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no-useless-backreference.js
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no-useless-backreference.js
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/**
* @fileoverview Tests for the no-useless-backreference rule
* @author Milos Djermanovic
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const rule = require("../../../lib/rules/no-useless-backreference");
const RuleTester = require("../../../lib/rule-tester/rule-tester");
//------------------------------------------------------------------------------
// Tests
//------------------------------------------------------------------------------
const ruleTester = new RuleTester({ languageOptions: { ecmaVersion: 2018, sourceType: "script" } });
ruleTester.run("no-useless-backreference", rule, {
valid: [
// not a regular expression
String.raw`'\1(a)'`,
String.raw`regExp('\\1(a)')`,
String.raw`new Regexp('\\1(a)', 'u')`,
String.raw`RegExp.foo('\\1(a)', 'u')`,
String.raw`new foo.RegExp('\\1(a)')`,
// unknown pattern
String.raw`RegExp(p)`,
String.raw`new RegExp(p, 'u')`,
String.raw`RegExp('\\1(a)' + suffix)`,
"new RegExp(`${prefix}\\\\1(a)`)",
// not the global RegExp
String.raw`let RegExp; new RegExp('\\1(a)');`,
String.raw`function foo() { var RegExp; RegExp('\\1(a)', 'u'); }`,
String.raw`function foo(RegExp) { new RegExp('\\1(a)'); }`,
String.raw`if (foo) { const RegExp = bar; RegExp('\\1(a)'); }`,
String.raw`/* globals RegExp:off */ new RegExp('\\1(a)');`,
{
code: String.raw`RegExp('\\1(a)');`,
languageOptions: {
globals: { RegExp: "off" }
}
},
// no capturing groups
String.raw`/(?:)/`,
String.raw`/(?:a)/`,
String.raw`new RegExp('')`,
String.raw`RegExp('(?:a)|(?:b)*')`,
String.raw`/^ab|[cd].\n$/`,
// no backreferences
String.raw`/(a)/`,
String.raw`RegExp('(a)|(b)')`,
String.raw`new RegExp('\\n\\d(a)')`,
String.raw`/\0(a)/`,
String.raw`/\0(a)/u`,
String.raw`/(?<=(a))(b)(?=(c))/`,
String.raw`/(?<!(a))(b)(?!(c))/`,
String.raw`/(?<foo>a)/`,
// not really a backreference
String.raw`RegExp('\1(a)')`, // string octal escape
String.raw`RegExp('\\\\1(a)')`, // escaped backslash
String.raw`/\\1(a)/`, // // escaped backslash
String.raw`/\1/`, // group 1 doesn't exist, this is a regex octal escape
String.raw`/^\1$/`, // group 1 doesn't exist, this is a regex octal escape
String.raw`/\2(a)/`, // group 2 doesn't exist, this is a regex octal escape
String.raw`/\1(?:a)/`, // group 1 doesn't exist, this is a regex octal escape
String.raw`/\1(?=a)/`, // group 1 doesn't exist, this is a regex octal escape
String.raw`/\1(?!a)/`, // group 1 doesn't exist, this is a regex octal escape
String.raw`/^[\1](a)$/`, // \N in a character class is a regex octal escape
String.raw`new RegExp('[\\1](a)')`, // \N in a character class is a regex octal escape
String.raw`/\11(a)/`, // regex octal escape \11, regex matches "\x09a"
String.raw`/\k<foo>(a)/`, // without the 'u' flag and any named groups this isn't a syntax error, matches "k<foo>a"
String.raw`/^(a)\1\2$/`, // \1 is a backreference, \2 is an octal escape sequence.
