[Bug] workflow_dispatch: [] causes HTTP 500 + UI hang, not user-facing error

[cceckman]

Demonstrated in https://github.com/cceckman/actions-syntax.

name: Run tests
on:
  workflow_dispatch: []
jobs:
  build-and-test:
    runs-on: ubuntu-latest
    steps:
    - uses: 'actions/checkout@v3'
    - run: 'echo Done'

This seems to parse fine within the UI; the Actions page has the relevant blue bar for triggering workflow_dispatch.

Clicking on "Run workflow" just gives a spinner:

The network trace for developer tools shows an HTTP 500 response for the URL https://github.com/cceckman/actions-syntax/actions/manual?workflow=.github%2Fworkflows%2Fbuggy.yml after that click.

---

IIUC, the underlying code has an error - workflow_dispatch is supposed to be an object ({}), not a list ([]).

But: I'd expect that to come out as a user-visible error, "The syntax for this dispatch is incorrect", rather than a hang and a 500.

[cceckman]

FWIW, this also shows up from the CLI:

∵ gh workflow run buggy.yml                                       
could not create workflow dispatch event: HTTP 500 (https://api.github.com/repos/cceckman/actions-syntax/actions/workflows/24345361/dispatches)

And I can confirm (from another repository) that changing to workflow_dispatch: {} fixes the issue.

[mygizli04]

I made the exact same error and got the exact same issue, surprised it didn't give any errors!

[RozbehSharahi]

Wow thx that just saved me hours of frustration :D