DNF feature request: usefully undo updates-testing transactions, or clarify instructions

[Andrew Lutomirski]

I just messed up and did:

# dnf --enablerepo=updates-testing upgrade

and upgraded everything instead of just the thing I was trying to
upgrade.  I want to undo that, but it seems to be impossible.

# dnf history undo 119
[...]
No package libreoffice-base-1:4.3.5.2-11.fc21.x86_64 available.
Error: An operation cannot be undone

# dnf distro-sync
Using metadata from Tue Feb 24 17:15:49 2015
Error: package ghostscript-x11-9.15-6.fc21.x86_64 requires
ghostscript(x86-64) = 9.15-6.fc21, but none of the providers can be
installed

Gee, thanks.

As it happens, # dnf distro-sync --allowerasing works.  Perhaps # dnf
distro-sync could suggest --allow-erasing.

Also, there's a bug here:

# dnf distro-sync --allowerasing
[...]
Transaction Summary
================================================================================
Downgrade  132 Packages

Total download size: 186 M
Is this ok [y/N]: y

So I shouldn't have needed --allowerasing in the first place.

An alternative would be to add a most that undoes the last transaction
and updates at the same time.  That way it could undo my accidental
transaction but only depend on versions of packages that still exist
in updates.

--Andy