.github/workflows/size-diff.yml

# Calculates the size diffs for the each example binary. Runs when a pull
# request is created or modified.

name: size-diff

# We want to run this on all pull requests. Additionally, Bors needs workflows
# to run on the `staging` and `trying` branches to block merges on them.
on:
  pull_request:
  push:
    branches:
      - staging
      - trying

jobs:
  size-diff:
    # Using ubuntu-latest can cause breakage when ubuntu-latest is updated to
    # point at a new Ubuntu version. Instead, explicitly specify the version, so
    # we can update when we need to. This *could* break if we don't update it
    # until support for 18.04 is dropped, but it is likely we'll have a reason
    # to update to a newer Ubuntu before then anyway.
    runs-on: ubuntu-18.04

    steps:
      # Clones a single commit from the libtock-rs repository. The commit cloned
      # is a merge commit between the PR's target branch and the PR's source.
      # We'll later add another commit (the pre-merge target branch) to the
      # repository.
      - name: Clone repository
        uses: actions/checkout@v2.3.0

      # The main diff script. Stores the sizes of the example binaries for both
      # the merge commit and the target branch. We display the diff in a
      # separate step to make it easy to navigate to in the GitHub Actions UI.
      #
      # If the build on master doesn't work (`make -j2 examples` fails), we
      # output a warning message and ignore the error. Ignoring the error
      # prevents this workflow from blocking PRs that fix a broken build in
      # master.
      - name: Compute sizes
        run: |
          UPSTREAM_REMOTE_NAME="${UPSTREAM_REMOTE_NAME:-origin}"
          GITHUB_BASE_REF="${GITHUB_BASE_REF:-master}"
          cd "${GITHUB_WORKSPACE}"
          make -j2 examples  # The VM this runs on has 2 logical cores.
          cargo run --release -p print_sizes >'${{runner.temp}}/merge-sizes'
          git remote set-branches "${UPSTREAM_REMOTE_NAME}" "${GITHUB_BASE_REF}"
          git fetch --depth=1 "${UPSTREAM_REMOTE_NAME}" "${GITHUB_BASE_REF}"
          git checkout "${UPSTREAM_REMOTE_NAME}/${GITHUB_BASE_REF}"
          make -j2 examples && \
            cargo run --release -p print_sizes >'${{runner.temp}}/base-sizes' || \
            echo 'Broken build on the master branch.'

      # Computes and displays the size diff. diff returns a nonzero status code
      # if the files differ, and GitHub interprets a nonzero status code as an
      # error. To avoid GitHub interpreting a difference as an error, we add
      # || exit 0 to the command. This also prevents the workflow from failing
      # if the master build is broken and we didn't generate base-sizes.
      - name: Size diff
        run: diff '${{runner.temp}}/base-sizes' '${{runner.temp}}/merge-sizes' || exit 0