This end-to-end guide will show you how to contribute code to the AMP Project. It covers everything from creating a GitHub account to getting your code reviewed and merged.
This guide is intended for people who don't know much about Git/GitHub and the tools we use to build/test AMP (Node.js, Gulp, etc.). The guide may look long, but it includes a lot of explanation so you can get a better understanding of how things work.
If you're already familiar with Git/GitHub/etc. or you just want to know what commands to type in instead of what they're doing take a look at the much shorter Quick Start Guide.
If you have a question or are unsure about something while following this end-to-end guide, you can get help from the AMP Project community in many ways:
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If you are tackling a Great First Issue or other GitHub issue you can ask a question as a comment on the issue directly. This works particularly well if the question is about how to make progress on that specific issue.
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The #welcome-contributors channel on Slack is a place for new contributors getting up to speed in the AMP Project to find help. You should feel comfortable asking any question in there no matter how basic it may seem to you (e.g. problems getting Git set up, errors during a build, etc.). If you haven't already signed up for our Slack, you'll need to request an invitation.
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You can also ask questions on [email protected].
People who have never used Git or GitHub before can find them intimidating--even people who have been coding on large projects for years. Once you understand a few basic concepts and several commands your day-to-day experience with Git will generally be straightforward.
Despite the similarity in names, Git & GitHub are different:
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Git is a version control system. You'll install the Git client locally and run Git commands to grab code from a Git repository, make changes and submit code. You don't need to use GitHub to use Git, but the AMP Project's Git repository happens to be hosted on GitHub.
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GitHub hosts Git repositories and provides other tools that make managing projects easier (like a GUI for code reviews, bug tracking, etc.).
To contribute to the AMP Project you'll use Git to grab a copy of the code from the amphtml Git repository on GitHub, make changes locally and push your changes back up to your own Git repository on GitHub so you can get your code changes reviewed and merged into the amphtml codebase.
Create a GitHub account if you don't already have one. Because the AMP Project is an open source project you can create a free GitHub account (i.e. click "Join GitHub for free" on the pricing page you end up on). Once your account is created set up two-factor authentication for your account.
After you are done setting up your GitHub account install and set up Git. You'll download and install Git, perform some basic configuration and then set up authentication for talking to GitHub. Although the authentication instructions suggest HTTPS is recommended, you should follow the "Connecting over SSH" instructions instead. SSH is required for two-factor authentication which we recommend you use. (The rest of these instructions will assume you are using SSH.)
One of the central concepts of Git is the repository, where files are stored and kept track of. You can browse the amphtml repository using the GitHub web UI.
The process of getting the amphtml code, making changes, getting your changes reviewed and then having your changes become a part of the AMP Project involves three repositories:
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The first repository is the amphtml repository mentioned above. When you want to fix a bug or add a feature to AMP your goal is to get your code to become part of this repository (merged in Git terms). The amphtml repository is an example of a remote repository because it's stored in a server that your Git client connects to.
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You'll create a fork of the amphtml repository on GitHub before you make your first change. This creates your own complete copy of all of the files from the amphtml repository which gives you a place to put your changes without affecting other people's work. Since your fork is on GitHub's servers this is also a remote repository. Once you create your fork you'll be able to browse a copy of all of the files on the Web UI at
https://github.com/<your username>/amphtml. -
In general you won't be making changes directly on your fork on GitHub since GitHub provides very limited edit and build capabilities. Instead you'll create a copy of your fork in a local repository which will download all of the amphtml files to your computer. This is where you'll typically be building AMP, making changes, testing them out, etc.
If you are new to Git it may seem surprising that there are three different repositories involved but each one serves its purpose. Here's how they interact in a typical scenario:
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You'll make changes on your computer (your local repository).
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When you're done you'll push these changes to your fork on GitHub so that others can see your changes and review them before they become part of the amphtml repository.
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When the changes have been approved by someone with permission to do so that person will handle merging your changes from your GitHub fork to the amphtml repository.
Note that each of these repositories has a complete copy of the entire amphtml codebase. If your local repository is on your computer and you lose your internet connection you'll still be able to make changes to any file in your local repository. Part of the workflow for Git that we'll go through is how you keep these three repositories in sync.
One thing that might put your mind at ease: if you aren't currently a core committer to the amphtml project you can't actually make changes to the amphtml repository directly--so go ahead and try out different Git commands without worrying you're going to break things for other people.
