Idea for C-x v u

[Richard Stallman]

It is definitely a good idea to check the diffs of a file before
reverting a change, but normally it's a waste of time for C-x v u to
do that because I will have done it manually.

However, if I ever forget to do that, it wouldn't hurt for C-x v u to
remind me.

So here's an idea.  Make C-x v d record the tick count of the buffer
when it was done.  Then C-x v u can show a diff, if you have not made
one of that buffer since the last edit in it.

This might be universally better than the two optional choices that
were previously proposed (either unconditionally show a diff, or never
show a diff).

Another idea is: if you have not made a diff since the last change in
the buffer, give an error, "Please look at a diff using C-x v = before
doing C-x v u".  It is more convenient for the user to make the diff
with a separate command than to examine it inside of yes-or-no-p.

Even if C-x v u does not make a diff, it should always call
yes-or-no-p.

-- 
Dr Richard Stallman
President, Free Software Foundation
51 Franklin St
Boston MA 02110
USA
www.fsf.org, www.gnu.org
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