When a git branch goes bad

Want to merge some good code into the master branch, but stymied by code you don’t care about causing a bunch of conflicts?
The other day, some crap got committed to master and pushed, accidentally. It didn’t belong. Since it was pushed to origin, we don’t want to change history*. When it was time to do a git-flow release, a bunch of conflicts stymied the merge from release branch into master. I wanted to say, “Merge this branch into master, but take all the code from the branch; don’t worry about what’s currently in master.”

There’s a merge strategy for merging in a branch and ignoring the changes into the branch: the “ours” merge strategy. But there’s no “theirs” merge strategy for choosing all the code from the branch. Here is one way to accomplish this:

1. Start the merge

if using git-flow to do a release: git flow release finish versionName
OR
general case of merging something into master (or whatever branch you like; master is an example):

git checkout master
git merge branchWithGoodCode

This leaves the merge open, with conflicts. git status shows the files successfully merged (these are in the index) and the files with conflicts (not yet in the index). While the merge is in progress, git is in a special state, something like the below diagram. The objective is to get all the right files into the index and then commit, which will complete the merge.

2. Get all the code from the branch 

git checkout MERGE_HEAD — .

Here, MERGE_HEAD means “the tip of the branch we’re trying to merge in.” MERGE_HEAD is a ref (pointer to a commit) that exists while a merge is in process. This command pulls the files from there into the working directory and index.
The “.” at the end is important: when a path is provided as the last argument to git checkout, then git updates the files without changing your current branch. git checkout with no path will switch to that branch. (The — is optional, but it makes that . harder to miss.)

3. Commit to finish the merge

git commit -m “Merge branchWithGoodCode, taking all files from branchWithGoodCode”
Hurray, now the tree looks like this: