Setting created_at with GitHub Actions when a PR is merged

The blog that you’re reading is a static site that’s generated on every push to main. That means that whatever’s in the repo is the source of truth, including the created_at date when a PR is merged.

I do a lot of my writing in batches, but don’t want to publish everything at the same time. Rather than keeping finished posts in Ulysses (my writing app of choice) and staging a new post every time I want to publish, I raise a pull request immediately and use GitHub Actions to set the created_at date when publishing a post.

Here’s the rough workflow:

• Check if the submit-post label has been added
• Fetch the list of changed files in the PR
• For each added file, fetch the file contents
• Replace the created_at date (it’s called date in the frontmatter) in each file (using .replace() but I should probably use gray-matter)
• Use github.repos.createOrUpdateFileContents to update the contents of each file
• Use github.pulls.merge with merge_method: "squash" to merge the PR as a single commit (createOrUpdateFileContents adds multiple commits)
• Delete the branch

I could write a new GitHub Action to do this, but as it’s not reusable and it’s only a small number of lines I’ve chosen to use actions/github-script which lets me write JavaScript and use the GitHub API easily.

js
on:
  pull_request:
    types:
      - labeled
jobs:
  merge-label:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/github-script@v4
        id: set-result
        with:
          github-token: $
          script: |
            const labelName = context.payload.label.name;
            if (labelName != "submit-post"){
              console.log(`${labelName} label was added. No action needed`);
              return;
            }
            const {data: files} = await github.pulls.listFiles({
              pull_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
            });
            // Load all new files + their contents
            const newPosts = await Promise.all(files.filter(f => {
              return f.status == 'added' && f.filename.endsWith(".md")
            }).map(async f => {
              const blob = await github.request(`GET ${f.contents_url}`);
              const content = Buffer.from(blob.data.content, 'base64').toString();
              return {sha: f.sha, filename: f.filename, content};
            }));
            // Replace the date + updated_at with the current date
            const now = (new Date).toISOString();
            await Promise.all(newPosts.map(async f => {
              f.content = f.content.replace(/date: "[^"]+"/mi, `date: "${now}"`);
              f.content = f.content.replace(/updated_at: "[^"]+"/mi, `updated_at: "${now}"`);
              return await github.repos.createOrUpdateFileContents({
                owner: context.repo.owner,
                repo: context.repo.repo,
                path: f.filename,
                message: "Update date",
                branch: context.payload.pull_request.head.ref,
                sha: f.sha,
                content: Buffer.from(f.content).toString('base64'),
                committer: {
                  name: "Michael Heap",
                  email: "[email protected]"
                }
              });
            }));
            // Wait 10 seconds for changes to propogate
            await new Promise((resolve) => {
              setTimeout(resolve, 10000);
            });
            // Squash and merge the PR
            await github.pulls.merge({
              pull_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              merge_method: "squash"
            });
            // Delete the branch
            github.git.deleteRef({
              repo: context.repo.repo,
              owner: context.repo.owner,
              ref: `heads/${context.payload.pull_request.head.ref}`
            });
          result-encoding: string

This action allows me to stage posts when I finish writing them rather than when I plan to publish. Once my intended publishing date arrives, I add the submit-post label to the PR (usually via my phone) and the post is published as intended.