bug#69266: 30.0.50; bibtex-parse-entry misreads escaped \}

[Roland Winkler <winkler@gnu.org>]

On Sun, Feb 25 2024, Arash Esbati wrote:
> The following code doesn't throw an error for me with LaTeX2e
> <2023-11-01> patch level 1:
>
> \documentclass{article}
>
> \begin{document}
>
> \noindent \{x\}\\
> \textbraceleft x\textbraceright
>
> \end{document}

Indeed, "\{" must have become available as a command outside math mode
after I learned LaTeX many years ago.  (I believe it is still correct to
say that from LaTeX's perspective "\{" is a macro that is very different
from escaping available in other programming languages.)

> Would you reconsider this if Biber handles \} correctly?  I didn't
> test it, though.

I am happy to take advice from more advanced biber / biblatex users.
For the fun of it, I just created my first LaTeX document using biber /
biblatex.  That worked fine with balanced braces.  But it choked with a
biber error message when a biblatex field contained a single "\{".

Biber uses btparse to parse BibTeX files. The BibTeX data language, as
recognized by btparse is explained here

https://metacpan.org/dist/Text-BibTeX/view/btparse/doc/bt_language.pod

My reading of this document is that btparse does no take steps to deal
with "escaped braces" inside a field.