You are correct that a protocol number has advantages in that it  guarantees
folks get a minimum version of GNU Emacs bashdb support. However given other
circumstances,  the real here benefit to everyone is negligible.

bashdb is not distributed as part of bash right now and in order to do any
sort of debugging you  need bashdb installed. So it's possible (in fact
likely) that folks will install GNU Emacs but not have this add-on and
things are broken. In theory the GNU Emacs gud code could check for the
presence of bashdb, but it doesn't yet (and it might be cumbersome to
write).

Furthermore, the issues we've been seeing aren't so much that the underlying
protocol changes (so things break), as much as where bugs  tend to get
reported, the speed of fixes, and frequency of user-visible releases of
minor improvements and enhancements. For example, the last change involved
changing a regular expression to accommodate Microsoft Windows. As part of
that fix, we added a little regression test for that case. I believe this
fix is part of the last release.

It is not clear that had the bug finder reported this to via the GNU Emacs
channels, the change would have be visible  to users as soon, or that there
would have been a regression test added. bashdb has and advantage or
disadvantage of being much smaller than GNU Emacs. Therefore we are able to
be more agile.

Finally, I think the argument is also equally valid the other way around
too. If gud had a protocol number,  it would help bashdb.el and other
add-ons, like the debugger for GNU Make for which there is a corresponding
GNU Emacs interface. That GNU Emacs lisp code  would check against  a
protocol number instead of GNU Emacs major/minor version numbers and adjust
accordingly.


On 2/25/07, Richard Stallman <rms@gnu.org> wrote:
>
>     To avoid users' confusion, we'd like to move bashdb related code(
> bashdb.el)
>      in gud.el to bashdb itself. So we can provide well updated bashdb.elin
>     bashdb release.
>
> Wouldn't it be better to have a protocol version number?
> Then Emacs could still have the code, but if you change the protocol,
> you would update the protocol version number.  Then the code in Emacs
> would say "you need to install bashdb.el from <wherever>.
>