Beginner's Guide to Contributing a Pull Request to Spacemacs

This guide is mostly a reproduction of @travisbhartwell's great introduction post on his blog. The primary changes pertain to Git branching strategy (and nomenclature) and the addition of git CLI commands. They're not meant to be used side-by-side and can be confusing if you do so. Please use either one or the other as a guide. (P.S. If reading such a long post is not your forte, he has also created a handy video tutorial covering the same topic.)

How to do it

Fork the Repository

Create the fork by visiting the Spacemacs project page on Github. If you happen to belong to organizations on Github, you will be prompted to select where to fork the repository; select your user in this case.

This will create a new repository for your user that is a mirror of the current state of the upstream repository.

Note/Copy the repository clone URL that is shown on the right-hand side of the page, part way down. This is needed when you clone your repository to your local filesystem in the next step.

Cloning your forked repository

Next, you need to clone your fork of Spacemacs to a local directory (preferably ~/.emacs.d). This can be done by typing git clone git@github.com:<YOUR USERNAME>/spacemacs.git ~/.emacs.d from the command line. Please ensure to backup your existing dot-emacs directory by typing mv ~/.emacs.d ~/.emacs.d.bk; just in case you decide to change your mind later.

Adding upstream Spacemacs

You now need to add Spacemacs upstream as an upstream to your clone.

Go to magit-status for the Spacemacs repository by doing SPC u SPC g s (Hit the spacebar, then u, then the spacebar again, then g, then s). Then enter the path of the Spacemacs repository, ~/.emacs.d, and hit RETURN.

If you're using the command line, open your Spacemacs directory by entering cd ~/.emacs.d and then hitting RETURN. Once you are in the Spacemacs directory, enter git status and then hit RETURN to know the current status (branch you are on, how many commits ahead or behind of origin you are etc.) of the repository.
Type M a to open the magit interface to add a new remote. Type the Remote name as upstream and Remote url as git@github.com:syl20bnr/spacemacs.git (or https://github.com/syl20bnr/spacemacs.git if you're using HTTPS). Type n when magit asks to set your remote.pushDefault to upstream.

From the command line, type git remote add -f upstream git@github.com:syl20bnr/spacemacs.git to achieve the same effect as above.

Updating your local repository

As it can happen from time-to-time, your fork of Spacemacs (which we will refer to as origin) can go out-of-sync with upstream. You need to ensure that you consistently keep updating from upstream.

Open magit-status for ~/emacs.d using the same sequence of steps detailed in the above section.
Switch to the develop branch, if you are not already there. Hit b b and type develop. If you haven't previously checked out the develop branch, instead of b b (or, branch checkout), you will need to type b c (or, create and checkout). It will prompt you for the branch to base it off of, select or type origin/develop, hit RETURN and then name the branch develop. Note that any time in the magit-status buffer, if you want to know what commands are available, just hit ?.

From the command line, you can type git checkout develop to check out the develop branch. If you haven't checked it out before, type git checkout -b develop origin/develop to check out a local develop branch based off of the origin/develop branch.
After you have the develop branch checked out, update it against the remote upstream repository. Hit F for Pulling. Then type r to rebase. Even though we don't yet have any local commits, it makes sense to rebase any unpushed commits on the remote branch so that they are up to date and can be merged without merge commits. Hit e to pull and rebase from elsewhere. Type upstream/develop in the subsequent popup to pull rebase from upstream.

From the command line, type git pull --rebase upstream develop to achieve the same effect as above.

After this is done, we want to restart Emacs to run any of the latest changes. Hit SPC q r to restart Emacs.
You will also need to push the newly rebased changes to your fork (origin repository) on Github. To do this, type P in the magit-status buffer. Then type u to push to origin/develop.

From the command line, type git push origin develop to achieve the same effect.

Creating a branch for your changes

Before any changes are made, you need to make a branch to put them in. You could just commit to the develop branch, push your changes to your fork, and then do a pull request off of that. However, this is not recommended since it is common to have multiple pull requests open at one time. Therefore it is simpler to do a branch per pull request. This also allows your branches to have meaningful names, and makes updating pull requests with maintainer feedback a much simpler process.

