Recent diff-mode changes feel slow with TRAMP

[Dima Kogan]

Hi.

There were some diff-mode updates recently that (I think) are making
emacs really slow under some conditions. Scenario:

- I'm working on a remote project via TRAMP and SSH
- There're a number of local changes
- I hit C-x v D    (vc-root-diff)

This runs something like "git diff" remotely. That command constructs a
patch. Previously emacs would simply load this patch into a buffer,
fontify it, and call it done. I THINK what's happening now is that in
addition, each file mentioned in the patch is loaded by emacs. I don't
know what emacs is doing with those files, but file loading is
potentially very slow with TRAMP, and we shouldn't be doing this by
default.

I haven't dug deeply here at all. I just see that after hitting C-x v D
I now have to sit here for a few minutes while emacs figures out what
it's doing. Is it loading all the files? Why?

I'm not subscribed to the list right now, so please Cc me in replies.

Thanks!
dima