Contributing to Piwik with Git

Getting a copy of Piwik to work on

Before you can start contributing you need to get setup with git & github. First, get a github account here. Then login and…

Fork the Piwik repository

While logged in, visit Piwik’s github repo. In the upper right corner there will be a Fork button. Click it. Github will copy the repository and place the new forked repository in your account.

Setup git

When committing, git will need to know your username & email. To set them, run the following commands:

git config --global user.name $username
git config --global user.email $email

Also, if you have a favorite text editor you’d like to use when creating commit messages, you can configure git to launch it when you commit changes. For example:

git config --global core.editor my-text-editor

Clone the forked repository

To be able to work on Piwik you’ll need to have a copy of your forked repository on your computer. To copy your forked repository, run the following command after replacing myusername with your github username:

git clone https://github.com/myusername/piwik piwik

This will copy the entire forked repository (including all history) to the piwik folder on your hard drive.

Now, we’ll run one more command so git remembers the original Piwik repository in addition to your fork:

git remote add upstream https://github.com/piwik/piwik

This will save https://github.com/piwik/piwik as a remote and name it upstream.

Hacking Piwik

Now that you have a copy of the latest Piwik source code, you can start modifying it. For this section, let’s assume there’s a bug that you found and want to fix.

Create a new branch

Before you start coding, you should make sure to keep your changes separate from the master branch. This will make it much easier to track the changes specific to your feature since your changes won’t be mixed with any of your other changes or new commits to the master branch from other developers.

We’ll give our new branch a name, bugfix, that describes what we’re doing so we can recognize it later. To add a new branch, run the following command:

git checkout -b bugfix

The checkout command will create a new branch if the -b option is supplied, otherwise it will try and load an existing branch.

Work on feature

Once you’ve created a branch, you have a place to start working on the feature. There’s nothing special about this part of the process, just fix the bug or finish the feature you’re working on.

If you’re working on something more complex than a bugfix, though, you may have the need to keep your new branch updated with changes from the main repository. Keeping your branch up to date is a two-three step process. First, on your master branch (remember to use the checkout command to switch branches), pull changes from the main Piwik repository, nicknamed upstream:

git pull upstream master

Then, on your new branch (bugfix for this tutorial), merge with master:

git merge master

If there are conflicts, git will list them and tell you to fix them and then commit. To fix commits, you can do it manually in a text editor (which is usually pretty simple), or you can let git launch a GUI by calling:

git mergetool

What git will launch depends on what diff-ing tools you have installed.

After you fix conflicts, you have to let git know the conflicts are gone and re-commit. To do that, you run git add on the files with conflicts then git commit. More on how to add files and commit in the next section.

Save your changes

Now that you’ve finished the bug fix or new feature (or just part of it), it’s time to save your changes. First, you want to commit them to your local clone of your github repository. To do that, run the following command:

git commit -a -m "Fixed a bug."

This will commit every modified file and use “Fixed a bug.” as the commit message. If you have new files to add, run the following command before committing:

git add /path/to/file

If you only want to commit some files and not every modified file, run the above command for every modified file you want to commit, then run:

git commit -m "..."

The -a option (which we used above) tells git to automatically commit every file that has been modified, not just the specific files that have been used with git add.

If you delete a file, git will notice it is deleted, but you still have to git add the file or use the -a option to commit the deletion.

Publish your changes

Now that you’ve committed your changes locally, you need to make them visible on your github repository. This is done with one command:

git push origin bugfix

This command will push every change you made on the bugfix branch to the origin remote (which is your github repository).

You can also use this command to publish changes to your master branch by running:

git push origin master

Create pull request & wait for someone to review the code

Your changes are published, which means you can now send a pull request to the main Piwik project. To do this, visit your forked repository in a browser, and select the bugfix branch in the branch selector (located right above the directory listing on the left side of the page). Then click the Pull Request button in the middle of the top of the page.

On this screen you’ll be able to see exactly what changes you’ve made by looking at your commits and at what files have been changed. You can use this as an opportunity to review your own code if you like.

Once you’re ready to create the pull request, write a description of the pull request and any notes that are important for the person who will review your code, and then click Send pull request. This will create a new pull request which you will be able to find and view here.

Based on the review, make changes & push those changes

Once your pull request is public, someone will review it and leave comments regarding what should be changed. You can then make changes, commit them and then push them to your remote repository (origin) and they will automatically be shown in the pull request.

Once your pull request has been merged, sync w/ master

Your pull request has been reviewed and deemed worthy: it has been merged with Piwik’s master branch. Now, you need to sync your fork with the main repo. This is the same process that was described in Work on Feature:

# first make sure you're on master
git checkout master

# now we'll pull in changes from 'upstream' the original Piwik repository
git pull upstream master

# then we'll push those changes to 'origin'
git push origin master

And finally, now that the changes are part of Piwik, there’s no need for your feature branch, so we’ll delete it:

git branch -D bugfix

Appendix: List of useful commands

• List all branches

  git branch

• Create a new branch:

  git checkout -b $branch_name

• Checkout an existing branch:

  git checkout $branch_name

• Delete existing branch:

  git branch -D $branch_name

• Delete branch in remote repository

  # first delete the branch locally
  git branch -D $branch_name
  
  # then delete the remote branch by running this:
  git push $remote_name :$branch_name

• Revert all changes that haven’t been committed:

  git reset --hard

• Revert changes to one specific file:

  git checkout -- path/to/file

• Commit all modified files + all git added files:

  git commit -a -m "commit message goes here"

  -m is optional.

• Add specific changes and commit only those changes:

  git add path/to/new/file
  git add path/to/deleted/file
  git add path/to/modified/file
  git commit -m "Added new file, deleted old file & modified existing file."

• See status of all files:

  git status

• See log of all commits:

  git log

• Revert commit:

  git revert $commit_hash

  You can get a commit hash by looking through the commit log.

  Note: reverting changes through the command can sometimes get complicated, especially if you’re reverting a merge.

• Push changes to remote:

  git push $remote_name $branch_name

• Pull changes from remote:

  git pull $remote_name $branch_name

• Merge a branch with the currently checked out branch:

  git merge $other_branch

• Merge a branch but make it look like one commit:

  git merge --squash $other_branch
  
  git commit
  
  # in the editor, rewrite the commit message