New custom-logic action input

[aciceri]

Description

I've added a new option custom-logic that allows executing custom logic after that update-flake-lock.sh is executed but before that the PR body is interpolated. The use case that justified this is that I wanted to put the output of nix store diff-closures inside the PR body. But I couldn't do this before the entire update-flake-lock action since I needed to run it after that the lockfile was updated.

 - name: Update flake.lock
    uses: aciceri/update-flake-lock@main
    with:
      custom-logic: |
        EOF=$(dd if=/dev/urandom bs=15 count=1 status=none | base64)
        echo "DIFF_CLOSURES<<$EOF" >> $GITHUB_ENV
        nix run .#diff-closures >> $GITHUB_ENV
        echo "$EOF" >> $GITHUB_ENV
      pr-title: "Automatic `flake.lock` update"
      pr-body: |
        # Automatic update
        ## Inputs updated
        ```
          {{ env.GIT_COMMIT_MESSAGE }}
        ```
        ## Closures diff
        ```
        {{ env.DIFF_CLOSURES }}
        ```

Frankly I don't know if you want this, perhaps it's just an useless complication that will be useful for a small portion of people. Meanwhile I leave it here as a draft PR and only if you like it I'll add some lines in the README

Checklist

• Tested functionality against a test repository (see "How to test changes") Not the template one but this
• Added or updated relevant documentation (leave unchecked if not applicable)

[grahamc]

Hi @aciceri, we've been discussing this issue internally and think it would be better solved by documentation about how to accomplish this, instead of building support for it in directly. We think that would ultimately better and more flexible for folks. Does that make sense to you?

[aciceri]

@grahamc am I missing something or this isn't accomplishable by using the action as is? At the beginning I've tried looking for a workaround that didn't require me to fork the action but I couldn't (can't remember details but my ideas were really ugly/convoluted, it was easier just rewriting the action). I remind you that I want to execute my custom logic before the PR is created/updated but after that the commit with the updated inputs is created.

[cole-h]

Correct, using only this action in its current state, it is not possible to do what you want.

However, is there a reason why executing the custom logic after the PR is created/updated is unacceptable? I think it would be fairly simple to edit the PR description immediately after it has been submitted, and we could add an example in the README demonstrating that.

Specifically, the create-pull-request action we use exposes the PR number of the created PR (as well as whether the operation that action took), and we re-expose that information. So I can imagine that it would be possible to utilize that with another GitHub Action that accepts a PR number or some other identifying information and change the PR body using that info.

[cole-h]

I did a bit of looking and found a couple actions that might be useful:

• https://github.com/devindford/Append_PR_Comment -- It accepts a head-branch-regex that you could set to update_flake_lock_action (the default branch name for our action; replace with whatever branch name you end up using) and use it that way.
• https://github.com/claudiamatosa/github-action-replace-pr-body -- This one replaces the PR body wholesale, but you could have a separate action that triggers this on PRs with the update_flake_lock_action branch, and then read out the PR body, write it to a file, write whatever else you want, and have that action replace it.

---

Another solution could be to use gh CLI in the action like this:

pr=68 # give the update-flake-lock step an id and use ${{ steps.<ID>.outputs.pull-request-number }} here
gh pr view "$pr" --json body --jq .body > body

cat >> body <<EOF

---

Here is some more stuff that I would like to add
EOF

gh pr edit "$pr" --body-file ./body
rm ./body

or this:

pr=68 # give the update-flake-lock step an id and use ${{ steps.<ID>.outputs.pull-request-number }} here
gh pr view "$pr" --json body --template \
'{{.body}}

---

Here is some more stuff that I would like to add' > body

gh pr edit "$pr" --body-file ./body
rm ./body

[aciceri]

Uh you are right, I couldn't think the simplest solution. The only difference is that this way there will be a time delta where the PR is created but I don't have a complete text body for it (in my case it takes about 40 minutes to build a new Emacs) but this isn't a problem for my use case.

Said this I think you can close this, or, if you prefer, I can change this adding an example doing what you suggest (I believe that having diffs or other tasks like running vulnix could be in the general interest for nix folks).

Thanks :)

[grahamc]

I'm going to close this PR since it is pretty directionally different. If you're up for it, it'd be awesome for you to submit an example to the README. Thanks, @aciceri!