// Valid backreferences: correct position, after the group
String.raw`/(a)\1/`,
String.raw`/(a).\1/`,
String.raw`RegExp('(a)\\1(b)')`,
String.raw`/(a)(b)\2(c)/`,
String.raw`/(?<foo>a)\k<foo>/`,
String.raw`new RegExp('(.)\\1')`,
String.raw`RegExp('(a)\\1(?:b)')`,
String.raw`/(a)b\1/`,
String.raw`/((a)\2)/`,
String.raw`/((a)b\2c)/`,
String.raw`/^(?:(a)\1)$/`,
String.raw`/^((a)\2)$/`,
String.raw`/^(((a)\3))|b$/`,
String.raw`/a(?<foo>(.)b\2)/`,
String.raw`/(a)?(b)*(\1)(c)/`,
String.raw`/(a)?(b)*(\2)(c)/`,
String.raw`/(?<=(a))b\1/`,
String.raw`/(?<=(?=(a)\1))b/`,
// Valid backreferences: correct position before the group when they're both in the same lookbehind
String.raw`/(?<!\1(a))b/`,
String.raw`/(?<=\1(a))b/`,
String.raw`/(?<!\1.(a))b/`,
String.raw`/(?<=\1.(a))b/`,
String.raw`/(?<=(?:\1.(a)))b/`,
String.raw`/(?<!(?:\1)((a)))b/`,
String.raw`/(?<!(?:\2)((a)))b/`,
String.raw`/(?=(?<=\1(a)))b/`,
String.raw`/(?=(?<!\1(a)))b/`,
String.raw`/(.)(?<=\2(a))b/`,
// Valid backreferences: not a reference into another alternative
String.raw`/^(a)\1|b/`,
String.raw`/^a|(b)\1/`,
String.raw`/^a|(b|c)\1/`,
String.raw`/^(a)|(b)\2/`,
String.raw`/^(?:(a)|(b)\2)$/`,
String.raw`/^a|(?:.|(b)\1)/`,
String.raw`/^a|(?:.|(b).(\1))/`,
String.raw`/^a|(?:.|(?:(b)).(\1))/`,
String.raw`/^a|(?:.|(?:(b)|c).(\1))/`,
String.raw`/^a|(?:.|(?:(b)).(\1|c))/`,
String.raw`/^a|(?:.|(?:(b)|c).(\1|d))/`,
// Valid backreferences: not a reference into a negative lookaround (reference from within the same lookaround is allowed)
String.raw`/.(?=(b))\1/`,
String.raw`/.(?<=(b))\1/`,
String.raw`/a(?!(b)\1)./`,
String.raw`/a(?<!\1(b))./`,
String.raw`/a(?!(b)(\1))./`,
String.raw`/a(?!(?:(b)\1))./`,
String.raw`/a(?!(?:(b))\1)./`,
String.raw`/a(?<!(?:\1)(b))./`,
String.raw`/a(?<!(?:(?:\1)(b)))./`,
String.raw`/(?<!(a))(b)(?!(c))\2/`,
String.raw`/a(?!(b|c)\1)./`,
// ignore regular expressions with syntax errors
String.raw`RegExp('\\1(a)[')`, // \1 would be an error, but the unterminated [ is a syntax error
String.raw`new RegExp('\\1(a){', 'u')`, // \1 would be an error, but the unterminated { is a syntax error because of the 'u' flag
String.raw`new RegExp('\\1(a)\\2', 'ug')`, // \1 would be an error, but \2 is syntax error because of the 'u' flag
String.raw`const flags = 'gus'; RegExp('\\1(a){', flags);`, // \1 would be an error, but the rule is aware of the 'u' flag so this is a syntax error
String.raw`RegExp('\\1(a)\\k<foo>', 'u')`, // \1 would be an error, but \k<foo> produces syntax error because of the u flag
String.raw`new RegExp('\\k<foo>(?<foo>a)\\k<bar>')`, // \k<foo> would be an error, but \k<bar> produces syntax error because group <bar> doesn't exist
// ES2024
String.raw`new RegExp('([[A--B]])\\1', 'v')`,
String.raw`new RegExp('[[]\\1](a)', 'v')` // SyntaxError
],
invalid: [
// full message tests
{
code: String.raw`/(b)(\2a)/`,
errors: [{
message: String.raw`Backreference '\2' will be ignored. It references group '(\2a)' from within that group.`,
type: "Literal"
}]
},
{
code: String.raw`/\k<foo>(?<foo>bar)/`,
errors: [{
message: String.raw`Backreference '\k<foo>' will be ignored. It references group '(?<foo>bar)' which appears later in the pattern.`,
type: "Literal"
}]
},
{
code: String.raw`RegExp('(a|bc)|\\1')`,
errors: [{
message: String.raw`Backreference '\1' will be ignored. It references group '(a|bc)' which is in another alternative.`,
type: "CallExpression"
}]
},
{
code: String.raw`new RegExp('(?!(?<foo>\\n))\\1')`,
errors: [{
message: String.raw`Backreference '\1' will be ignored. It references group '(?<foo>\n)' which is in a negative lookaround.`,
type: "NewExpression"
}]
},
{
code: String.raw`/(?<!(a)\1)b/`,
errors: [{
message: String.raw`Backreference '\1' will be ignored. It references group '(a)' which appears before in the same lookbehind.`,
type: "Literal"
}]
},
// nested
{
code: String.raw`new RegExp('(\\1)')`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(\1)` }, type: "NewExpression" }]
},
{
code: String.raw`/^(a\1)$/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(a\1)` }, type: "Literal" }]
},
{
code: String.raw`/^((a)\1)$/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`((a)\1)` }, type: "Literal" }]
