Compute Files-changed In .taskluster.yml: A GitHub Integration

Hey guys! Let's dive into a challenge I've been tackling with Gecko and the GitHub service – efficiently computing file changes. It's been quite the journey, and I'm excited to share the potential solution we're exploring.

The Gecko Cloning Conundrum

So, the core issue we're facing is that Gecko, being the massive project it is, takes a significant amount of time to clone. To combat this, we've been using shallow clones, which drastically speed things up. However, this introduces a new problem: shallow clones don't play nicely with our current method of computing file changes. Our current approach relies on git merge-base to identify the common ancestor between the head_rev and the default branch (or base_ref if provided). We need this because, despite appearances, GitHub doesn't consistently provide a reliable base revision in its pull request or push webhook events. Trust me, I've been there, staring at the screen, wondering why it's not working as expected!

The problem is that git merge-base and shallow clones are like oil and water. They just don't mix without some extra effort. Trying to use them together means we have to incrementally fetch history until the base is detected. Ironically, this process often takes even longer than a full clone would! Talk about frustrating, right? We are talking about long clone times here, which is unacceptable.

This leaves us with a couple of less-than-ideal options. We could either grin and bear the long clone times, which isn't great for anyone's productivity, or we could ditch git merge-base. The latter would mean our files-changed information might not always be accurate, and that's a compromise we're not willing to make. Accuracy is key, especially when it comes to things like task execution and dependency management.

Enter the GitHub API: A Potential Solution

But fear not, there's a third option on the table! We could leverage the GitHub API to obtain the files-changed information. It's like having a secret weapon in our arsenal. However, like any powerful tool, it comes with its own set of considerations:

1. Rate Limits: We need to be mindful of how many requests we're making to the API to avoid hitting those pesky rate limits. Nobody wants their builds to grind to a halt because we're making too many API calls!
2. Authentication: To bypass rate limits, we'll need to handle authentication. This means securely managing credentials and ensuring we're authorized to access the necessary information.
3. Dependencies: Integrating with the GitHub API means adding dependencies to Taskgraph, which then need to be vendored into Gecko. This adds a bit of complexity to our build process.

It's definitely a viable path, and I was already diving into the implementation when a thought struck me: What if the GitHub service could provide this information directly? Think about it. The whole purpose of the GitHub service is to make interacting with GitHub easier and more convenient. What could be more convenient than having a list of modified files readily available with each event?

Seriously, it feels like a missed opportunity that GitHub doesn't offer an easy way to get this information in the first place. But hey, if we can implement it within the GitHub service, we can at least solve the problem in one central location. This would save Taskcluster consumers from having to reinvent the wheel and figure out their own solutions.

Why This Makes Sense: The GitHub Service Advantage

Let's break down why I believe this approach makes a lot of sense:

1. Authentication is Already Handled: The GitHub service is already authenticated with an app. This means we don't have to worry about managing authentication or hitting rate limits. It's like having a VIP pass to the GitHub API!
2. Octokit is Our Friend: The GitHub service already uses Octokit, which is a fantastic library for interacting with the GitHub API. Octokit provides methods for retrieving files from a pull request and a compare API for pushes. We're essentially building on top of existing infrastructure, which is always a good thing.
3. A Natural Integration Point: There's a clear and logical place to query this information and include it in the .tc.yml render context. This makes it easy for Taskcluster consumers to access the file change information they need.

I'm personally excited about the possibilities this opens up. Imagine being able to easily and reliably determine which files have changed in a commit or pull request. This information can be used to optimize task execution, trigger specific workflows, and gain deeper insights into the impact of code changes. This is the value of files-changed being correct.

Additional benefits of the Github service for file changes

Let's explore the benefits more deeply and make it more persuasive to adopt this approach. By integrating the computation of files-changed directly into the GitHub service, we unlock a range of advantages that extend beyond simply solving the shallow clone problem. This strategic move centralizes the logic, reduces redundancy, and opens doors to new possibilities for task execution and workflow optimization. One of the primary advantages is the centralization of logic. Currently, each Taskcluster consumer potentially needs to implement its own method for determining file changes. This leads to duplicated effort, inconsistencies, and a higher maintenance burden. By embedding this functionality within the GitHub service, we create a single source of truth. Any consumer can reliably access this information without needing to implement its own solution. This not only saves time and resources but also ensures consistency across the board. Speaking of consistency, we want to make sure that all consumers can rely on the files-changed information being accurate and up-to-date, regardless of the specific context or event. This is particularly crucial for tasks that depend on specific files or directories. A centralized approach guarantees that the information is computed in a standardized way, eliminating the risk of discrepancies or errors. We also have to take into account the reduction in maintenance burden. When file change computation is distributed across multiple consumers, updates and bug fixes need to be applied in several places. This increases the risk of overlooking something and can lead to inconsistencies. A centralized solution simplifies maintenance since changes only need to be made in one location. This makes it easier to keep the functionality up-to-date and reliable. A centralized system is simply easier to maintain.

Moreover, let's talk about the performance benefits. The GitHub service is well-positioned to efficiently compute file changes since it has direct access to the GitHub API and the necessary authentication credentials. This allows it to optimize the process and avoid unnecessary overhead. Consumers can then access this information without incurring the cost of making API calls themselves or performing complex Git operations. Consumers are happy, and performance is better!

In addition, we can now enable advanced task execution strategies. Accurate file change information opens the door to more sophisticated task execution strategies. For example, we can selectively trigger tasks based on the files that have been modified. This reduces the number of tasks that need to be run, saving time and resources. Additionally, we can prioritize tasks that are affected by critical changes. This ensures that the most important code is tested and deployed quickly. We are talking about making things more efficient and agile here. If we do not have a way to compute for file changes, we will not be able to execute tasks in an advanced way.

Finally, we can now have better insights and analytics. By tracking file changes at the service level, we can gain valuable insights into development patterns and code dependencies. This information can be used to improve code quality, identify potential bottlenecks, and optimize the development process. For example, we can track which files are most frequently modified, identify areas of the codebase that are particularly complex, and gain a better understanding of how different parts of the system interact. This level of insight would be difficult to achieve if file change computation was distributed across multiple consumers.

Overall, integrating the computation of files-changed into the GitHub service is not just a solution to the shallow clone problem. It's a strategic move that centralizes logic, reduces redundancy, improves performance, enables advanced task execution, and provides valuable insights. By making this change, we can significantly improve the efficiency and effectiveness of our development workflows.

I'm Ready to Roll Up My Sleeves!

I'm personally excited about taking on the implementation work for this. I believe it's a worthwhile investment that will pay off in the long run by streamlining our workflows and making life easier for everyone involved. The benefits of having a reliable and centralized way to compute file changes are substantial, and I'm eager to see this become a reality.

What do you guys think? I'd love to hear your thoughts and feedback on this approach. Let's make this happen!

Learn more about GitHub's API on their official documentation.