ci: Use ${GITHUB_BASE_REF} as treeish for checking API break

[simonjbeaumont]

Motivation:

This repo is providing a reusable workflow for checking API breaks but it has two shortcomings:

1. It presumes the target branch name for the PR to be main.
2. It presumes the remote is named origin.

(2) is always the case in CI, but isn't always locally. My remote is named upstream so cannot run this using act. (1) is worse, because it's not actually testing against the target branch of the PR—consider if someone was enabling this reusable workflow on a feature branch or other-named branch.

Fortunately, Github Actions makes the target ref of the pull request available in the GITHUB_BASE_REF environment variable¹.

Modifications:

Use GITHUB_BASE_REF as the argument to swift package diagnose-api-breaking-changes.

Result:

This can now be run locally.

Footnotes

1. https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/store-information-in-variables#default-environment-variables ↩

[rnro]

Looks great!

[FranzBusch]

If I run this locally now without passing the env it will fail right? Can we make the default ref for local act runs main?

[rnro]

If I run this locally now without passing the env it will fail right? Can we make the default ref for local act runs main?

Ah, I had assumed that act took care of setting up the environment for you. I agree that if it doesn't we should have a default.

It says "the environment variables" are set up in the README https://github.com/nektos/act?tab=readme-ov-file#how-does-it-work and GITHUB_BASE_REF is mentioned in the source so it might work

[simonjbeaumont]

If I run this locally now without passing the env it will fail right? Can we make the default ref for local act runs main?

I don't think so. Did it actually fail for you? When I run it without setting it, it works fine.

Ah, I had assumed that act took care of setting up the environment for you. I agree that if it doesn't we should have a default.

No default is required.

Defaulting the ref is a bad thing IMO. By defaulting it to main you are presuming the target branch of the PR, when it isn't explicitly set. When it isn't set, I would expect the best choice for default would be the default branch of the repo. Which you can get by just using nothing:

❯ git fetch https://github.com/apple/swift-nio :one

❯ git fetch https://github.com/apple/swift-nio main:two

❯ git rev-parse one
1851ae6e7d49860ea42e8ba9c4cf0aee9633d524

❯ git rev-parse two
1851ae6e7d49860ea42e8ba9c4cf0aee9633d524