},
{
code: String.raw`new RegExp('^(a\\1b)$')`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(a\1b)` }, type: "NewExpression" }]
},
{
code: String.raw`RegExp('^((\\1))$')`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`((\1))` }, type: "CallExpression" }]
},
{
code: String.raw`/((\2))/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\2`, group: String.raw`(\2)` }, type: "Literal" }]
},
{
code: String.raw`/a(?<foo>(.)b\1)/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(?<foo>(.)b\1)` }, type: "Literal" }]
},
{
code: String.raw`/a(?<foo>\k<foo>)b/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\k<foo>`, group: String.raw`(?<foo>\k<foo>)` }, type: "Literal" }]
},
{
code: String.raw`/^(\1)*$/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(\1)` }, type: "Literal" }]
},
{
code: String.raw`/^(?:a)(?:((?:\1)))*$/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`((?:\1))` }, type: "Literal" }]
},
{
code: String.raw`/(?!(\1))/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(\1)` }, type: "Literal" }]
},
{
code: String.raw`/a|(b\1c)/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(b\1c)` }, type: "Literal" }]
},
{
code: String.raw`/(a|(\1))/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(a|(\1))` }, type: "Literal" }]
},
{
code: String.raw`/(a|(\2))/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\2`, group: String.raw`(\2)` }, type: "Literal" }]
},
{
code: String.raw`/(?:a|(\1))/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(\1)` }, type: "Literal" }]
},
{
code: String.raw`/(a)?(b)*(\3)/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\3`, group: String.raw`(\3)` }, type: "Literal" }]
},
{
code: String.raw`/(?<=(a\1))b/`,
errors: [{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(a\1)` }, type: "Literal" }]
},
// forward
{
code: String.raw`/\1(a)/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/\1.(a)/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?:\1)(?:(a))/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?:\1)(?:((a)))/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`((a))` }, type: "Literal" }]
},
{
code: String.raw`/(?:\2)(?:((a)))/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\2`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?:\1)(?:((?:a)))/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`((?:a))` }, type: "Literal" }]
},
{
code: String.raw`/(\2)(a)/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\2`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`RegExp('(a)\\2(b)')`,
errors: [{ messageId: "forward", data: { bref: String.raw`\2`, group: String.raw`(b)` }, type: "CallExpression" }]
},
{
code: String.raw`/(?:a)(b)\2(c)/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\2`, group: String.raw`(c)` }, type: "Literal" }]
},
{
code: String.raw`/\k<foo>(?<foo>a)/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\k<foo>`, group: String.raw`(?<foo>a)` }, type: "Literal" }]
},
{
code: String.raw`/(?:a(b)\2)(c)/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\2`, group: String.raw`(c)` }, type: "Literal" }]
},
{
code: String.raw`new RegExp('(a)(b)\\3(c)')`,
errors: [{ messageId: "forward", data: { bref: String.raw`\3`, group: String.raw`(c)` }, type: "NewExpression" }]
},
{
code: String.raw`/\1(?<=(a))./`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/\1(?<!(a))./`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<=\1)(?<=(a))/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<!\1)(?<!(a))/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?=\1(a))./`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?!\1(a))./`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
// backward in the same lookbehind
{
code: String.raw`/(?<=(a)\1)b/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<!.(a).\1.)b/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(.)(?<!(b|c)\2)d/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\2`, group: String.raw`(b|c)` }, type: "Literal" }]
},
{
