bug#23906: 25.0.95; Undo boundary after process output is not consistent

[Markus Triska]

phillip.lord@russet.org.uk (Phillip Lord) writes:

> It is sufficient though, to restore the old behaviour and fix the
> regression you have, which is the point of this bug!

> We can think about doing something better (and which would work for
> viper also -- as Stefan says, the current solution has some issues). But
> I am not sure what this would look like at the moment.

Please let us use this opportunity to fix the more general case
too. Stefan agreed that the following primitives would work:

    -) undo-begin-transaction
       Starts a new transaction.
    -) undo-end-transaction
       Ends the most recently started undo transaction.

The effects of all commands between would be undone as a single unit.

Introducing new variables that only change how the process timer works
would be made completely obsolete by such a solution: It would simply
fall out as one special case of such transactions, benefit ediprolog and
(very likely) Viper, and also other programs. Personally, I would have
no use case for only changing the process timer if such transactions
were available, since this is only one special case for me, even though
it is the one that is described in the very first post of this report.

I hope this approach or an equivalent one is possible in Emacs, and I
would be very grateful if you could look into this.

Thank you and all the best!
Markus