Git Fixing a Merge Broken by Base Branch Rebase

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Overview

TODO: NOT RE-TESTED YET. DO THIS FIRST TIME YOU NEED THIS.

You may have found yourself in the situation when you attempt to merge just to find out that the base branch is rebased. A typical symptom for this situation is that Git warns about unexpected merge conflicts. What used to be a clean merge suddenly turns into a merge with a large number of conflicts, usually caused by files you don't recognize and don't have anything to do with. This article contains a procedure that will help you recover from that situation and render your merge viable again. It assumes that the base branch is "develop", and the head branch to be merged is "topic/something".

Procedure

First, checkout the problematic topic branch and identify the base ("develop") branch commit the head branch originates from:

git checkout topic/something
git log

The "develop" branch commit will be the first commit that is not "yours" - that is, the first commit that is not a commit created by you on the "topic/something" branch.

Sync repository state:

git fetch --prune

Rebase the head branch commits at the proper location on the base branch. Note that in the example below, "0742faad3a6c8633f0625e29cf215a6f0f2e189a" is the commit identified previously:

git rebase --onto origin/develop --fork-point 0742faad3a6c8633f0625e29cf215a6f0f2e189a

Fix the upstream head branch, doing a "dry run" first:

git push -n --force
git push --force

Synchronize the state of local "develop" branch with the state of its tracking branch:

git checkout develop
git reset --hard origin/develop