Pull request workflow

The so-called "PR workflow" used by Godot is common to many projects using Git, and should be familiar to veteran free software contributors. The idea is that only a small number (if any) commit directly to the master branch. Instead, contributors fork the project (i.e. create a copy of it, which they can modify as they wish), and then use the GitHub interface to request a pull from one of their fork's branches to one branch of the original (often named upstream) repository.

The resulting pull request (PR) can then be reviewed by other contributors, which might approve it, reject it, or most often request that modifications be done. Once approved, the PR can then be merged by one of the core developers, and its commit(s) will become part of the target branch (usually the master branch).

We will go together through an example to show the typical workflow and associated Git commands. But first, let's have a quick look at the organization of Godot's Git repository.

Git source repository

The repository on GitHub is a Git code repository together with an embedded issue tracker and PR system.

Note

If you are contributing to the documentation, its repository can be found here.

The Git version control system is the tool used to keep track of successive edits to the source code - to contribute efficiently to Godot, learning the basics of the Git command line is highly recommended. There exist some graphical interfaces for Git, but they usually encourage users to take bad habits regarding the Git and PR workflow, and we therefore recommend not to use them. In particular, we advise not to use GitHub's online editor for code contributions (although it's tolerated for small fixes or documentation changes) as it enforces one commit per file and per modification, which quickly leads to PRs with an unreadable Git history (especially after peer review).

See also

The first sections of Git's "Book" are a good introduction to the tool's philosophy and the various commands you need to master in your daily workflow. You can read them online on the Git SCM website. You can also try out GitHub's interactive guide.

The branches on the Git repository are organized as follows:

  • The master branch is where the development of the next major version occurs. As a development branch, it can be unstable and is not meant for use in production. This is where PRs should be done in priority.

  • The stable branches are named after their version, e.g. 3.1 and 2.1. They are used to backport bugfixes and enhancements from the master branch to the currently maintained stable release (e.g. 3.1.2 or 2.1.6). As a rule of thumb, the last stable branch is maintained until the next minor version (e.g. the 3.0 branch was maintained until the release of Godot 3.1). If you want to make PRs against a maintained stable branch, please check first if your changes are also relevant for the master branch, and if so make the PR for the master branch in priority. Release managers can then cherry-pick the fix to a stable branch if relevant.

  • There might occasionally be feature branches, usually meant to be merged into the master branch at some time.

Forking and cloning

The first step is to fork the godotengine/godot repository on GitHub. To do so, you will need to have a GitHub account and to be logged in. In the top right corner of the repository's GitHub page, you should see the "Fork" button as shown below:

../../_images/github_fork_button.png

Click it, and after a while you should be redirected to your own fork of the Godot repo, with your GitHub username as namespace:

../../_images/github_fork_url.png

You can then clone your fork, i.e. create a local copy of the online repository (in Git speak, the origin remote). If you haven't already, download Git from its website if you're using Windows or macOS, or install it through your package manager if you're using Linux.

Note

If you are on Windows, open Git Bash to type commands. macOS and Linux users can use their respective terminals.

To clone your fork from GitHub, use the following command:

$ git clone https://github.com/USERNAME/godot

Note

In our examples, the "$" character denotes the command line prompt on typical UNIX shells. It is not part of the command and should not be typed.

After a little while, you should have a godot directory in your current working directory. Move into it using the cd command:

$ cd godot

We will start by setting up a reference to the original repository that we forked:

$ git remote add upstream https://github.com/godotengine/godot
$ git fetch upstream

This will create a reference named upstream pointing to the original godotengine/godot repository. This will be useful when you want to pull new commits from its master branch to update your fork. You have another remote reference named origin, which points to your fork (USERNAME/godot).

You only need to do the above steps once, as long as you keep that local godot folder (which you can move around if you want, the relevant metadata is hidden in its .git subfolder).

Note

Branch it, pull it, code it, stage it, commit, push it, rebase it... technologic.

This bad take on Daft Punk's Technologic shows the general conception Git beginners have of its workflow: lots of strange commands to learn by copy and paste, hoping they will work as expected. And that's actually not a bad way to learn, as long as you're curious and don't hesitate to question your search engine when lost, so we will give you the basic commands to know when working in Git.

In the following, we will assume as an example that you want to implement a feature in Godot's project manager, which is coded in the editor/project_manager.cpp file.

Branching

By default, the git clone should have put you on the master branch of your fork (origin). To start your own feature development, we will create a feature branch:

# Create the branch based on the current branch (master)
$ git branch better-project-manager

# Change the current branch to the new one
$ git checkout better-project-manager

This command is equivalent:

# Change the current branch to a new named one, based on the current branch
$ git checkout -b better-project-manager

If you want to go back to the master branch, you'd use:

$ git checkout master

You can see which branch you are currently on with the git branch command:

$ git branch
  2.1
* better-project-manager
  master

Be sure to always go back to the master branch before creating a new branch, as your current branch will be used as the base for the new one. Alternatively, you can specify a custom base branch after the new branch's name:

$ git checkout -b my-new-feature master

Updating your branch

This would not be needed the first time (just after you forked the upstream repository). However, the next time you want to work on something, you will notice that your fork's master is several commits behind the upstream master branch: pull requests from other contributors would have been merged in the meantime.

