bug#23685: Emacs 25.0.94.1; Undo is clumping together delete-forward-char commands from distant parts of the buffer.

[Alan Mackenzie <acm@muc.de>]

This isn't a bug, so closing.
The problems below only occur in some (undetermined) circumstances,
possibly when edebug is active.

-- 
Alan Mackenzie (Nuremberg, Germany).

In article <mailman.733.1464905650.1216.bug-gnu-emacs@gnu.org> you wrote:
> Hello, Emacs.

> I'm using Emacs 25.0.94.1, built as follows:

> In GNU Emacs 25.0.94.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.7)
>  of 2016-05-24 built on acm
> Repository revision: 2671179b11a9423792aaf2439a26a2562679c086
> Configured using:
>  'configure --with-tiff=no --with-gif=no --with-gpm'

> Configured features:
> XPM JPEG PNG RSVG SOUND GPM DBUS GSETTINGS NOTIFY ACL GNUTLS LIBXML2
> FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

> I have the following in a buffer:
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> #define FOO(bar) char bar [] = R"bar(bar)bar"

> char baz [] = R"baz(baz)foo";
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

> I delete the "a" from Line 1 col 34 with `delete-forward-char' (bound to
> the <deletechar> key).  Then I move to Line 3, and likewise delete the
> "o" in column 25.

> Now I attempt to undo the last deletion with C-_.  Maddeningly, this
> undoes both of the two last disjoint deletions.  It appears to be
> impossible to undo only the last of these deletions.  This has caused me
> some inconvenience in testing.  There is no customizable option by which
> this irritating behaviour can be disabled.  It is surely a bug.

> I can understand coalescing a sequence of undos in the same place, much
> as consecutive `self-insert-command's are coalesced into a single group
> for undo.  However, coalescing two deletions separated by movement
> commands into a single undo group is going too far.

> Can we possibly have a rethink on this before Emacs 25 goes out?

> -- 
> Alan Mackenzie (Nuremberg, Germany).