bug#50202: bibtex-mode: unescaped dollar sign in file field leads to wrong highlighting

[Roland Winkler <winkler@gnu.org>]

On Mon, Aug 22 2022, Lars Ingebrigtsen wrote:
> Yuu Yin <yuuyin@protonmail.com> writes:
>
>> - bibtex-mode enabled,
>> - and a BibTeX entry which has as value for file field a path that
>> has dollar sign ~
>> /path/to/file $ name.ext~
>>
>> bibtex-mode doesn't recognizes that the dollar sign is verbatim for
>> the file field, leading to wrong highlighting.
>
> This behaviour is still present in Emacs 29.  Perhaps Roland has some
> comments; added to the CCs.

A field "file" is, I believe, not part of standard BibTeX.  So the above
is somewhat pushing the limits of BibTeX mode.

From a more practical perspective, I need to say that the above problem
reaches the limits of my knowledge of how font-lock works in general and
how it deals with the (La)TeX delimiter "$" in particular.  Occassionally,
unpaired "$" give me strange results in LaTeX documents, though I have
no recipe to illustrate this.

I believe the above problem would require that BibTeX mode first parses
the BibTeX entries.  Then it uses different syntax tables for normal
fields and the file field.  I do not know how feasable this is, in
particular with larger BibTeX files.

I added Stefan to the CCs.  Long time ago, he helped me with font-lock
for BibTeX mode.  Maybe he has some comments.

Personally, I use a completely different strategy for associating file
names with BibTeX entries: the BibTeX autokey machinery generates the
nondirectory part of the filename that I associate with an entry.  And
find-dired locates the file, whereever it resides under a certain
directory.  So there is no file field at all that would require
maintenance.

Roland