GitHub Multi Comment Action

Combine outputs from many jobs into a single comment

Usage

Create a file named .github/multi-comment.yml to define the section IDs that can appear in the comment.

sections:
  - test_results
  - deploy_preview
  - perf_stats

Now, in your GitHub action workflow, you can run the action with the comment section and message which will be posted.

- name: Comment with test results
  uses: mskelton/multi-comment@v1
  with:
    section: test_results
    message: Hello world

Comment from a file

To comment from a file on disk, you can use the file-path input instead of message.

If both a message and file-path are provided, message will take precedence.

- name: Comment with test results
  uses: mskelton/multi-comment@v1
  with:
    section: test_results
    file-path: /path/to/file.txt

Specifying the pull request

If you are running this action from a workflow without the pull_request context (e.g. workflow_run), you can use the pr-number input to specify which pull request to comment on.

- name: Comment with test results
  uses: mskelton/multi-comment@v1
  with:
    section: test_results
    message: Hello world
    pr-number: 123

Inputs

Action Inputs

Name	Description	Required	Default
section	The section ID that matches with the value in multi-comment.yml	✅
message	Comment body
file-path	File path containing the comment body
pr-number	The pull request number where to create the comment		current pull request number
token	GitHub auth token		${{ github.token }}
config	Path to the config file		.github/multi-comment.yml

Metadata (mutli-comment.yml)

Name	Description	Required
sections	A list of section IDs that defines the order of comment sections	✅
title	An optional title for the comment
intro	An optional introduction for the comment that is displayed under the title

Outputs

Name	Description
id	Comment ID that was created or updated
html_url	URL of the comment that was created or updated

Permissions

Depending on the permissions granted to your token, you may lack some rights. To run successfully, this actions needs at least:

permissions:
  pull-requests: write

How does it work?

I built this action to solve a problem we have at Ramp of lots of CI outputs that each need to post back to the PR via comments. The problem is, the more comments you have, the more noisy it gets.

The idea was, what if you had a single comment that contained everything? Test results, deploy preview URLs, warnings, etc. When you try to build that though, there are some challenges.

First, it should support workflows running in parallel, so the order in which the comments are posted is non deterministic. However, we want the order of sections in the comment to be consistent between runs. Additionally, we need to support updating the comment if you push a new commit, and the test results are now passing instead of failed.

The GitHub issue comments API only supports sending a complete comment body when making updates, so if we just get the current value and send it back with our updates, its possible that two separate jobs update the comment at the same time and one of the updates will be lost. To workaround this, we need a way for jobs to acquire a "lock" on the comment, so that they can safely get the current comment value, make edits, and push the updated value back to GitHub.

What better locking mechanism than reactions! Turns out, the create reaction API will return a 201 Created status when a reaction is newly created and a 200 OK when the reaction already exists. Using this subtle API detail, this action will attempt to acquire a lock by creating the reaction and waiting for a 201 status code. If it receives a 200 status code, it will sleep and retry until it is able to acquire a lock (it will fail after 30 seconds if it fails to acquire a lock). Once the lock is acquired, the existing comment will be downloaded, edited, and pushed back to GitHub. After updating the comment, the lock is released by deleting the reaction.

Simple right? 😉

Thanks

Thanks to thollander/actions-comment-pull-request for the original action this was based on. I have made many changes, but the foundation provided in that action was very helpful!