Action examples

Pull requests

Compare from the merge base — the commit the branch was actually cut from:

name: PR
on:
  pull_request:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Merge base
        id: base
        run: echo "sha=$(git merge-base origin/${{ github.base_ref }} HEAD)" >> "$GITHUB_OUTPUT"

      - uses: leonardochaia/dotnet-affected-action@v7
        id: affected
        with:
          from: ${{ steps.base.outputs.sha }}

      - name: Restore
        if: success() && steps.affected.outputs.affected != ''
        run: dotnet restore affected.proj

      - name: Build
        if: success() && steps.affected.outputs.affected != ''
        run: dotnet build --configuration Release --no-restore affected.proj

      - name: Test
        if: success() && steps.affected.outputs.affected != ''
        run: dotnet test --no-restore --verbosity normal affected.proj

Not the base branch’s tip. github.event.pull_request.base.sha is the tip at the time the PR was opened; if the base branch has moved since, comparing from it sweeps in every unrelated commit that landed in the meantime.

Branch builds

For a branch there is no obvious baseline, so use the last commit that built successfully. A build covers a push rather than a commit, and previous builds may have failed, so the baseline has to reach further back than “the previous commit”.

name: CI
on:
  push:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: nrwl/last-successful-commit-action@v1
        id: last_successful_commit
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          branch: ${{ github.ref_name }}
          workflow_id: 'ci.yml'

      - uses: leonardochaia/dotnet-affected-action@v7
        id: affected
        with:
          from: ${{ steps.last_successful_commit.outputs.commit_hash }}

      - name: Test
        if: success() && steps.affected.outputs.affected != ''
        run: dotnet test affected.proj

nrwl/last-successful-commit-action explains the problem it solves. nrwl/nx-set-shas covers both cases in one step, exposing base and head outputs — use its base as from, and ignore head, since the workspace is already checked out at it.

Picking a specific tool version

- uses: leonardochaia/dotnet-affected-action@v7
  with:
    toolVersion: '7.0.1'

The input takes NuGet range syntax, so '7.*' pins the major while following patches. Pinning an exact version makes CI reproducible; pinning a different major than the action targets will be refused.

Narrowing what is analysed

- uses: leonardochaia/dotnet-affected-action@v7
  id: affected
  with:
    from: ${{ steps.base.outputs.sha }}
    filter-file-path: src/MySolution.slnx
    exclude-output: '\.Benchmarks\.csproj$'
    exclude-discovery: '/legacy/'

--repository-path is always passed and defaults to the workspace, so a filter file in a subdirectory still resolves against the git root and the output still lands where the action reads it back from.

Producing a solution filter

- uses: leonardochaia/dotnet-affected-action@v7
  id: affected
  with:
    from: ${{ steps.base.outputs.sha }}
    filter-file-path: MySolution.sln
    output-format: text slnf

slnf needs a solution to reference, so it goes together with filter-file-path. Keep text in the list — the affected output is read from affected.txt, and without it every run looks like nothing was affected.

Including uncommitted work

The action compares the commits alone whenever from is set, so steps that generate or stamp files before it run cannot change the result. Override it when you want the working tree counted:

- uses: leonardochaia/dotnet-affected-action@v7
  with:
    from: origin/main
    uncommitted: all

Using a matrix

Run the analysis once and let every matrix leg read the same output:

jobs:
  affected:
    runs-on: ubuntu-latest
    outputs:
      affected: ${{ steps.affected.outputs.affected }}
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0
      - uses: leonardochaia/dotnet-affected-action@v7
        id: affected
        with:
          from: origin/main
      - uses: actions/upload-artifact@v4
        if: steps.affected.outputs.affected != ''
        with:
          name: affected
          path: affected.proj

  test:
    needs: affected
    if: needs.affected.outputs.affected != ''
    runs-on: ${{ matrix.os }}
    strategy:
      matrix:
        os: [ubuntu-latest, windows-latest]
    steps:
      - uses: actions/checkout@v4
      - uses: actions/download-artifact@v4
        with:
          name: affected
      - run: dotnet test affected.proj

Caution

affected.proj contains absolute paths, so passing it between jobs only works when the workspace path is the same on both runners. Across operating systems it is not — regenerate per leg, or use the affected output as a list and build the paths yourself.