bug#73484: 31.0.50; Abolishing etags-regen-file-extensions

[Dmitry Gutov <dmitry@gutov.dev>]

On 29/09/2024 11:25, Eli Zaretskii wrote:
> I understand that we need to disable the Fortran and C fallbacks to
> avoid false positives, but what do we want to do if the fallbacks are
> disabled and no suitable language parser is found using the file name?
> Just skip the file and do nothing? emit a warning? something else?

Just do nothing. We'd really want to delegate language detection to 
etags rather than doing it inside Elisp - the latter is slower and 
ultimately more limited. But for that etags needs to have a reliable 
detection logic, one without too many false positives (and IME false 
positives here are worse than false negatives, because scanning too much 
can often mean both wrong tags and long scans, and a completion table 
that gets too large because of bogus tags).

For shebangs in particular, however, see Francesco's very good 
explanation. And detecting shebangs in Lisp would not be practical -- 
too slow.