How to create a dropdown in a GitHub Actions workflow

Question

My workflow needs to receive 2 input parameters from the user. Valid values of those parameters are defined by a separate script. These values can change (not able to hard code them) so I want to populate the list dynamically when the job is to be run. The picker should update according to the result of the script allowing the user to select and only then should the actual job be run with those values as input to the job

How to provide a drop down like that?

Answer 1

Since Nov. 2021, the input type can actually be a choice list.

GitHub Actions: Input types for manual workflows

You can now specify input types for manually triggered workflows allowing you to provide a better experience to users of your workflow.
In addition to the default string type, we now support choice, boolean, and environment.

name: Mixed inputs

on:
  workflow_dispatch:
    inputs:
      name:
        type: choice
        description: Who to greet
        options: 
        - monalisa
        - cschleiden
      message:
        required: true
      use-emoji:
        type: boolean
        description: Include 🎉🤣 emojis
      environment:
        type: environment

jobs:
  greet:
    runs-on: ubuntu-latest

    steps:
    - name: Send greeting
      run: echo "${{ github.event.inputs.message }} ${{ fromJSON('["", "🥳"]')[github.event.inputs.use-emoji == 'true'] }} ${{ github.event.inputs.name }}"

That would provide a dropdown.

The question remains: can you pass a list of choices as variable to your input choice field?

You should, if you can populate the inputs context, through another job (computing your list), and calling your choice job, passing the list through jobs.<job_id>.with / jobs.<job_id>.with.<input_id>

---

Let's say I have my 'deploy' job with 'workflow_dispatch' inputs. I'll add a new 'preparation' job, which will generate a relevant choice list. But how I'll be able to call 'deploy' job manually after 'preparation' job?

Since the options are statically defined with the on.workflow_dispatch.inputs, type choice, this is not yet supported.

It was requested in this discussion:

Rather than the existing feature requests to have (filtered) tags (or branches) as choice options for a manual workflow trigger, ideally GitHub Actions would support to run a piece of code, possibly through a pre-trigger action, to populate one ore more options for the manual trigger.

One use case for pre-trigger actions could be to fill a (filtered) list of tags and/or branches.