Lifecycle Hooks arguments and support for Steps / DAGs

[mshatkhin23]

Pre-bug-report checklist

1. This bug can be reproduced using YAML

• Yes 👉 Please report a bug to the Argo Workflows GitHub 👈
• No

2. This bug occurs when...

• running Hera code without submitting to Argo (e.g. when exporting to YAML)
• running Hera code and submitting to Argo

Bug report

Describe the bug
So this issue describes 2 different "issues" - 1 is more of a shortcoming in Argo, the other seems to be a Hera bug:

1. hooks do not seem to work on Steps / DAGs; I cant seem to find any examples applying hooks to Steps / DAGs in the upstream tests on hooks so I believe this is an upstream shortcoming. This issue comment motivated a workaround by applying the hook on the step of a Steps wrapper, but I guess thats sub-optimal. Is there any reason hooks shouldn't be allowed on Steps / DAGs?
2. The second issue does seem to be a bug in Hera -- and has to do with building the arguments for a hook. When I try to supply arguments to the hook for a WT or Step / Task, it seems to build an empty arguments object.

To Reproduce
Full Hera code to reproduce the bug:

@script(constructor="inline")
def echo(message: Annotated[str, Parameter(description="A message to print")]) -> None:
    """Prints out a message."""
    print(message)

with WorkflowTemplate(
        name="mlplatform.test-hooks",
        entrypoint="wrapper-steps",
        hooks={
            "wt-exit": m.LifecycleHook(
                template="echo",
                arguments={"message": "on exit"},
            )
        },
    ) as wt:
        with DAG(name="main-dag", inputs=[Parameter(name="a")]) as main_dag:
            task1 = echo(
                name="echo1",
                arguments={"message": "hello main: {{inputs.parameters.a}}"},
            )
            task2 = echo(name="echo2", arguments={"message": "hello main 2"})
            task1 >> task2

        with Steps(name="wrapper-steps"):
            main_dag(
                hooks={
                    "dag-exit": m.LifecycleHook(
                        template="echo", arguments={"message": "on exit"}
                    )
                },
                arguments={"a": "WORLD"},
            )
            echo(
                name="echo3",
                arguments={"message": "hello world 3"},
                hooks={
                    "echo-exit": m.LifecycleHook(
                        template="echo", arguments={"message": "on exit"}
                    )
                },
            )
        return wt

Generates to:

apiVersion: argoproj.io/v1alpha1
kind: WorkflowTemplate
metadata:
  name: mlplatform.test-hooks-v0.0.1-alpha
spec:
  entrypoint: wrapper-steps
  hooks:
    wt-exit:
      arguments: {}
      template: echo
  templates:
  - dag:
      tasks:
      - arguments:
          parameters:
          - name: message
            value: 'hello main: {{inputs.parameters.a}}'
        name: echo1
        template: echo
      - arguments:
          parameters:
          - name: message
            value: hello main 2
        depends: echo1
        name: echo2
        template: echo
    inputs:
      parameters:
      - name: a
    name: main-dag
  - inputs:
      parameters:
      - description: A message to print
        name: message
    name: echo
    script:
      ... (removing for brevity) ...
  - name: wrapper-steps
    steps:
    - - arguments:
          parameters:
          - name: a
            value: WORLD
        hooks:
          dag-exit:
            arguments: {}
            template: echo
        name: main-dag
        template: main-dag
    - - arguments:
          parameters:
          - name: message
            value: hello world 3
        hooks:
          echo-exit:
            arguments: {}
            template: echo
        name: echo3
        template: echo

Expected behavior

• The Steps / DAGs issue seems to be an upstream shortcoming / issue so it could be nice to just add an example documenting the work-around.
• The hook arguments should be correctly built when generating the yaml

Environment

• Hera Version: 5.9.0
• Python Version: 3.9.18

[elliotgunton]

For Hera's lifecycle hooks, they currently require a full model LifecycleHook object, as there is no special Hera class for these yet. See example here. I can take a look into the steps/dags exit hooks, but will be an issue upstream if needed, and will close this one.