--changed doesn't grab any files in CI

[Andrew-Chen-Wang]

This is my GitHub Action

      - name: Checkout current branch
        uses: actions/checkout@v4
        with:
          fetch-depth: 1
      - name: Setup Biome
        uses: biomejs/setup-biome@v2
      - name: Check formatting with Biome
        run: biome ci --changed --no-errors-on-unmatched .

---

Here are some local tests

Resulting in this for a PR with 3 commits:

  biome ci --changed --no-errors-on-unmatched .
  shell: /usr/bin/bash -e {0}
Checked 0 files in 65µs. No fixes applied.

When I run locally in a PR branch:

biome ci --changed --no-errors-on-unmatched .
Checked 196 files in 24ms. No fixes applied.

Running without --changed

biome ci --no-errors-on-unmatched .
Checked 213 files in 31ms. No fixes applied.

Curiously, running just check:

npx @biomejs/biome check --no-errors-on-unmatched --files-ignore-unknown=true --write .
Checked 213 files in 37ms. No fixes applied

---

So what's going?

I think --changed requires the main branch to actually be set up. So we could modify the action to look like this:

      - name: Checkout current branch
        uses: actions/checkout@v4
        with:
          fetch-depth: 2
      - name: Checkout main branch
        if: github.event_name == 'pull_request'
        run: git fetch origin main --depth 1
      - name: Setup Biome
        uses: biomejs/setup-biome@v2
      - name: Check formatting with Biome
        run: biome ci --changed --no-errors-on-unmatched .

I wrote a fetch depth of 2 thinking that the 2 commits I have on a PR would compare with the main branch, but, unfortunately, no files were collected.

So there are two bugs in my opinion:

1. There should be some docs documenting how to lint in CI with --changed.
2. I feel like --changed is missing some files. At first I thought "oh maybe it skipped collecting new files", but that doesn't make sense since that's technically a change.

Would love to get some thoughts above:)

For now, I've resolved to not using --changed. When doing type checking in mypy in python land, not checking all files at the same time made us sometimes miss changes, so I worry a linter would have a similar issue due to the sheer nature of git.

Actually this is interesting: I just merged my PR and got this output in both the PR and main branch output

Run biome ci --no-errors-on-unmatched .
Checked 212 files in [4]

But locally, I got

biome ci --no-errors-on-unmatched .
Checked 213 files in 24ms. No fixes applied.

[ematipico]

You're telling git, via Biome, to resolve the changed files from the main branch, as you're checking out the main branch by default.

This is expected.

To solve your issue, you need to tell git, via Biome, to fetch the changed files from the ref of the PR (I am assuming that's what you're setting up, because it isn't stated in the question. Let me know if the intent is different). To do so, there's a --since flag: https://biomejs.dev/guides/integrate-in-vcs/#process-only-changed-files

[Andrew-Chen-Wang]

Yes, I'm looking to perform biome ci check against only changed files. I had already configured "defaultBranch": "main".

To clarify, when I was testing, I was on a PR/feature branch. In the GitHub Action, the checkout action in my first example config checks out the head which is the feature branch. The second example does the same but also performs a git fetch of the main branch; regardless, the ref is always pointed towards the feature branch.

Are you suggesting I write --since=feature-branch?

[Andrew-Chen-Wang]

Just tried adding --since=feature-branch --changed. Still only collected 0 files. Is there an example GitHub Action that biome can provide?

[ematipico]

Did you add origin to the branch?

Something like this should work:

 biome ci --changed --since="origin/${GITHUB_BASE_REF}"

[Andrew-Chen-Wang]

Yea I saw another comment mention that. It also didn't work:

Run biome ci --changed --since="origin/andrew/add-since-for-biome" --no-errors-on-unmatched .
Checked 0 files in 34µs. No fixes applied.

I also tried writing main:

Run biome ci --changed --since="origin/main" --no-errors-on-unmatched .
Checked 0 files in 35µs. No fixes applied.