Git Merge Conflict Resolution.md

Merge Conflict Resolution

If merging a topic branch into a version branch causes a conflict, eg: In these examples, 1.2 is the version branch, A and B have already been merged in, and we're trying to merge in C.

git checkout 1.2
git merge A
git merge B                     
git merge C                     # Conflict!
git reset --hard                # Cancels the merge of C into 1.2

It is assumed that 1.2, A, B, and C all have 1.1 (latest production release) merged in. It is unknown at this point wether C conflicts with A or B. There are multiple ways to resolve this.

Fixing the conflict between the Topic Branch and the Version Branch

Make the version branch a dependency

Pro's: Quick & Easy Con's: Pollutes your topic branch with all of the other stuff in the release

git checkout C
git merge 1.2                  # Conflict!
# fix the conflict

Fix the conflict on the Version Branch

Pro's: Quick & Easy Con's: Makes the Version Branch more complicated to rebuild

git checkout 1.2
git merge C                     # Conflict!
# fix the conflict
# add fix to tag card

Fixing the conflict between the Topic Branch and the conflicting Topic Branch

Determine the conflicting topic branch using a temporary merge testing branch.

git checkout C
git checkout -b C-merge-test
git merge A                     # It's fine
git merge B                     # Conflict!
git checkout C
git branch -D C-merge-test

We have determined that it is B that fails to merge with C

Make This Branch Include the other Branch

git checkout C
git merge B                     # Conflict!
# fix the conflict

Make the Other Branch Include This Branch

git checkout B
git merge C                     # Conflict!
# fix the conflict

Prevent the Conflict

Pro's: Clean Con's: Difficult & Timely

git checkout C
git merge B                     # Conflict!
# Look at the conflict source
git reset --hard                # Cancel the merge of B into C
# Modify the code
git merge B                     # Re-attempt the merge