Equivalent of "bzr diff -rancestor:"

[Stefan Monnier]

I can't seem to figure out how to do the above.

Say, I'm on local branch "foo" which tracks a remote branch "foo", and
I'd like to see what are the changes on this branch foo compared to "master".

In Bazaar, I'd do something like "bzr diff -r ancestor:<master>"
but I can't find any equivalent in "man gitrevisions".

The best I can come up with is to arrange for "foo" to be uptodate with
respect to "master", and then I can just do "git diff <master>", but
sometimes it's inconvenient/impractical to be "uptodate".


        Stefan