To create your fork on GitHub and your local copy of that fork:
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Create a fork of the amphtml repository on GitHub by going to https://github.com/ampproject/amphtml and clicking the "Fork" button near the top. Your GitHub fork will now be visible at
https://github.com/<your username>/amphtml. -
Create your local copy (or clone) of your fork:
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go to a local directory on your computer where you want to put a copy of the code, e.g.
~/src/ampproject -
run the
git clonecommand using the address for your remote repository (your GitHub fork)git clone [email protected]:<your username>/amphtml.git
(Note that this is the SSH address for your GitHub fork since we assume you've set up SSH for your account as we recommended. You can always find the SSH and HTTPS addresses of your GitHub fork by clicking the "Clone or download" button on your GitHub fork page.)
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After running the command you'll see something like Receiving objects and a progress indicator; this is actually downloading all of the files in the repository to your computer.
Once the clone is done you can browse around your newly created local directories and convince yourself that they're the same as what you see on the remote amphtml repository and on your GitHub fork.
As described in the previous section you have three repositories you are working with. It can be helpful to setup aliases to refer to the remote repositories so you don't have to remember their full addresses. You'll be using these aliases a lot in Git commands.
The git clone command you ran above automatically set up one alias for you. From the local amphtml directory the git clone command created, run
git remote -v
and you will see
origin [email protected]:<your username>/amphtml.git
This indicates that the alias origin can be used to refer to your GitHub fork remote repository.
You should also set an alias for the remote amphtml repository since you'll be referring to that in some Git commands. The convention is to use the alias upstream for this repository. The address for the amphtml repository looks a lot like the address for your GitHub fork except your username is replaced by ampproject.
git remote add upstream [email protected]:ampproject/amphtml.git
Now run git remote -v again and notice that you have set up your upstream alias.
Now that you have all of the files copied locally you can actually build the code and run a local server to try things out.
amphtml uses Node.js, the yarn package manager and the Gulp build system to build amphtml and start up a local server that lets you try out your changes. Installing these and getting amphtml built is straightforward:
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Install NodeJS (which includes npm).
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Install yarn
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In your local repository directory (e.g.
~/src/ampproject/amphtml), install the packages that AMP uses by runningyarnYou should see a progress indicator and some messages scrolling by. You may see some warnings about optional dependencies that are generally safe to ignore.
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For some local testing we refer to fake local URLs in order to simulate referencing third party URLs. This requires extra setup so your browser will know that these URLs actually point to your local server.
You can do this by adding this line to your hosts file (
/etc/hostson Mac or Linux,%SystemRoot%\System32\drivers\etc\hostson Windows):127.0.0.1 ads.localhost iframe.localhost -
The AMP Project uses Gulp as our build system. Gulp uses a configuration file (gulpfile.js) to build amphtml (including the amphtml javascript) and to start up the Node.js server with the proper settings. You don't really have to understand exactly what it is doing at this point--you just have to install it and use it.
You can install Gulp using yarn:
yarn global add gulp
Now whenever you're ready to build amphtml and start up your local server, simply go to your local repository directory and run:
gulp
Running the gulp command will compile the code and start up a Node.js server listening on port 8000. Once you see a message like Finished 'default' you can access the local server in your browser at http://localhost:8000
You can browse the http://localhost:8000/examples directory to see some demo pages for various AMP components and combination of components.
Note that by default each of the pages in the /examples directory actually uses the production version of AMP JavaScript; you can verify this by loading an example page in your browser, viewing the source and seeing that it is loading the AMP JavaScript from cdn.ampproject.org.
For local development you will usually want to load the JS from your local server to test your changes. You can do this by changing the URL suffix from .html to .max.html, e.g.
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http://localhost:8000/examples/article.amp.html loads an example page that uses AMP JS from cdn.ampproject.org
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http://localhost:8000/examples/article.amp.max.html loads an example page that uses the locally built JS (if you view the source of the .max.html files, you'll see that it is loading the JS from your local
/distdirectory)
When you're ready to make changes, you'll want to follow the steps below for creating a branch, testing and sending your changes for review.
The exact changes you'll be making will depend on the issue/feature you are working on. If you aren't sure where to start, ask for suggestions on the GitHub issue tracking the work you are doing or reach out to the community as described in How to get help.
You may have noticed that the files in your local repository are editable which makes it tempting to start making your changes right away. The typical Git workflow, however, takes advantage of one of the best features of Git: branches.
Branches let you work on multiple different things in your repository in parallel. For example you can have one branch where you're fixing a bug, another branch where you're implementing a new feature and yet another branch where you're just doing some exploratory work. These branches co-exist in the same repository so there's no need to go through the forking and cloning steps described earlier every time you want to make a change.
