document some of the pitfalls of using private or internal reusable workflows in a public repo

[jsoref]

Code of Conduct

• I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#jobsjob_iduses

What part(s) of the article would you like to see updated?

Add a warning

Warning

If you use uses: my-org/other-repo/.github/actions/shared-action@main then anyone who would trigger the workflow (as determined by on: ... conditions) especially in forks, but quite likely not limited to forks and doesn't have access to your my-org/other-repo repository will encounter an unfixable error of this form:

Invalid workflow file: .github/workflows/moda-ci.yaml#L86
error parsing called workflow ".github/workflows/moda-ci.yaml" -> "github/internal-actions/.github/workflows/docker_security.yml@main" : workflow was not found. See https://docs.github.com/actions/learn-github-actions/reusing-workflows#access-to-reusable-workflows for more information.

It's possible to avoid this by using a combination of a workflow_call with a jobs: / if: condition that guards against the user from tripping on the problem e.g. ${{ github.repository == 'github/docs-internal' }} and then have the on: workflow_call on the internal side be responsible for using the reusable workflow.

Additional information

• Misleading section "Example: Using an action inside a different private repository than the workflow" in "Workflow Syntax" #34562 (comment)
• Misleading section "Example: Using an action inside a different private repository than the workflow" in "Workflow Syntax" #34562 (comment)
• moda-ci.yaml triggers an error in forks for anyone who doesn't have access to github/docs-internal #35731

[nguyenalex836]

@jsoref Thank you for raising this issue! I'll get this triaged for review ✨ Our team will provide feedback regarding the best next steps for this issue - thanks for your patience! 💛