Question

Contributing code to PX4

Adding a feature to PX4 follows a defined workflow. In order to share your contributions on PX4, you can follow this example.

• Sign up for github if you haven’t already
• Fork the Firmware (see here)
• Clone your forked repository to your local computer
  

  cd ~/wherever/
  git clone https://github.com/<your git name>/Firmware.git

• Go into the new directory, initialize and update the submodules, and add the original upstream Firmware
  

  cd Firmware
  git submodule update --init --recursive
  git remote add upstream https://github.com/PX4/Firmware.git

• You should have now two remote repositories: One repository is called upstream that points to the PX4 Firmware,
  and one repository that points to your forked repository of the PX4 repository.
• This can be checked with the following command:

  git remote -v

• Make the changes that you want to add to the current master.
• Create a new branch with a meaningful name that represents your feature
  

  git checkout -b <your feature branch name>

  you can use the command git branch to make sure you’re on the right branch.
• Add your changes that you want to be part of the commit by adding the respective files
  

  git add <file name>

  If you prefer having a GUI to add your files see Gitk or git add -p.
• Commit the added files with a meaningful message explaining your changes
  

  git commit -m "<your commit message>"

  For a good commit message, please refer to Contributing section.
• Some time might have passed and the upstream master has changed. PX4 prefers a linear commit history and uses git rebase. To include the newest changes from upstream in your local branch, switch to your master branch
  

  git checkout master

  Then pull the newest commits from upstream master
  

  git pull upstream master

  Now your local master is up to date. Switch back to your feature branch
  

  git checkout <your feature branch name>

  and rebase on your updated master
  

  git rebase master

• Now you can push your local commits to your forked repository
  

  git push origin <your feature branch name>

• You can verify that the push was successful by going to your forked repository in your browser: https://github.com/<your git name>/Firmware.git
  
  There you should see the message that a new branch has been pushed to your forked repository.
• Now it’s time to create a pull request (PR). On the right hand side of the “new branch message” (see one step before), you should see a green button saying “Compare & Create Pull Request”. Then it should list your changes and you can (must) add a meaningful title (in case of a one commit PR, it’s usually the commit message) and message (explain what you did for what reason. Check other pull requests for comparison)
• You’re done! Responsible members of PX4 will now have a look at your contribution and decide if they want to integrate it. Check if they have questions on your changes every once in a while.

Update Submodule

There are several ways to update a submodule. Either you clone the repository or you go in the submodule directory and follow the same procedure as in Contributing code to PX4.

Do a PR for a submodule update

This is required after you have done a PR for a submodule X repository and the bug-fix / feature-add is in the current master of submodule X. Since the Firmware still points to a commit before your update, a submodule pull request is required such that the submodule used by the Firmware points to the newest commit.

cd Firmware

• Make a new branch that describes the fix / feature for the submodule update:

  git checkout -b pr-some-fix

• Go to submodule subdirectory

  cd <path to submodule>

• PX4 submodule might not necessarily point to the newest commit. Therefore, first checkout master and pull the newest upstream code.

  git checkout master
  git pull origin master

• Go back to Firmware directory, and as usual add, commit and push the changes.

  cd -
  git add <path to submodule>
  git commit -m "Update submodule to include ..."
  git push upstream pr-some-fix

Checkout pull requests

You can test someone’s pull request (changes are not yet merged) even if the branch to merge only exists on the fork from that person. Do the following

git fetch upstream  pull/<PR ID>/head:<branch name>

PR ID is the number right next to the PR’s title (without the #) and the <branch name> can also be found right below the PR ID, e.g. <the other persons git name>:<branch name>. After that you can see the newly created branch locally with

git branch

Then switch to that branch

git checkout <branch name>

Common pitfalls

Force push to forked repository

After having done the first PR, people from the PX4 community will review your changes. In most cases this means that you have to fix your local branch according to the review. After changing the files locally, the feature branch needs to be rebased again with the most recent upstream/master. However, after the rebase, it is no longer possible to push the feature branch to your forked repository directly, but instead you need to use a force push:

git push --force-with-lease origin <your feature branch name>

Rebase merge conflicts

If a conflict occurs during a git rebase, please refer to this guide.

Pull merge conflicts

If a conflict occurs during a git pull, please refer to this guide.