How to identify conflicting commits by hash during git rebase?

When I encounter a merge conflict using git rebase, how can I identify the source of the conflict in terms of commits, rather than just file differences?

I already know how to make (basic) use of git mergetool or git add before git rebase --continue, but sometimes the differences between files just isn't enough: I want to see the commit log and diff of the commit that just failed to be applied to the working tree.

I've read in other questions that git log --merge would show the parent commits if I were using git merge. I tried it anyways when I encountered a conflict and got told fatal: --merge without MERGE_HEAD?.

How can I identify the problematic commit?

Solution 1:

Short Answer

If it says

Patch failed at 0001 commit message for F

Then run

$ head -1 .git/rebase-apply/0001
From ad1c7739c1152502229e3f2ab759ec5323988326 Mon Sep 17 00:00:00 2001

To get the SHA ad1c77 of the failing commit, and then use git show ad1c77 to have a look at it.

Long Answer

Let's start with this tree:

A---B---C---D
     \
      E---F---G

$ git checkout G
$ git rebase D

When a rebase conflict occurs, it is a conflict between

• the upstream changes (C--D) from the the common ancestor (B) PLUS the already rebased changes and already resolved conflict (E') versus
• the patch of the next commit (F)

Let's see what happens:

1) A---B---C---D---E'          <- E patched and committed successfully as E'
2) A---B---C---D---E'---       <- failed to patch F onto E'

Here's the error message:

First, rewinding head to replay your work on top of it...
Applying: commit message for F
Using index info to reconstruct a base tree...
Falling back to patching base and 3-way merge...
Auto-merging 1.txt
CONFLICT (content): Merge conflict in 1.txt
Failed to merge in the changes.
Patch failed at 0001 commit message for F

First, you can see that it was F, because the commit message appears. However, if your commit messages all look like "foo", "documentation" or "some fixes", then this won't help, and you really want the SHA id ad1c77 or the contents of the patch.

Here's how to find out the real identity of F:

When it lists the rebase conflict, it will say something like:

Patch failed at 0001 commit message for F

Now look in .git/rebase-apply/, where you will find the patch file 0001:

$ ls .git/rebase-apply
0001          head-name     msg           orig-head     sign
0002          info          msg-clean     patch         threeway
apply-opt     keep          next          quiet         utf8
final-commit  last          onto          rebasing

The patch file includes the original commit-id

$ head -1 .git/rebase-apply/0001
From ad1c7739c1152502229e3f2ab759ec5323988326 Mon Sep 17 00:00:00 2001

You can then look at that.

There must be an easier way, but this works.

Note that the fact that the patch failed may be due to a different commit (if you are rebasing onto a common ancestor of HEAD and the rebase target). Finding that commit is rather more complicated, although you could try doing the rebase in reverse to find it:

$ git checkout D
$ git rebase G

Solution 2:

During a git rebase which stops to resolve conflicts, the following command will show the conflicting commit (all of it, not just the conflicting files), that is, your commit currently being replayed/rebased onto the new base, regardless of where you are up-to:

git show $(< .git/rebase-apply/original-commit)

If you want to see only the conflicts for a specific conflicting file (the one you are resolving), in-isolation:

git show $(< .git/rebase-apply/original-commit) -- /path/to/conflicting/file

No cats were abused in the construction of this answer :).

Solution 3:

Show the current/failed commit

This may be a new feature, but REBASE_HEAD gives you the commit where you're currently stopped (e.g. if the commit failed to apply). If you want to see the commit in full you can use

git show REBASE_HEAD

As a more verbose alternative, you can use git rebase --show-commit-patch. The docs say they are equivalent.

Show what's changed since you started your work

If you want to see what's changed between where you're rebasing from and where you're rebasing to, you can get a diff between the two branches. For example, if you're rebasing from master onto origin/master you can use:

git diff master..origin/master

Or if you want to see the changes as individual commits:

git log -p master..origin/master

If you'd prefer to use the hash or maybe are coming back to a rebase after a while and can't remember which branches you're rebasing, you can use git status to see the two branches. For example:

You are currently rebasing branch 'master' on 'b5284275'

Then, to see what's changed you can use:

git diff master..b5284275