GitHub Action error: "Top level 'runs:' section is required" - github-actions

Question

I am trying to get a private GitHub action to work within my private GitHub org. The private repo that contains these workflow 'templates' has this simple file structure as I'm just trying to get the bare minimum to work:
.
├── .git
├── test
│ ├── action.yml
And the action.yml file contents are:
name: Test
on: push
jobs:
test:
name: Test
runs-on: ubuntu-latest
steps:
- name: Echo
run: |
echo Heyyyyy
I am trying to use this action in another private repo with a workflow file with these contents:
name: Test
on:
push:
branches:
- master
jobs:
test:
name: Test
runs-on: ubuntu-latest
steps:
- uses: actions/checkout#v2
with:
repository: <private-actions-repo>
token: ${{ secrets.REPO_TOKEN }}
path: github-actions
- name: Test private action
uses: ./github-actions/test
When this action runs, I get the following error:
##[error]Top level 'runs:' section is required for /home/runner/work/<private-repo>/./github-actions/test/action.yaml
Trying to debug this, I updated the workflow that uses the template to cat the file contents of this file:
- name: Test private action
run: |
cat ./github-actions/test/action.yml
..and I get the contents I would expect:
> Run cat ./github-actions/test/action.yml
name: Test
on: push
jobs:
test:
name: Test
runs-on: ubuntu-latest
steps:
- name: Echo
run: |
echo Heyyyyy
Why would this not be working when using it from the action repo, but the exact same content works in the target repo?

Answer 1

You have to differentiate between workflows, actions, and different action types.
Workflows are toplevel elements and not composable. Actions are building blocks that can be used in workflows. The action you defined in action.yml is actually a workflow but should be a composite run steps action, i.e. a specific type of action, that has to follow the rules given in:
https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#runs-for-composite-run-steps-actions
You can find an example for a composite run steps action here:
https://docs.github.com/en/actions/creating-actions/creating-a-composite-run-steps-action#creating-an-action-metadata-file
If you use the following as action.yaml, it should work:
name: Test
description: 'composite run action'
runs:
using: "composite"
steps:
steps:
- name: Echo
shell: bash
run: |
echo Heyyyyy