[Bug]: branch revert returns 'no changes' error despite actual differences between commits

[daniel-leicht]

What happened?

Description

When attempting to revert a branch to a previous commit/tag using lakectl branch revert, the command fails with
a "no changes" error (400 Bad Request), even though there are confirmed differences between the current branch
state and the target commit.

Steps to Reproduce

1. Have a repository with a branch (e.g., main) that has progressed beyond a tagged commit
2. Attempt to revert the branch to the tag:

   lakectl branch revert lakefs://deltalake-tables/main before-rerun -y
   

Expected Behavior

The revert operation should succeed and create a new commit that undoes the changes, reverting the branch state to
match the specified tag/commit.

Actual Behavior

The command fails with:

Branch: lakefs://deltalake-tables/main
update branch: no changes
400 Bad Request

This occurs despite there being many actual changes between the current branch state and the target tag.

Environment

• lakeFS Server Version: 1.73.0 (Official Docker container)
• lakectl Version: 1.70.1 (Windows)
  Using Minio as S3 backend.

Additional Context

The "no changes" detection appears to be incorrect in this scenario. The branch has progressed significantly from
the tagged commit, so the revert should detect and reverse those changes."
Create GitHub issue for lakeFS bug

Also, when attempting to see the diff, it comes back empty:

lakectl diff "lakefs://deltalake-tables/main" "lakefs://deltalake-tables/before-rerun"
Left ref: lakefs://deltalake-tables/main
Right ref: lakefs://deltalake-tables/before-rerun

• There are over 10 commits between the last commit to the commit tagged "before-rerun". I even added a new file via the Web UI and committed, still I get the same result.
• The issue also happens when entering the commit id instead of the tag name.
• --allow-empty-commit in the revert command doesn't help and the revert command doesn't fail but still doesn't do the actual expected revert.

Just a guess: it seems that the LakeFS server cannot see the diff between these commits and this is the root cause for the issue.

lakeFS version

1.73.0

How lakeFS is installed

Docker container

Affected clients

lakectl 1.70.0 and (lakefs==0.14.0, lakefs-sdk==1.72.0 for Python)

[arielshaqed]

Hi @daniel-leicht and @ssam18!

Thanks for your efforts here. Unfortunately this is expected documented behaviour, and I will have to close this issue as "not a bug". I would like to explain why.

Like Git, lakeFS supports two kinds of diffs. Unfortunately it gives them different names.

• A two-way diff shows the symmetric differences between the two refs. This is not the default.
• A three-way diff shows which those changes in the source that a merge would apply to the destination. As such, any changes from the base to the destination will not show - except that they may cause a conflict.

So you might see the changes you expect to see if you add --two-way to your diff command.

In the case of reverts, you would revert the merges into your branch. This works probably best if you do it in reverse order.

You are very much invited to the #help and #dev channels on the lakeFS Slack server.