@linaria/postcss-linaria: stylelint --fix repeatedly doubles existing backslashes

[aki05162525]

Environment

• @linaria/postcss-linaria: 8.1.1
• Stylelint: 17.14.1
• PostCSS: 8.5.23
• Node.js: 24.16.0
• OS: macOS

Description

Running stylelint --fix with customSyntax: '@linaria/postcss-linaria' doubles
existing backslashes inside Linaria CSS templates.

For example:

- content: '\u2022';
+ content: '\\u2022';

This reproduces with zero Stylelint rules configured, so the corruption occurs during
the @linaria/postcss-linaria parse/stringify round trip rather than in a rule fixer.

The change is also non-idempotent. Each subsequent run doubles the backslashes again:

\u2022 → \\u2022 → \\\\u2022

Reproduction

.stylelintrc.mjs:

export default {
  customSyntax: '@linaria/postcss-linaria',
  rules: {},
};

sample.style.ts:

import { css } from '@linaria/core';

export const style = css`
  .foo {
    &:before {
      content: '\u2022';
      color: red;
    }
  }
`;

Run:

stylelint --config .stylelintrc.mjs --fix sample.style.ts

Expected:

content: '\u2022';

Actual:

content: '\\u2022';

Running the same command again changes it to:

content: '\\\\u2022';

Likely cause

LinariaStringifier unconditionally doubles backslashes for every non-root node:

builder(str.replace(/\\/g, '\\\\').replace(/`/g, '\\`'), node, type);

This also runs on unchanged declaration values, so existing backslashes are escaped
again each time the file is stringified.