Diff stash against dirty current state

[p3lim]

It would be handy if there would be a way to show a diff between the contents of a stash against the current state (committed + unstaged + untracked) of a repository.

I have a tendency to stash changes because I need to pull in patches upstream, and if those changes affect the changes I stashed I'd like to see them before I attempt to apply the stash. At present it just diffs them against the state at which the stash was created.

[kaste]

This sounds like a very useful addition but we need an implementation idea first.