.raw))) {
                    const { previousEscape, decimalEscape } = match.groups;
                    const decimalEscapeRangeEnd = node.range[0] + match.index + match[0].length;
                    const decimalEscapeRangeStart = decimalEscapeRangeEnd - decimalEscape.length;
                    const decimalEscapeRange = [decimalEscapeRangeStart, decimalEscapeRangeEnd];
                    const suggest = [];

                    // When `regex` is matched, `previousEscape` can only capture characters adjacent to `decimalEscape`
                    if (previousEscape === "\\0") {

                        /*
                         * Now we have a NULL escape "\0" immediately followed by a decimal escape, e.g.: "\0\8".
                         * Fixing this to "\08" would turn "\0" into a legacy octal escape. To avoid producing
                         * an octal escape while fixing a decimal escape, we provide different suggestions.
                         */
                        suggest.push(
                            createSuggestion( // "\0\8" -> "\u00008"
                                "refactor",
                                [decimalEscapeRangeStart - previousEscape.length, decimalEscapeRangeEnd],
                                `${getUnicodeEscape("\0")}${decimalEscape[1]}`
                            ),
                            createSuggestion( // "\8" -> "\u0038"
                                "refactor",
                                decimalEscapeRange,
                                getUnicodeEscape(decimalEscape[1])
                            )
                        );
                    } else {
                        suggest.push(
                            createSuggestion( // "\8" -> "8"
                                "refactor",
                                decimalEscapeRange,
                                decimalEscape[1]
                            )
                        );
                    }

                    suggest.push(
                        createSuggestion( // "\8" -> "\\8"
                            "escapeBackslash",
                            decimalEscapeRange,
                            `\\${decimalEscape}`
                        )
                    );

                    context.report({
                        node,
                        loc: {
                            start: sourceCode.getLocFromIndex(decimalEscapeRangeStart),
                            end: sourceCode.getLocFromIndex(decimalEscapeRangeEnd)
                        },
                        messageId: "decimalEscape",
                        data: {
                            decimalEscape
                        },
                        suggest
                    });
                }
            }
        };
    }
};