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**** Contribution Guide

There are many ways to be an open source contributor, and we're here to help you on your way! You may:

  • Raise an issue or feature request in our issue tracker
  • Help another contributor with one of their questions, or a code review
  • Suggest improvements to our Getting Started documentation by supplying a Pull Request
  • Evangelize our work together in conferences, podcasts, and social media spaces.

This guide is for you.

Development Prerequisites

We recommend that you use OrbStack instead of Docker desktop when developing on this project:

brew install orbstack

or OrbStack Website

The tools used by this project are managed by Hermit, a self-bootstrapping package installer. To activate the Hermit environment, cd into the source directory and type:

$ . ./bin/activate-hermit

Tip: Install Hermit's shell hooks to automatically activate Hermit environments when you cd into them.

Once Hermit has been activated you need to install all required dependencies. To do this run:

$ hermit install

If using an IDEA IDE we highly recommend installing the Hermit IDEA plugin. For most other editors, starting your editor from within a terminal in an activated Hermit environment is the best way to ensure the editor's environment variables are correctly set. eg. for VSCode:

$ . ./bin/activate-hermit
$ code .

Once the Hermit environment is activated you can type the following to start a hot-reloading ftl agent:

$ ftl dev ./examples/go

Development processes

Code reviews

Our goal is to maintain velocity while keeping code quality high. To that end, the process is an exercise in trust on the part of the reviewer, and responsibility on the part of the PR author.

In practice, the reviewer will review and approve the PR at the same time, trusting that the author will apply the feedback before merging.

On the author's side, they are responsible for reading and understanding all feedback, and applying that feedback where they think it is appropriate. If either side doesn't understand something and it's important, comment accordingly, or do a quick pairing to resolve it. The author should feel free to re-request a review.

Additional points of note:

  • We discourage bike-shedding. Code and documentation are easy to change, we can always adjust it later.
  • Keep your PRs digestible, large PRs are very difficult to comprehend and review.
  • Changing code is cheap, we can fix it later. The only caveat here is data storage.
  • Reviewing code is everybody's responsibility.

Design process

All of our design documents live in HackMD. Create new design documents from the FTL Design Doc Template.

Many changes are relatively straightforward and don't require a design, but more complex changes should be covered by a design document. Once a DRI (Directly Responsible Individual, a Cash term) is selected, our process for creating and reviewing designs is the following. The DRI:

  1. Does some initial thinking and comes up with a rough approach.
  2. Discuss the design with the team, and particularly the DRI for the subsystem that the change will affect.
  3. If the design seems broadly sound and useful, continue on to write the design doc.
  4. A day or two before the weekly sync, send out the design doc for review.
  5. Address any comments by changing the design or discussion.
  6. Add the design review to the weekly sync meeting. The sync meeting is a good opportunity to discuss the design with the team and address any last feedback.
  7. Once approved by the DRI for that subsystem and the DRI for FTL (if necessary), implement!

Reviewers should avoid bikeshedding.

Of course, feel free to bounce ideas off anyone on the team at any time.

Our design docs are stored in HackMD. There's a template for design docs that should be used. Add a label to your design document, representing its state.

Coding best practices

Optional

We prefer to use types.Optional[T] as opposed to nil pointers for expressing that a value may be missing. This is because pointers are semantically ambiguous and error prone. They can mean, variously: "this value may or may not be present", "this value just happens to be a pointer", or "this value is a pointer because it's mutable". Using a types.Optional[T], even for pointers, expresses the intent much more clearly.

Sum types

We're using a tool called go-check-sumtype, which is basically a hacky way to check that switch statements on certain types are exhaustive. An example of that is schema.Type. The way it works is that if you have a type switch like this:

switch t := t.(type) {
  case *schema.Int:
}

It will detect that the switch isn't exhaustive. However, if you have this:

switch t := t.(type) {
  case *schema.Int:
  default:
    return fmt.Errorf("unsupported type")
}

Then it will assume you're intentionally handling the default case, and won't detect it. Instead, if you panic in the default case rather than returning an error, go-check-sumtype will be able to detect the missing case. A panic is usually what we want anyway, because it isn't a recoverable error.

TL;DR Don't do the above, do this:

switch t := t.(type) {
  case *schema.Int:
    // Handle Int

  // For all cases you don't want to handle, enumerate them with an
  // empty case.
  case *schema.String, *schema.Bool /* etc. */:
    // Do nothing
}

Then when a new case is added to the sum type, go-check-sumtype will detect the missing case statically.

Database and SQL changes

If you make any changes to the sqlc inputs, i.e. all the sql/queries.sql files, the contents of backend/controller/sql/schema, or sqlc.yaml, then you will need to update the Go code that sqlc generates from those inputs:

just build-sqlc

We use dbmate to manage migrations. To create a migration file, run dbmate new with the name of your migration. Example:

dbmate new create_users_table

This will automatically create a migration file in backend/controller/sql/schema/. You can refer to any of the existing files in there as examples while writing your own migration.