From the magit-status buffer, hit b c (or, create and checkout branch).
Magit will then prompt you for the branch you are branching off of. Choose develop.
Next, it will prompt you for a branch name. Seeing as git doesn't restrict branch names to a particular length, you can go for long descriptive names (like fix/spacemacs-home-buffer-bookmarks-jump) if you so desire.

From the command line, type git checkout -b fix/spacemacs-home-buffer-bookmarks-jump develop to achieve the same result as above.

Check out the Git book chapter on branching for an in-depth discussion of branching.

Making, committing, and pushing changes

Now that we have a branch we can make your changes. Go ahead and make the changes you want. After you have tested and are satisfied with them, you are ready to commit and push.

Go to the magit-status buffer again: SPC u SPC g s ~/.emacs.d RET.

On the command line, you can type git status to see a list of all the changes you have made to existing files or to see any new files that have been added.
Stage any unstaged changes you have made. Quickly: hit s on each line under Unstaged changes corresponding to a file you've changed. If you have added any new files, they will appear under Untracked files. Be sure to stage them as well by pressing s.

From the command line, type git add <FULL PATH TO FILE> to stage the changes. You can then type git diff --cached to see a diff of all the staged changes to verify whether everything is in order.
Hit c c to commit all staged changes.
Type a meaningful commit message. (See this post for a great explanation of what a good commit message is.) Helpfully, the diff of what you have changed is shown on the right-hand side for you to see what you did. Make the first line be a short subject describing the commit. Add a blank line and then in lines wrapped at 78, write a brief description of the changes and why. If you are fixing an issue that has been filed, include something along the lines of 'Fixes #2431'. Hit C-c C-c (that's Control and c together, and then again).

On the command line, type git commit and press RETURN. This will open a Vim interface where you can enter your commit message as detailed above. Then you can press :wq to commit your changes.
Hit P (or, Pushing). Type u to set the remote branch and push. Start typing origin/fix/spacemacs and it will finish the branch name for you -- origin/fix/spacemacs-home-buffer-bookmarks-jump. Hit RETURN.

From the command line, type git push origin fix/spacemacs-home-buffer-bookmarks to push your changes to your fork.

Making the pull request

You are now ready to submit your pull request. Switch back to your browser to the page for your fork.

Github will show your recently pushed branches near the top, in a yellow box. Refresh your page if you don't see this. Click the green "Compare & pull request" button.
In the next screen, Github will prompt you for a branch to compare against. By default it will show base: master. You want to select develop here. It may take a minute for the page to update after you have selected the develop branch.
If you've done everything right, it will be able to cleanly merge your commit and will indicate so. It will then pull from your commit message the subject and description. If you've written a good commit message, there should be no need to add anything here. Click Create pull request.

Congratulations! There you go, you have created your first pull request. Hopefully the project developers will like your pull request and merge it.

Updating the pull request

As is often the case, the maintainers might offer feedback on your pull request that will require changes to be made.

Go to the magit-status buffer again: SPC u SPC g s ~/.emacs.d RET.
Check out your existing fix/spacemacs-home-buffer-bookmarks-jump branch (or whatever it is you named your branch when creating it) by typing b b and then fix/spacemacs-home-buffer-bookmarks-jump.
Make your changes as you did before.
Instead of creating a new commit with the changes, you can amend the existing commit. First type c from the magit-status buffer. Then type a which will open up the same commit buffer as before. Your existing commit message should already be pre-filled in the buffer. You can choose to modify it or commit with the same message by typing C-c C-c as before.

From the command line, type git commit --amend to achieve the same result as above.
It is advised to ensure your fix/spacemacs-home-buffer-bookmarks-jump branch is up-to-date with upstream/develop before updating the pull request. This can be done by typing F in the magit-status buffer, then typing r, followed by e. In the popup that appears, type upstream/develop to rebase your current branch with changes from upstream/develop. This will pull all changes from upstream/develop, first apply them locally, and then apply your most recent commit from the above step on top of it.

From the command line, type git pull --rebase upstream develop for the same result.
Push your changes to origin. Type P, followed by -force, followed by u to push our changes. Note: Since we've updated an existing commit, we need to force push our changes. Otherwise, they will be rejected by Github.

From the command line, type git push -f origin fix/spacemacs-home-buffer-bookmarks-jump for the same result.