By default you'll have a branch named master. You can see this if you run the command git branch which lists the branches in your local repository.
Although you could do work on the master branch, most people choose to leave the master branch unchanged and create other branches to actually do work in. Creating a branch is easy; simply run:
git branch --track <branch_name> origin/master
Whenever you want to do work in this branch, run the checkout command:
git checkout <branch_name>
You can see a list of your branches and which one you're currently in by running:
git branch
When you created the branch the --track flag and origin/master part are a convenience for telling Git the default place you want to sync with in the future. Remember origin is the alias that was set up for your GitHub fork remote repository. origin/master is "the master branch of the origin repository."
Note that currently the branch you just created only exists in your local repository. If you check the list of branches that exist on your GitHub fork at https://github.com/<your username>/amphtml/branches/yours, you won't see this new branch listed. Later on when we want to make the changes in your branch visible to others (e.g. so you can do a pull request) we'll push this branch to your GitHub fork.
Since your local repository is just a copy of the amphtml repository it can quickly become out of date if other people make changes to the amphtml repository. Before you start making changes you'll want to make sure you have the latest version of the code; you'll also want to do this periodically during development, before sending your code for review, etc.
In the workflow we will be using you'll go to the master branch on your local repository and pull the latest changes in from the remote amphtml repository's master branch. (Remember that you set up the alias upstream to refer to the remote amphtml repository.)
# make sure you are in your local repo's master branch
git checkout master
# pull in the latest changes from the remote amphtml repository
git pull upstream master
If there have been any changes you'll see the details of what changed, otherwise you'll see a message like Already up-to-date.
After running that git pull command your local master branch has the latest files, but your other local branches won't get automatically updated. To get a local branch in sync:
# go to the branch you want to sync
git checkout <branch name>
# bring the latest changes from your master branch into this branch
git rebase master
Since you just ran the git pull in your master branch it has the latest changes from the remote amphtml repository so running git rebase master in your other branch effectively brings the latest changes from the remote amphtml repository to this other branch.
If there are changes that conflict with changes on your branch (e.g. someone modified a file that you're working on) you'll be prompted to resolve them at this point.
The common workflow for making changes to files in Git is:
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edit some files using your favorite editor
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tell Git that you care about these changes by staging them using the
git addcommand -
create a checkpoint (called a commit) that bundles together the changes you've staged by using the
git commitcommand
Git commits bundle together related changes into a logical unit. (If you're familiar with some other source control systems this terminology may make you think that when you create a commit you're "checking in" your code to the amphtml repository; that's not what a Git commit is.)
You can think of a commit as a checkpoint in your branch. It's a good idea to create a commit when you reach a point in your change that you might want to get back to. You will at least have to create a commit before syncing your changes to another repository (i.e. your GitHub fork) and requesting a code review.
Let's walk through creating a commit after editing a file. First, go to the branch you created earlier:
git checkout <branch name>
Edit a file in this branch using your favorite editor. After editing the file, run
git status
and you should see the file you modified in a section that says Changes not staged for commit along with some helpful suggestions for what to do next.
Git knows that there's a modified file, but isn't sure what you want to do with it. (In Git terms, this file is unstaged.) You have to tell Git that this is a change you care about by using the git add command.
git add <filename>
Now run git status again and you'll see the file listed under a Changes to be committed section.
Since you're done with changes to that file, go ahead and create a commit:
git commit -m "<a brief description of your commit>"
Now run git status again, and you'll see the message nothing to commit and your branch is ahead of 'origin/master' by 1 commit.
Note that you can optionally skip using git add commands and just use the git commit -a flag to say "add all of the modified/deleted files to this commit," e.g.
git commit -a -m "<a brief description of your commit>"
Note that you can add changes into an existing commit but that opens up some additional Git concepts that you don't really need to make a contribution.
Before sending your code changes for review, you will want to make sure that all of the existing tests still pass and you may be expected to add/modify some tests as well.
Make sure you are in the branch that has your changes (git branch <branch name>), pull in the latest changes from the remote amphtml repository and then simply run:
gulp test
You'll see some messages about stuff being compiled and then after a short time you will see a new Chrome window open up that says "Karma" at the top. In the window where you ran gulp test, you'll see a bunch of tests scrolling by (Executed NNNN of MMMM) and hopefully a lot of SUCCESS messages.
