"Unterminated nested statement!" using TYPO3 rector

TYPO3 rector is a really helpful application when it comes to TYPO3 major updates. It helps you to identify and refactor TYPO3 deprecations in custom extensions and can save hours of manual refactoring. I use TYPO3 rector quite a lot and stumbled across the following error recently.

This message is not really helpful, so I digged deeper into the problem. The Parser.php throwing the exception is located in helmich/typo3-typoscript-parser package, so I first thought that there was a problem with the TypoScript in the desired extension, but after checking ever line manually, I could not find any error.

It came out, that the extension I wanted to process by TYPO3 rector had a node_modules folder, which contained a lot of Typescript (not TypoScript) files. Those files where obviously parsed by the TypoScript parser resulting in the shown error message. After removing (excluding should also work) the node_modules folder, everything worked as expected.

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