Re: disabling undo boundaries

[Phillip Lord]

Stefan Monnier <address@hidden> writes:

>> Actually, I have been thinking about this. What I worry about with this
>> is that we may be adding the same form of heuristic into undo.c as the
>> "insert an undo-boundary if the buffer has changed".
>
> Yes, because we do want this to happen, pretty much always (having
> changes accumulate without intervening boundary is actually a problem
> that can lead to nasty behaviors).
>
> There are exceptions, but they're rare.


Sorry for late reply -- been travelling.

The heuristic I was refering to is the "insert an undo-boundary if the
current-buffer has changed". Or, rather, insert an undo-boundary if some
*other* buffer has changed.

I think that the current undo-boundary behaviour wrt a single buffer
makes sense. It's the fact that inserting content into *that* buffer
forces an undo-boundary into *this* buffer. I don't know why Emacs does
this. In most cases, this is irrelevant and doesn't happen anyway, and
where you have a p-c-h or a-c-f it changes undo behaviour. I worry that
I am missing a good reason for this behaviour, but I have thought about
it and failed to come up with a reason; negative conclusions are always
worrisome, but what else can you do?

I'll write a patch to trunk and send it in, once my life has caught up,
then I can happily pass the buck of making the final decision to you:-)

Phil