code: String.raw`/(?<=(?:(a)\1))b/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<=(?:(a))\1)b/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<=(a)(?:\1))b/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<!(?:(a))(?:\1))b/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<!(?:(a))(?:\1)|.)b/`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?!(?<!(a)\1))./`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?=(?<!(a)\1))./`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?!(?<=(a)\1))./`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?=(?<=(a)\1))./`,
errors: [{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
// into another alternative
{
code: String.raw`/(a)|\1b/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/^(?:(a)|\1b)$/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/^(?:(a)|b(?:c|\1))$/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/^(?:a|b(?:(c)|\1))$/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(c)` }, type: "Literal" }]
},
{
code: String.raw`/^(?:(a(?!b))|\1b)+$/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a(?!b))` }, type: "Literal" }]
},
{
code: String.raw`/^(?:(?:(a)(?!b))|\1b)+$/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/^(?:(a(?=a))|\1b)+$/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a(?=a))` }, type: "Literal" }]
},
{
code: String.raw`/^(?:(a)(?=a)|\1b)+$/`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?:a|(b)).|(?:(\1)|c)./`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(b)` }, type: "Literal" }]
},
{
code: String.raw`/.(?!(a)|\1)./`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?<=\1|(a))./`,
errors: [{ messageId: "disjunctive", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
// into a negative lookaround
{
code: String.raw`/a(?!(b)).\1/`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(b)` }, type: "Literal" }]
},
{
code: String.raw`/(?<!(a))b\1/`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/(?<!(a))(?:\1)/`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?<!a|(b)).\1/`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(b)` }, type: "Literal" }]
},
{
code: String.raw`/.(?!(a)).(?!\1)./`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?<!(a)).(?<!\1)./`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?=(?!(a))\1)./`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/.(?<!\1(?!(a)))/`,
errors: [{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
// valid and invalid
{
code: String.raw`/\1(a)(b)\2/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
{
code: String.raw`/\1(a)\1/`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }]
},
// multiple invalid
{
code: String.raw`/\1(a)\2(b)/`,
errors: [
{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" },
{ messageId: "forward", data: { bref: String.raw`\2`, group: String.raw`(b)` }, type: "Literal" }
]
},
{
code: String.raw`/\1.(?<=(a)\1)/`,
errors: [
{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" },
{ messageId: "backward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }
]
},
{
code: String.raw`/(?!\1(a)).\1/`,
errors: [
{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" },
{ messageId: "intoNegativeLookaround", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "Literal" }
]
},
{
code: String.raw`/(a)\2(b)/; RegExp('(\\1)');`,
errors: [
{ messageId: "forward", data: { bref: String.raw`\2`, group: String.raw`(b)` }, type: "Literal" },
{ messageId: "nested", data: { bref: String.raw`\1`, group: String.raw`(\1)` }, type: "CallExpression" }
]
},
// when flags cannot be evaluated, it is assumed that the regex doesn't have 'u' flag set, so this will be a correct regex with a useless backreference
{
code: String.raw`RegExp('\\1(a){', flags);`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "CallExpression" }]
},
// able to evaluate some statically known expressions
{
code: String.raw`const r = RegExp, p = '\\1', s = '(a)'; new r(p + s);`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`(a)` }, type: "NewExpression" }]
},
// ES2024
{
code: String.raw`new RegExp('\\1([[A--B]])', 'v')`,
errors: [{ messageId: "forward", data: { bref: String.raw`\1`, group: String.raw`([[A--B]])` }, type: "NewExpression" }]
}
]
});