Allow "at sign" `@` in BibTeX entry

[4e554c4c]

BibTeX doesn't support % as a comment character. Instead, the ordinary suggestion is to comment out fields by using @. Unfortunately the biblatex parser (and, by extension, hayagriva and typst) fails to parse BibTeX fields that begin with an @.

This crate seems to support the % character for commenting, but if it does not support @ for commenting then interoperability with BibTeX and Biber is limited.

Proposal

@article{foo,
   title={bar},
  year={2025},
  @location={Mom's Basement}
}

should parse as two entries, with the third "commented" entry removed.

[PgBiel]

Your link suggests that unknown fields are ignored, not that you should use @. Writing zzz-location={...} would work here for example. Is that not enough? Or are there cases where this @ is actually needed?

[4e554c4c]

The problem is not whether this is enough to "comment" out a field. Rather, it is an issue concerning compatibility between this library and actual BibTeX parsers. There are many bibliographies in the wild (mine included) which have these @ signs in field names, and if this crate is not able to parse them then that creates a lack of compatibility.

[PgBiel]

Okay. Just to better understand it, do you have more details about this syntax? Is it only valid at the start of a line, or of a field name, or can it also be used at the end of a line after a field? And do you have some more examples if there are other cases?

[4e554c4c]

I've done some deep digging into biber, and its Text::BibTex library. The lexer appears to actually have two distinct comment mechanisms The first is % comments, and the second is toplevel declarations of the form @comment(....) where anything within the .... has balanced parentheses and braces.

Other than that, I think biber doesn't really like @ in field names. I think this is something that only works with bibtex, and I belive that bibtex skips to the next line if it sees an @ sign anywhere other than toplevel.