Differentiate between input parameter empty or not present

[rsenden]

Current behavior:

• If an input parameter is defined in action.yml (without default value), GitHub will set the INPUT_PARAMNAME environment variable to an empty value if the parameter is not present in the workflow

Expected behavior:

• If an input parameter is defined in action.yml (without default value), GitHub should not set the INPUT_PARAMNAME environment variable to an empty value if the parameter is not present in the workflow

Possibly related issue for JavaScript actions: actions/toolkit#272

Resources that illustrate this issue:

• Dockerfile: https://github.com/rsenden/test-empty-var-action/blob/master/Dockerfile
• GitHub Action for this Docker image: https://github.com/rsenden/test-empty-var-action/blob/master/action.yml
• Sample workflow that invokes this Docker image both directly and through the action, with the test input parameter not set: https://github.com/rsenden/test-empty-var-action/blob/master/.github/workflows/notset.yml
• Workflow output: https://github.com/rsenden/test-empty-var-action/runs/1707506513?check_suite_focus=true

As can be seen in the workflow output, results are different between running the Docker image directly or through the GitHub Action.

This can cause issues if a Docker image (or other action implementation) differentiates between 'empty' and 'not set'. If an action wants to set an empty value as the default value, then this should be done using the default property in the action definition.

Can you please get this fixed?

[hross]

This is currently a low priority for us in terms of where it falls in our bug priority. I am marking it a papercut but I don't expect us to be able to get to fixing it soon.

[lucacome]

I just stumbled on this, any way those PRs are going to be merged anytime soon?

[shrink]

@hross if anything is needed from my end to move the merge of my fixes forward, please let me know, happy to do any additional work required to get this fixed :-)

[rethab]

Hi @hross I'd like to bring this to your attention again. This problem is made worse in combination with reusable workflows:

Specifically, while the author of an action cannot distinguish between "no input passed" and "empty string passed", the runner does seem to distinguish between the two when deciding whether to use defaults: If an empty string is passed as an input, then the default value is not used, but when the input is omitted entirely, then the default is used.

Now consider reusable workflows. Imagine a main workflow that calls a reusable workflow which in turn calls an action. There is one input, which is passed all the way down to the action. If the main workflow doesn't specify the input to the reusable workflow, then the runner still turns that into an empty string. That empty string is then passed on to the action, where the default value is not used.

So it is the runner that turns "no input passed" into "empty string passed" and then it reaches the action where the default is not used. This makes it tricky to handle default values with reusable workflows.

Also cc @chrispat

Example

Action

name: Test
description: Test Action

inputs:
  greeting:
    required: false
    description: 'Greeting to use.'
    default: 'Hello'

runs:
  using: 'composite'
  steps:
    - run: echo ${{ inputs.greeting }} Earthling
      shell: bash

Partial Workflow

on:
  workflow_call:
    inputs:
      greeting:
        description: "The greeting to use"
        required: false
        type: string

jobs:
  greet:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: ./
        with:
          greeting: ${{ inputs.greeting }}

Main Workflow

jobs:
  greet:
    uses: rethab/actions-test-repo/.github/workflows/partial.yml@main

Output

[sean-m-sullivan]

Hello @hross I've been looking into an issue with a Github marketplace action, and found that this also is an issue there. It is nearly if not completely impossible to evaluate an input argument as null without these changes going through. I highly support this PR to go through.