# Upgrading Your Bullet Train Application

<div class="rounded-md border bg-amber-100 border-amber-200 py-4 px-5 mb-3 not-prose">
  <h3 class="text-sm text-amber-800 font-light mb-2">
    Note: These ugrade steps have recently changed.
  </h3>
  <p class="text-sm text-amber-800 font-light mb-2">
    These instructions assume that you're doing a stepwise upgrade on an app that's already on version <code>1.4.0</code> or later.
  </p>
  <p class="text-sm text-amber-800 font-light">
    <a href="/docs/upgrades/options">Learn about other upgrade options.</a>
  </p>
</div>

## The Stepwise Upgrade Method

This method will ensure that the version of the Bullet Train gems that your app uses will stay in sync with the appliation framework provided by the starter repo.
If you've ever upgraded a Rails app from version to version this process should feel fairly similar.

## Pulling Updates from the Starter Repository

There are times when you'll want to update Bullet Train gems and pull updates from the starter repository into your local application.
Thankfully, `git merge` provides us with the perfect tool for just that. You can simply merge the upstream Bullet Train repository into
your local repository. If you haven’t tinkered with the starter repository defaults at all, then this should happen with no meaningful
conflicts at all. Simply run your automated tests (including the comprehensive integration tests Bullet Train ships with) to make sure
everything is still working as it was before.

If you _have_ modified some starter repository defaults _and_ we also happened to update that same logic upstream, then pulling the most
recent version of the starter repository should cause a merge conflict in Git. This is actually great, because Git will then give you the
opportunity to compare our upstream changes with your local customizations and allow you to resolve them in a way that makes sense for
your application.

### 1. Decide which version you want to upgrade to

For the purposes of these instructions we'll assume that you're on version `1.4.0` and are going to upgrade to version `1.4.1`.

### 2. Make sure you're working with a clean local copy.

```
git status
```

If you've got uncommitted or untracked files, you can clean them up with the following.

```
# ⚠️ This will destroy any uncommitted or untracked changes and files you have locally.
git checkout .
git clean -d -f
```

### 3. Fetch the latest and greatest from the Bullet Train repository.

```
git fetch bullet-train
git fetch --tags bullet-train
```

### 4. Create a new "upgrade" branch off of your main branch.

It can be handy to include the version number that you're moving to in the branch name.

```
git checkout main
git checkout -b updating-bullet-train-1.4.1
```

### 5. Merge in the newest stuff from Bullet Train and resolve any merge conflicts.

Each version of the starter repo is tagged, so you can merge in the tag from the upstread repo.

```
git merge v1.4.1
```

It's quite possible you'll get some merge conflicts at this point. No big deal! Just go through and
resolve them like you would if you were integrating code from another developer on your team. We tend
to comment our code heavily, but if you have any questions about the code you're trying to understand,
let us know on [Discord!](https://discord.gg/bullettrain)

One of the files that's likely to have conflicts, and which can be the most frustrating to resolve is
`Gemfile.lock`. You can try to sort it out by hand, or you can checkout a clean copy and then let bundler
generate a new one that matches what you need:

```
git checkout HEAD -- Gemfile.lock
bundle update
```

If you choose to sort out `Gemfile.lock` by hand it's a good idea to run `bundle install` just to make
sure that your `Gemfile.lock` agrees with the new state of `Gemfile`.

Once you've resolved all the conflicts go ahead and commit the changes.

```
git diff
git add -A
git commit -m "Upgrading Bullet Train to v1.4.1."
```

### 6. Run Tests.

```
rails test
rails test:system
```

### 7. Merge into `main` and delete the branch.

```
git checkout main
git merge updating-bullet-train-1.4.1
git push origin main
git branch -d updating-bullet-train-1.4.1
```

Alternatively, if you're using GitHub, you can push the `updating-bullet-train-1.4.1` branch up and create a
PR from it and let your CI integration do it's thing and then merge in the PR and delete the branch there.
(That's what we typically do.)