pr-size.yml

name: PR Size Check and Label

# Uses pull_request_target so it works on fork PRs (write access to labels).
# Safe because this workflow only reads PR metadata — it never checks out untrusted code.
on:
  pull_request_target:
    branches: [main]

jobs:
  label-size:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
    steps:
      - name: Calculate PR size and apply label
        uses: actions/github-script@v8
        with:
          script: |
            const prNumber = context.payload.pull_request.number;
            const { owner, repo } = context.repo;

            // Fetch file-level stats so we can exclude generated/lock files
            const files = await github.paginate(github.rest.pulls.listFiles, {
              owner,
              repo,
              pull_number: prNumber,
              per_page: 100
            });

            const EXCLUDED = [
              /package-lock\.json$/,
              /yarn\.lock$/,
              /pnpm-lock\.yaml$/,
              /\.snap$/
            ];

            let additions = 0;
            let deletions = 0;
            for (const file of files) {
              if (EXCLUDED.some(re => re.test(file.filename))) continue;
              additions += file.additions;
              deletions += file.deletions;
            }
            const totalChanges = additions + deletions;

            // Remove existing size labels (catch 404 in case of race)
            const labels = await github.rest.issues.listLabelsOnIssue({
              owner, repo, issue_number: prNumber
            });

            for (const label of labels.data) {
              if (label.name.startsWith('size/')) {
                try {
                  await github.rest.issues.removeLabel({
                    owner, repo, issue_number: prNumber, name: label.name
                  });
                } catch (e) {
                  if (e.status !== 404) throw e;
                }
              }
            }

            // Determine size label
            let sizeLabel;
            if (totalChanges <= 20) sizeLabel = 'size/xs';
            else if (totalChanges <= 100) sizeLabel = 'size/s';
            else if (totalChanges <= 500) sizeLabel = 'size/m';
            else if (totalChanges <= 1000) sizeLabel = 'size/l';
            else sizeLabel = 'size/xl';

            // Ensure the label exists before applying it
            const LABEL_COLORS = {
              'size/xs': '3CBF00',
              'size/s':  '5D9801',
              'size/m':  'FBCA04',
              'size/l':  'E67409',
              'size/xl': 'D93F0B'
            };

            try {
              await github.rest.issues.getLabel({ owner, repo, name: sizeLabel });
            } catch (e) {
              if (e.status === 404) {
                await github.rest.issues.createLabel({
                  owner, repo,
                  name: sizeLabel,
                  color: LABEL_COLORS[sizeLabel],
                  description: `PR size: ${sizeLabel.split('/')[1].toUpperCase()}`
                });
              } else {
                throw e;
              }
            }

            await github.rest.issues.addLabels({
              owner, repo, issue_number: prNumber, labels: [sizeLabel]
            });

            core.info(`PR has ${totalChanges} changed lines (excluding lockfiles/snapshots) → ${sizeLabel}`);

            if (sizeLabel === 'size/xl') {
              core.warning(`PR is large (${totalChanges} lines). Consider splitting into smaller PRs.`);
            }