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

[Roland Winkler <winkler@gnu.org>]

Ihor Radchenko <yantar92@posteo.net> writes:
> According to https://www.bibtex.org/SpecialSymbols/, characters that
> conflict with Bibtex format description can be \-escaped.

I believe the above webpage is incorrect.  If I put something like \}
into a BibTeX field, BibTeX complains about unbalanced braces.
This is with BibTeX, Version 0.99d (TeX Live 2022/Debian).
The parsing algoritm used by BibTeX is very simple.  Generally,
BibTeX fields should contain valid LaTeX code.  So something
like
     title = "$\}$tex",

should work with BibTeX, but it gives the same error message
"unbalanced braces".

Emacs bibtex mode follows the capabilities of BibTeX itself.  I believe
it would not make sense to try to be smarter than that if, in the end,
this is not compatible anymore with BibTeX itself.

I guess one could submit here a bug report / feature request for BibTeX.
But BibTeX has been around for many decades with this limited feature set.

Nowadays, there is also biblatex.  It's intended as a successor for
BibTeX.  But it is something I know little to nothing about because in
my world (physics), everyone I know still uses BibTeX.  Essentially,
biblatex entries still use the same format as BibTeX entries.  I do not
know whether biblatex would deal with something like the above in a
smarter way.  

These BibTeX fields should contain valid LaTeX code.  But from (La)TeX's
perspective, in the string "$\}$" the backslash is not an escape
character for what follows, but \} is a macro that's defined inside TeX
math mode.  Also, the meaning of the statement "valid LaTeX code" can be
heavily redefined within (La)TeX.  Take a look at texinfo files that TeX
can digest.  So a smart BibTeX parser would require (La)TeX itself working
in the background.

In practical terms (for many years) I have never experienced this to be
a constraint when working with BibTeX.  So changing / improving this may
have a low priority among BibTeX / biblatex maintainers.