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Re: disabling undo boundaries

From: Stefan Monnier
Subject: Re: disabling undo boundaries
Date: Wed, 13 May 2015 08:32:59 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)

> My fault for not being clear.  AFAICT, undo-boundary does not set
> last_undo_buffer at all.

Oh, indeed, it sets last_boundary_buffer but not last_undo_buffer!

> I'm still trying to understand the reason behind the logic in the first
> place; unfortunately, the code seems to predate the earliest VC records.

IIUC the reason is for modifications in another buffer that take place
either within a command or between commands (e.g. process output), so
they don't accumulate arbitrarily within a single undo-boundary.

E.g. if you have a command "add timestamp to log buffer" which you
typically use from another buffer then, without this logic, running this
command 100 times would result in all entries in the buffer being lumped
together into a single undo-unit, so you couldn't undo them separately.


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