check-binary-size.yml

# This workflow checks if a PR commit has changed the size of a hello world Rust program.
# It downloads Rustc and compiles two versions of a stage0 compiler - one using the base commit
# of the PR, and one using the latest commit in the PR.
# If the size of the hello world program has changed, it posts a comment to the PR.
name: Check binary size

on:
  pull_request_target:
    # HACK(jubilee): something broke the distributed LLVM libso and I don't know what.
    branches: []
#      - master

# Both the "measure" and "report" jobs need to know this.
env:
  SIZE_DATA_DIR: sizes

# Responsibility is divided between two jobs "measure" and "report", so that the
# job that builds (and potentnially runs) untrusted code does not have PR write
# permission, and vice-versa.
jobs:
  measure:
    name: Check binary size
    strategy:
      matrix:
        # FIXME(jubilee): the immutable upload needs us to disambiguate things
        # platform: [ubuntu-latest, windows-latest]
        platform: [ubuntu-latest]
    runs-on: ${{ matrix.platform }}
    permissions:
      contents: read
    env:
      # This cannot be used as a context variable in the 'uses' key later. If it
      # changes, update those steps too.
      BACKTRACE_DIR: backtrace
      RUSTC_DIR: rustc
      TEST_MAIN_RS: foo.rs
      BASE_COMMIT: ${{ github.event.pull_request.base.sha }}
      HEAD_COMMIT: ${{ github.event.pull_request.head.sha }}
      SIZE_DATA_FILE: size-${{ strategy.job-index }}.json
    steps:
      - name: Print info
        shell: bash
        run: |
          echo "Current SHA: $HEAD_COMMIT"
          echo "Base SHA: $BASE_COMMIT"
      # Note: the backtrace source that's cloned here is NOT the version to be
      # patched in to std. It's cloned here to access the Github action for
      # building and measuring the test binary.
      - name: Clone backtrace to access Github action
        uses: actions/checkout@v4
        with:
          path: ${{ env.BACKTRACE_DIR }}
      - name: Clone Rustc
        uses: actions/checkout@v4
        with:
          repository: rust-lang/rust
          path: ${{ env.RUSTC_DIR }}
      - name: Set up std repository and backtrace submodule for size test
        shell: bash
        working-directory: ${{ env.RUSTC_DIR }}
        env:
          PR_SOURCE_REPO: ${{ github.event.pull_request.head.repo.full_name }}
        run: |
          # Bootstrap config
          cat <<EOF > config.toml
          change-id = 9999999
          [llvm]
          download-ci-llvm = true
          [rust]
          incremental = false
          EOF

          # Test program source
          cat <<EOF > $TEST_MAIN_RS
          fn main() {
            panic!();
          }
          EOF

          git submodule update --init library/backtrace

          cd library/backtrace
          git remote add head-pr "https://github.com/$PR_SOURCE_REPO"
          git fetch --all
      - name: Build binary with base version of backtrace
        uses: ./backtrace/.github/actions/build-with-patched-std
        with:
          backtrace-commit: ${{ env.BASE_COMMIT }}
          main-rs: ${{ env.TEST_MAIN_RS }}
          rustc-dir: ${{ env.RUSTC_DIR }}
        id: size-reference
      - name: Build binary with PR version of backtrace
        uses: ./backtrace/.github/actions/build-with-patched-std
        with:
          backtrace-commit: ${{ env.HEAD_COMMIT }}
          main-rs: ${{ env.TEST_MAIN_RS }}
          rustc-dir: ${{ env.RUSTC_DIR }}
        id: size-updated
      # There is no built-in way to "collect" all the outputs of a set of jobs
      # run with a matrix strategy. Subsequent jobs that have a "needs"
      # dependency on this one will be run once, when the last matrix job is
      # run. Appending data to a single file within a matrix is subject to race
      # conditions. So we write the size data to files with distinct names
      # generated from the job index.
      - name: Write sizes to file
        uses: actions/github-script@v6
        env:
          SIZE_REFERENCE: ${{ steps.size-reference.outputs.test-binary-size }}
          SIZE_UPDATED: ${{ steps.size-updated.outputs.test-binary-size }}
          PLATFORM: ${{ matrix.platform }}
        with:
          script: |
            const fs = require("fs");
            const path = require("path");

            fs.mkdirSync(process.env.SIZE_DATA_DIR, {recursive: true});

            const output_data = JSON.stringify({
              platform: process.env.PLATFORM,
              reference: process.env.SIZE_REFERENCE,
              updated: process.env.SIZE_UPDATED,
            });

            // The "wx" flag makes this fail if the file exists, which we want,
            // because there should be no collisions.
            fs.writeFileSync(
              path.join(process.env.SIZE_DATA_DIR, process.env.SIZE_DATA_FILE),
              output_data,
              { flag: "wx" },
            );
      - name: Upload size data
        uses: actions/upload-artifact@v4
        with:
          name: size-files
          path: ${{ env.SIZE_DATA_DIR }}/${{ env.SIZE_DATA_FILE }}
          retention-days: 1
          if-no-files-found: error
  report:
    name: Report binary size changes
    runs-on: ubuntu-latest
    needs: measure
    permissions:
      pull-requests: write
    steps:
      # Clone backtrace to access Github composite actions to report size.
      - uses: actions/checkout@v4
      - name: Download size data
        uses: actions/download-artifact@v4
        with:
          name: size-files
          path: ${{ env.SIZE_DATA_DIR }}
      - name: Analyze and report size changes
        uses: ./.github/actions/report-code-size-changes
        with:
          data-directory: ${{ env.SIZE_DATA_DIR }}