A separate commit for conflict resolution with git merge

Question

I'm trying to merge a big topic branch into the master, but I want a separate commit that shows how the conflict resolution happened. The goal is to have one commit that shows "these files conflicted and how they conflicted" and the next commit would show "this is how the conflicts were resolved". I.e. the first commit would contain the conflict markers.

The reason for this is that the big topic branch has been reviewed and tested, as has the master branch. Of the merge, we want to review only the parts that needed some work (conflicts and other merge work).

Here's what I'm doing this far:

git checkout master
git checkout -b merge-from-topic
git merge topic

To record the files that have conflicts, I use a temporary file:

git diff --name-only --diff-filter=U >conflicts.txt

First I simply add those files, with the conflict markers, to a commit:

xargs git add <conflicts.txt
git commit

Then I create another branch (for review purposes) in which I'd like to do the conflict resolution:

git checkout -b resolve-merge-from-topic

To restore the conflicts, I tried

xargs git reset HEAD^ -- <conflicts.txt

but then git mergetool said that none of the files need merging although files in my working tree had conflict markers.

How do I restore files listed in conflicts.txt, so that I can use git mergetool on them?

I'm also open to other ways of getting the "separate commit for conflict resolution" effect.

Answer 1

git merge will leave conflict markers.

You then (usually) invoke git mergetool (with the --tool of your preference) to resolve the conflicts. Most of the time, this will result in staged changes. This you want to change (e.g. using git reset).

Now commit the 'raw' merge in isolation, and subsequently git add . && git commit -m 'resolutions' or git commit -am 'resolutions' to add the conflict resolutions.

Note this leaves you with a 'broken' build at the merge boundary revision.

In steps:

git checkout -b be_merged       # start a temp branch for the merge (safety)

git merge --no-commit diverge   # initiate merge from a diverged branch
git status                      # shows conflicts
git mergetool                   # resolve them as always
git status                      # shows resolutions as staged
git reset                       # unstage the changes
git status                      # shows unstaged changes (good!)
git commit -m 'merge, conflicts pending'   # commit the merge
git commit -am 'conflicts resolved'        # commit the resolutions

Answer 2

if you are really insistent on getting the merge history, then your best bet is to use git-imerge

AFAIK the git imerge gives you a choice if the merging history should be preserved or not

REF:

1. http://softwareswirl.blogspot.de/2013/05/git-imerge-practical-introduction.html

an exert from the author's blog:

git merge pain

• You need to resolve one big conflict that mixes up a lot of little changes on both sides of the merge. (Resolving big conflicts is hard!)
• Merging is all-or-nothing:
  1. There is no way to save a partly-done merge, so
     • You can't record your progress.
     • You can't switch to another branch temporarily.
     • If you make a mistake, you cannot revert only part of the merge.
     • If you cannot resolve the whole conflict, there is nothing to do but start over.
  2. There is no way to test a partly-done merge--the code won't even build until the conflict is completely resolved.
• It is difficult to collaborate on a merge with a colleague.

which may be exactly why you require a conflict-commit in the first place.

---

On another hand, a different perspective:

The merging changes should be kept as minimal as possible on an trivial project Why this is being said is that a merge touching all of the files in the repository will make you have a real pain in the future. As if you are to merge your branch with some major branch , lets say you work on the production branch, while the releases are done from the release branch, a branch maintainer will just try to rebase your branch with his branch.

Now if you had a commit which touched all the files in the place, this is going to be a read bad stuff as the merge will most likely to have conflict (major one, probably the conflict-commit you made) so the maintainer will have 2 options:

1. merge it himself/herself
2. reject the merge and let you do the dirty work

its more likely that maintainer will be opting the latter as it's the easier one for him.

So this you'll be spending more time in resolving the conflicts than doing some productive work.

NOTE:

The second perspective is only applicable when you have feature topics that have simple span. When merging the feature topics having larger span, it's better to use imerge and keep the history, that way you'll have smaller commits and rebase will not be painful.