How to compare a change through rebasing?

[CGamesPlay]

Hello! I'm doing code review of a large change in an active repository. The PR has been modified: previous commits perhaps changed, new commits added, and the whole stack rebased. I want to compare the changes between two PR versions, excluding all other changes. How can I do this?

It felt like jj interdiff would be the appropriate command, but that only accepts a single revision, so I can't use it to compare the entire stack. jj diff will obviously include the changes between the respective parents, so that's not useful.

$ jj log -T builtin_log_redacted -r main..bookmark-13a9 -r main..d6a3eb26
○  lpvopmwo user-fd9d 2025-12-05T14:11:00+01:00 bookmark-13a9 5529807e
○  orosvlry user-fd9d 2025-12-05T09:13:27+01:00 d09445ec
○  ruqzvsqn user-fd9d 2025-12-05T07:58:33+01:00 e9133ae6
○  nuuusuzt user-fd9d 2025-12-05T07:58:31+01:00 a6a9a68e
○  tlrzyzyv user-fd9d 2025-12-05T07:56:16+01:00 65d40d83
○  vszlrkzo user-fd9d 2025-12-05T07:56:16+01:00 200f54ed
○  owtkwkmz user-fd9d 2025-12-05T07:56:16+01:00 65522aba
○  xsmyswyy user-fd9d 2025-12-05T07:56:16+01:00 8e725561
○  kquvnwsq user-fd9d 2025-12-05T07:56:12+01:00 e754e0e2
~

○  zxwtnluq hidden user-fd9d 2025-12-03T10:29:08+01:00 d6a3eb26
○  slspwyyu hidden user-fd9d 2025-12-03T10:29:08+01:00 e712f39b
○  stmuyoor hidden user-fd9d 2025-12-03T10:29:08+01:00 2abc6dcf
○  kqmsllzm hidden user-fd9d 2025-12-03T10:29:08+01:00 19ba8b73
○  qvqzuwxr hidden user-fd9d 2025-12-03T10:29:08+01:00 77c88ae2
○  ywtvkqms hidden user-fd9d 2025-12-03T10:29:08+01:00 556ef28d
○  oxuwyvzm hidden user-fd9d 2025-12-03T10:29:07+01:00 3c40cb98
~

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

[CGamesPlay]

I found a path to getting this, by squashing all the commits into one change and then using interdiff. This works, but it's more manual to set up and clean up afterwards. I hope jj can provide something that does this without needing to manually create/clean the target changes.

jj new d6a3eb26
jj squash -f main..@- -t @
jj new bookmark-13a9
jj squash -f main..@- -t @
jj interdiff -f $OLD_CHANGE_ID -t $NEW_CHANGE_ID

[martinvonz]

I think your guess that jj interdiff -f main..d6a3eb26 -t main..bookmark-13a9 would work makes sense.

There's also FR #498 for adding something like git range-diff. With that proposal, jj interdiff would work a bit differently because it would have to say which changes (i.e. the things identified by change IDs) have been added and removed between the two ranges.

In your example, it looks like the other person does not use jj, so their commits don't have preserved change IDs. That means that a naive jj range-diff would present it as all old commits being removed and all new ones being added. What Git does is to make a guess based on the diffs and/or commit messages or author/timestamps (I don't remember which). We could do the same, but I find that quite ugly. I would rather base it on just the change ID. But that would mean that when interacting with commits coming from Git, we would not be able to show anything useful. Your proposed jj interdiff -f <range> -t <range> would still work, though, and it sounds like it would provide what you cared about in this case (i.e. just the diff).

[CGamesPlay]

Thanks for the insight. Sounds like jj doesn't support this use case at this time. I've created #8281 to track.