FR: Specify multiple revisions in interdiff from/to

[CGamesPlay]

Is your feature request related to a problem? Please describe.
From #8265. I've got a PR from a non-JJ git user in revisions a..b. The author rebases their commit and modifies the changes, giving a new range c..d. If a..b was just b and c..d was just d, then I could use jj interdiff --from b --to d to see what changed, however because they are ranges, I can no longer use interdiff.

Describe the solution you'd like
It would be ideal if interdiff was able to accept entire revsets for both from/to arguments. That would transparently just squash both revsets into a single revision, and then proceed as normal.

Describe alternatives you've considered
The workaround is to do the first step manually:

1. Duplicate a..b & c..d
2. Squash a..b2 into b2 and c..d2 into d2
3. Run jj interdiff --from b2 --to d2
4. Run jj abandon b2 d2 and jj edit to go back to where you were when you started.

This is a very manual process that needlessly changes the working copy revision several times and can't easily be scripted.

Additional context
Add any other context or screenshots about the feature request here.

[yuja]

Perhaps, the requested feature is the same as (or very close to) #498?

[CGamesPlay]

It could be the same. The issue as written, copying git range-diff, it is definitely NOT what I am looking for. But the first comment is exactly what I am looking for, i.e. “generalized interdiff”.

[joyously]

Given the way you've written a..b, doesn't that mean that a is an ancestor of b?
I'm struggling to understand why you can't just interdiff or just diff the original b and d.

[CGamesPlay]

I agree, it really should just work. Except it's multiple revisions, and it doesn't.

$ jj interdiff -f main..d6a3eb26  -t main..bookmark-13a9
Error: Revset `main..d6a3eb26` resolved to more than one revision

[joyously]

I agree, it really should just work.

You are agreeing with yourself, not what I said. I'm asking about interdiff -f d6a3eb26 -t bookmark-13a9, which should encompass those ancestors. Or does that include too many ancestors?
I'm thinking that for a review, it needs to work with everything existing.

[CGamesPlay]

I'm asking about interdiff -f d6a3eb26 -t bookmark-13a9, which should encompass those ancestors. Or does that include too many ancestors?

Oh, my mistake. To answer directly: no, interdiff does not include the ancestors that I want to examine. I addressed that in my original message; perhaps a diagram would make this clearer:

a ──┬── q ── r ── s ── b
    │
    └── e ── f ── c ── w ── x ── y ── d

If I use interdiff --from b --to d, jj will internally rebase b onto y and compare with d, thereby dropping the changes in q, r, s, w, x, and y. What I actually want is to squash a..b into b2, then squash c..d into d2, and interdiff --from b2 --to d2 (as I mentioned in my original workaround).

[joyously]

OK, and plain diff -f b -t d ? (I don't really get what interdiff does. It's a diff of diffs?)

[CGamesPlay]

Plain diff -f b -t d would include changes in e and f, which is also not what I want (this is the point of interdiff: "excludes changes from other commits by temporarily rebasing --from onto --to's parents").