Pre-requisites:

• Testing is setup

rustfmt is the standard tool for automating code formatting. You can run it manually to clean up your code, integrate it into your text editor to do it automatically, or have it verify if your code is formatted correctly. That last role is what we want to leverage to reduce reduce the burden of handling PRs.

See also example-rustfmt.

We recommend you use the default style as that will be most universal within the Rust ecosystem.

With that said, it would be beneficial to capture a snapshot of that style.

• If users are on different versions of rustfmt with different defaults, it will help minimize conflicts.
• If a new rustfmt is released with a new default, this could cause PRs to start failing, frustrating contributors.

You can lock down your style by running:

rustfmt --dump-default-config .rustfmt.toml

Unlike your tests, there is little value in running more than one job to check the style. We recommend running it on Travis rather than Appveyor because Travis supports your jobs running in parallel.

We'll be adding the following to your .travis.yml:

matrix:
  include:
  - env: RUSTFMT
    rust: 1.24.0  # `stable`: Locking down for consistent behavior
    install:
    - rustup component add rustfmt-preview
    script:
    - cargo fmt -- --write-mode=diff

Highlights:

• matrix: include: is allowing us to define a complete one-off build job.
  • This will run in parallel to your tests, giving you quicker feedback.
  • No other job output will be in here, making it easier to see the results.
• rust: 1.24.0: We run a specific version of Rust to get its version of rustfmt
  • Locking down to a specific version is helpful to avoid behavior changes, even if bug fixes, from breaking PRs.
• env: RUSTFMT: This is purely here because Travis will put it in the job summary, making it easier to distinguish this job from others