To ensure there won't be conflicts between the feature you develop and the current upstream master branch, you will have to update your branch by pulling the upstream branch.

$ git pull --rebase upstream master

The --rebase argument will ensure that any local changes that you committed will be re-applied on top of the pulled branch, which is usually what we want in our PR workflow. This way, when you open a pull request, your own commits will be the only difference with the upstream master branch.

While rebasing, conflicts may arise if your commits modified code that has been changed in the upstream branch in the meantime. If that happens, Git will stop at the conflicting commit and will ask you to resolve the conflicts. You can do so with any text editor, then stage the changes (more on that later), and proceed with git rebase --continue. Repeat the operation if later commits have conflicts too, until the rebase operation completes.

If you're unsure about what is going on during a rebase and you panic (no worry, we all do the first few times), you can abort the rebase with git rebase --abort. You will then be back to the original state of your branch before calling git pull --rebase.

Note

If you omit the --rebase argument, you will instead create a merge commit which tells Git what to make of the two distinct branches. If any conflicts arise, they would be resolved all at once via this merge commit.

While this is a valid workflow and the default behavior of git pull, merge commits within PRs are frowned upon in our PR workflow. We only use them when merging PRs into the upstream branch.

The philosophy is that a PR should represent the final stage of the changes made to the codebase, and we are not interested in mistakes and fixes that would have been done in intermediate stages before merging. Git gives us great tools to "rewrite the history" and make it as if we got things right the first time, and we're happy to use it to ensure that changes are easy to review and understand long after they have been merged.

If you have already created a merge commit without using rebase, or have made any other changes that have resulted in undesired history, the best option is to use an interactive rebase on the upstream branch. See the dedicated section for instructions.

Tip

If at any time you want to reset a local branch to a given commit or branch, you can do so with git reset --hard <commit ID> or git reset --hard <remote>/<branch> (e.g. git reset --hard upstream/master).

Be warned that this will remove any changes that you might have committed in this branch. If you ever lose commits by mistake, use the git reflog command to find the commit ID of the previous state that you would like to restore, and use it as argument of git reset --hard to go back to that state.

Making changes

You would then do your changes to our example's editor/project_manager.cpp file with your usual development environment (text editor, IDE, etc.).

By default, those changes are unstaged. The staging area is a layer between your working directory (where you make your modifications) and the local Git repository (the commits and all the metadata in the .git folder). To bring changes from the working directory to the Git repository, you need to stage them with the git add command, and then to commit them with the git commit command.

There are various commands you should know to review your current work, before staging it, while it is staged, and after it has been committed.

  • git diff will show you the current unstaged changes, i.e. the differences between your working directory and the staging area.

  • git checkout -- <files> will undo the unstaged changes to the given files.

  • git add <files> will stage the changes on the listed files.

  • git diff --staged will show the current staged changes, i.e. the differences between the staging area and the last commit.

  • git reset HEAD <files> will unstage changes to the listed files.

  • git status will show you what are the currently staged and unstaged modifications.

  • git commit will commit the staged files. It will open a text editor (you can define the one you want to use with the GIT_EDITOR environment variable or the core.editor setting in your Git configuration) to let you write a commit log. You can use git commit -m "Cool commit log" to write the log directly.

  • git commit --amend lets you amend the last commit with your currently staged changes (added with git add). This is the best option if you want to fix a mistake in the last commit (bug, typo, style issue, etc.).

  • git log will show you the last commits of your current branch. If you did local commits, they should be shown at the top.

  • git show will show you the changes of the last commit. You can also specify a commit hash to see the changes for that commit.

That's a lot to memorize! Don't worry, just check this cheat sheet when you need to make changes, and learn by doing.

Here's how the shell history could look like on our example:

# It's nice to know where you're starting from
$ git log

# Do changes to the project manager with the nano text editor
$ nano editor/project_manager.cpp

# Find an unrelated bug in Control and fix it
$ nano scene/gui/control.cpp

# Review changes
$ git status
$ git diff

# We'll do two commits for our unrelated changes,
# starting by the Control changes necessary for the PM enhancements
$ git add scene/gui/control.cpp
$ git commit -m "Fix handling of margins in Control"

# Check we did good
$ git log
$ git show
$ git status

# Make our second commit
$ git add editor/project_manager.cpp
$ git commit -m "Add a pretty banner to the project manager"
$ git log

With this, we should have two new commits in our better-project-manager branch which were not in the master branch. They are still only local though, the remote fork does not know about them, nor does the upstream repo.

Pushing changes to a remote

That's where git push will come into play. In Git, a commit is always done in the local repository (unlike Subversion where a commit will modify the remote repository directly). You need to push the new commits to a remote branch to share them with the world. The syntax for this is:

$ git push <remote> <local branch>[:<remote branch>]

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