This section of the dbmate docs explains how to create a migration if you'd like to learn more.

Controller "services"

Currently all backend logic is contained in the backend/controller package tree. We've started to split functionality out of controller.Service into subpackages, such as backend/controller/pubsub, ibackend/controller/cronjobs, and so on. These packages have the following structure:

controller/
  pubsub/
    internal/dal/... # Data access layer
    internal/sql/... # SQL queries
    service.go

sqlc.yaml is configured to generate code for each of these subpackages using shared types, eg.

- <<: *daldir
  queries:
    - backend/controller/pubsub/internal/sql/queries.sql
    - backend/controller/dal/internal/sql/async_queries.sql
  gen:
    go:
      <<: *gengo
      out: "backend/controller/pubsub/internal/sql"

VSCode extension

The preferred way to develop the FTL VSCode extension is to open a VSCode instance in the frontend/vscode directory. This will load the extension in a new VSCode window. From there, the launch.json and tasks.json files are configured to run the extension in a new window.

Building the extension

just build-extension

Packaging the extension

To package the extension, run:

just package-extension

This will create a .vsix file in the frontend/vscode directory.

Publishing the extension

To publish the extension, run:

just publish-extension

This will publish the extension to the FTL marketplace. This command will require you to have a Personal Access Token (PAT) with the Marketplace scope. You can create a PAT here.

Debugging with Delve

Building with Full Debug Information

To build a binary with full debug information for Delve, use the following command:

FTL_DEBUG=true just build ftl

Debugging a Running Process

For an in-line replacement of ftl dev <args>, use the command:

just debug <args>

This command compiles a binary with debug information, runs ftl dev <args> using this binary, and provides an endpoint to attach a remote debugger at 127.0.0.1:2345. You do not need to run FTL_DEBUG=true just build ftl separately when using this command.

Attaching a Debugger

By running just debug <args> and then attaching a remote debugger, you can debug the FTL infrastructure while running your project.

IntelliJ

Run Debug FTL from the Run/Debug Configurations dropdown while in the FTL project.

VSCode

Run Debug FTL from the Run and Debug dropdown while in the FTL project.

Running OTEL LGTM stack locally

the OTEL LGTM stack consists of the following components:

  • otel collector
  • loki (log storage)
  • grafana (visualization)
  • prometheus metrics db (metrics storage)
  • tempo (tracing storage)

grafana provides a docker image that runs all of these components together intended for development, demo, and testing environments. To run the stack locally:

just observe

This will start the otel-lgtm stack. You can access Grafana at http://localhost:3000. ctrl+c to stop the stack.

Once the observability stack is running, you can start FTL with otel enabled:

just otel-dev

Testing local changes

To use your locally built FTL in a separate project, you can start live rebuild with

just live-rebuild

Then, in a separate terminal, you can use the locally built FTL to test your changes against a separate FTL project by running the locally built FTL from the root of this project:

${FTL_HOME}/build/release/ftl dev

where FTL_HOME is the root of this repository.

Useful links

Communications

Issues

Anyone from the community is welcome (and encouraged!) to raise issues via GitHub Issues.

We have an automated aggregation issue that lists all the PRs and issues people are working on.

Continuous Integration

Build and Test cycles are run on every commit to every branch on GitHub Actions.

Contribution

We review contributions to the codebase via GitHub's Pull Request mechanism. We have the following guidelines to ease your experience and help our leads respond quickly to your valuable work:

  • Start by proposing a change either in Issues (most appropriate for small change requests or bug fixes) or in Discussions (most appropriate for design and architecture considerations, proposing a new feature, or where you'd like insight and feedback)
  • Cultivate consensus around your ideas; the project leads will help you pre-flight how beneficial the proposal might be to the project. Developing early buy-in will help others understand what you're looking to do, and give you a greater chance of your contributions making it into the codebase! No one wants to see work done in an area that's unlikely to be incorporated into the codebase.
  • Fork the repo into your own namespace/remote
  • Work in a dedicated feature branch. Atlassian wrote a great description of this workflow
  • When you're ready to offer your work to the project, first:
  • Squash your commits into a single one (or an appropriate small number of commits), and rebase atop the upstream main branch. This will limit the potential for merge conflicts during review, and helps keep the audit trail clean. A good writeup for how this is done is here, and if you're having trouble - feel free to ask a member or the community for help or leave the commits as-is, and flag that you'd like rebasing assistance in your PR! We're here to support you.
  • Open a PR in the project to bring in the code from your feature branch. We use Conventional Commits, so prefix your PR title with feat:, fix:, or chore: appropriately. feat will result in a minor version bump, and fix will result in a patch version bump.
  • The maintainers noted in the CODEOWNERS file will review your PR and optionally open a discussion about its contents before moving forward.
  • Remain responsive to follow-up questions, be open to making requested changes, and... You're a contributor!
  • And remember to respect everyone in our global development community. Guidelines are established in our CODE_OF_CONDUCT.md.