By default gulp test runs tests on Chrome. Depending on what your tests affect (e.g. if you're fixing a bug in a different browser), you may need to run gulp test --firefox or gulp test --safari to run in other browsers.
If the tests have failed you will need to determine whether the failure is related to your change.
If the failing test looks completely unrelated to your change, it might be due to bad code/tests that have made it into the amphtml repository. You can check the latest amphtml test run on Travis. If it's green (meaning the tests pass) then it's more likely the failure is a problem with your change. If it's red, you can click through to see if the failing tests are the same as the ones you see locally.
Fixing the tests will depend heavily on the change you are making and what tests are failing. If you need help to fix them you can ask on the GitHub issue you're working on or reach out to the community as described in How to get help.
If your change was not already covered by existing tests, you will generally be expected to add some tests that show your new code works correctly and to prevent other people from breaking your code in the future.
The amphtml unit tests use the Mocha framework, the Chai assertion library and the Sinon mocking library. The specifics of the tests you will need to add will vary depending on the issue/feature you are working on. If you are fixing a bug in an existing component there should already be tests in the test directory for that component that you can look at for guidance. For example the amp-video component has tests.
You can run the tests in a single file by running gulp test --files=<file to test>, e.g. for amp-video:
gulp test --files=extensions/amp-youtube/0.1/test/test-amp-youtube.js
Alternatively you can take advantage of a Mocha feature that allows for running only certain tests--describe.only. Simply replace the describe in the Mocha tests you want to run with describe.only and only those tests will be run when you run gulp test. Make sure to remove the .only and run all tests before sending your code for review.
To make running the tests more convenient you can also use the --watch flag in any gulp test command. This will cause the tests you've indicated to automatically be rerun whenever a file is modified.
If you are not sure how to create these tests you can ask on the GitHub issue you're working on or reach out to the community as described in How to get help.
Up to this point you've been making changes in a branch on your local repository. Those changes aren't visible anywhere else--not even your GitHub fork--so if you want other people to see your changes you will need to push your branch to your GitHub fork. This is a necessary step to request a code review (known as a pull request) and to ultimately get your changes added to the amphtml repository.
Before pushing your changes, make sure you have the latest changes in the amphtml repository on your branch by running the commands we described above:
git checkout master
git pull upstream master
git checkout <branch name>
git rebase master
Now push your changes to origin (the alias for your GitHub fork):
git push origin <branch name>
The changes you've made are now visible on GitHub! Go to your fork on GitHub:
https://github.com/<your username>/amphtml
If you recently pushed the branch you will see a message bar at the top that lists your recently pushed branches next to a convenient "Compare & pull request" button.
Instead of using that button take a look at the "Branch" dropdown on the top left. Click it and then select the branch you just pushed. This will take you to your branch on GitHub:
https://github.com/<your username>/amphtml/tree/<branch name>
Browse around and find the file(s) you modified; you'll see that these match the changes you made in your local repository since you ran git push earlier.
If you make further changes in your local repository on the same branch they will not automatically be reflected on your GitHub fork. You will need to create a commit and push your changes again using the same commands as above.
Note that you can edit files in your branch directly on GitHub using the web UI. For simple changes requested in a pull request (e.g. fixing a typo in a comment) this may be okay, but in general it's best to make the changes in your local repository and push them back up to GitHub to avoid confusion.
In order for your changes to become part of the amphtml repository, you will need to get your code reviewed by one of the core committers via a Pull Request (PR). In fact you won't actually merge your code into the amphtml repository directly; once a core committer approves it he or she will handle the merge for you.
Once your code is ready for a review, go to https://github.com/ampproject/amphtml and click on the "Compare & pull request" button on the "recently pushed branches" banner. If that banner isn't visible, go to your GitHub fork at
https://github.com/<username>/amphtml, use the Branch dropdown to select the branch that contains the changes you want reviewed and press the "New pull request" button.
On the "Open a pull request" page, you will see dropdowns at the top indicating the proposed merge. It will look something like:
amproject/amphtml / master … <username>/amphtml / <branch name>
Below this are text boxes where you can provide a title and description for your pull request. Please follow the guidelines in the template for providing a good title and description. Make sure to refer to any Issues that you are fixing (by typing "Issue #" and selecting it from the autocomplete) so that people can see which issue you are fixing and people watching the issue will see that there's a PR for it.
The reviewer should be one of the core committers and ideally someone who is familiar with the change you are making (e.g. someone you've been communicating with through an associated GitHub issue).
When you're done click "Create pull request." This will bring you to your Pull Request page where you can track progress, add comments, etc.
On the Pull Request page you can see that a couple of checks are running:
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the tests are being run on Travis
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the system is verifying that you have signed a CLA (Contributor License Agreement). If this is your first time submitting a Pull Request for the amphtml project you'll need to sign an agreement. (Make sure the email address you use to sign the CLA is the same one that you configured Git with.) See details in the Contributing code documentation.
If you don't hear back from your reviewer within 2 business days, feel free to ping the pull request by adding a comment.
If your reviewer doesn't request any changes from you they may go ahead and merge your changes into amphtml. If they do this you're done since the reviewer will merge your changes for you! Once your code is merged in you can safely delete your branch.
In the likely event that the reviewer has some comments, you'll need to respond to them.
If the reviewer's comments involve changes in your code, you can make changes on the branch in your local repository in the same way you made your changes originally. When you run git commit after making these changes, you'll be creating a new commit. (There are ways to "squash" all of your changes into a single commit, but since you've already shared the previous commit in a pull request it's best to avoid that.)
Remember that the changes you make in your local branch won't actually be visible to anyone (including your PR reviewer) until you push the changes up to your GitHub fork remote repository. You can follow the same steps you followed earlier in the Push your changes to your GitHub fork section.
You can respond to comments in the GitHub UI. When making comments, you will see a button to "Start a Review" which lets you group all of your comments and send them as a group.
You can always get back to your open Pull Requests on GitHub at https://github.com/ampproject/amphtml/pulls/<your username>.
Creating, deleting and moving between branches in Git is cheap. Reusing branches for multiple unrelated changes can lead to a confusing branch history. For these reasons it's best to delete your branch once your PR using that branch has been approved and merged. (It can also be really satisfying to delete a branch after a particularly involved change.)
GitHub offers a convenient "Delete branch" button on the PR page after the changes in your branch have been merged into the amphtml repository. You can click this button to delete your branch in the GitHub fork if you prefer, but you will also want to delete the branch in your local repository:
# go back to the master branch
git checkout master
# delete the branch in your local repository
git branch -D <branch name>
# delete the branch in your GitHub fork (if you didn't use the UI)
git push origin --delete <branch name>
Congratulations on making your first change to AMP!
If your change affected internal documentation, tests, the build process, etc. you can generally see your changes right after they're merged. If your change was to the code that runs on AMP pages across the web you'll have to wait for the change to be included in a release.
In general we cut a release of amphtml on Wednesdays during working hours (Pacific time) and push it to the AMP Dev Channel the next day. After verifying there are no issues, we push that build to 1% of AMP pages the following Monday and complete the push to all AMP pages a few days later on Thursday. That is: on Thursday we will typically push last week's build to all AMP pages and this week's build to the Dev Channel.
Once the push of the build that includes your change is complete all users of AMP will be using the code you contributed!
You can see whether your change made it into a given build on the amphtml Releases page. The build marked Pre-release is the version on the Dev Channel and the build marked Latest Release is what is running in production. Your Pull Request will be listed in the first build that includes it; if you don't see your Pull Request listed it will likely be in the next build.
You can set your browser to use the Dev Channel build by enabling dev-channel on the AMP Experiments page. This will let you see how your changes will affect any AMP page before your changes are rolled out to all AMP pages. Note that this only affects the browser in which you enable the experiment.
You can verify the AMP version your browser is using for a given page by looking at your browser's developer console. After loading an AMP page (e.g. https://ampproject.org) the console will have a message like Powered by AMP ⚡ HTML – Version <build number>). The <build number> will match one of the build numbers on the amphtml Releases page.
The Release Schedule doc has more details on the release process.
Now that you know the process for making changes to the AMP Project you already have most of the heavy lifting done. We look forward to seeing your future contributions to the project. :)
This end-to-end guide provided enough details to get a basic understanding of a typical workflow for contributing code to the AMP Project. If you find yourself wanting to know more there are a lot of resources available. Here are a few:
- GitHub has a lot of helpful introductory material, including:
- a Hello World tutorial that's a bit less in depth than this guide, but it covers things like creating a new repository and merging in code after a pull request
- the Git cheat sheet from GitHub provides a quick reference to some common commands, including many we didn't cover in this guide (such as diff and log)
- a Training & Guides video series
- The official Git docs have a lot of information including the reference docs and an online version of Pro Git.
- You may see discussions about the difference between rebasing and merging in Git, and we glossed over the details in this guide. If you're curious about the difference the Atlassian Merging vs. Rebasing tutorial has a good explanation.