Pre-requisites

• I have double-checked my configuration
• I have tested with the :latest image tag (i.e. quay.io/argoproj/workflow-controller:latest) and can confirm the issue still exists on :latest. If not, I have explained why, in detail, in my description below.
• I have searched existing issues and could not find a match for this bug
• I'd like to contribute the fix myself (see contributing guide)

What happened? What did you expect to happen?

After upgrading from v3.7.10 to v4.0.4, using {{inputs.parameters.xxx}} in the name field of a step is no longer accepted. This worked fine in v3.7.10.

During validation (before execution), Argo replaces the parameter with an internal placeholder:

regen-{{inputs.parameters.date}}  →  regen-__argo__internal__placeholder-3305

In v3.7.10, parameters were resolved before name validation, so names like regen-05-02 were valid. In v4.0, validation now runs before parameter resolution, causing the placeholder (which contains underscores) to fail Kubernetes naming rules.

Error message:

name 'regen-__argo__internal__placeholder-3305' is invalid: name must consist of 
alpha-numeric characters or '-', and must start with an alpha-numeric character 
(e.g. My-name1-2, 123-NAME)

This also breaks when expressions that reference dynamic step names, since the step name is no longer resolved dynamically:

when: "{{steps.regen-{{inputs.parameters.date}}.status}} != Succeeded"

This is related to #14329 and PR #15744 which fixed the same placeholder leak mechanism for inline template script sources. The root cause appears to be the same (ProcessArgs substituting validation placeholders too early), but applied to a different location: the step name field instead of the script source field.

Version(s)

v4.0.4

Paste a minimal workflow that reproduces the issue. We must be able to run the workflow; don't enter a workflows that uses private images.

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: test-dynamic-step-name-
spec:
  entrypoint: main
  arguments:
    parameters:
      - name: date
        value: "2024-01-15"
  templates:
    - name: main
      steps:
        - - name: process-day
            template: day-loop
            arguments:
              parameters:
                - name: date
                  value: "{{workflow.parameters.date}}"

    - name: day-loop
      inputs:
        parameters:
          - name: date
      steps:
        - - name: run-{{inputs.parameters.date}}
            template: worker
            arguments:
              parameters:
                - name: date
                  value: "{{inputs.parameters.date}}"
            continueOn:
              failed: true
        - - name: check-{{inputs.parameters.date}}
            template: worker
            arguments:
              parameters:
                - name: date
                  value: "{{inputs.parameters.date}}"
            when: "{{steps.run-{{inputs.parameters.date}}.status}} != Succeeded"

    - name: worker
      inputs:
        parameters:
          - name: date
      container:
        image: busybox
        command: [echo]
        args: ["Processing {{inputs.parameters.date}}"]

Logs from the workflow controller

$ argo lint test-dynamic-step-name.yaml

test-dynamic-step-name.yaml:
   ✖ in "test-dynamic-step-name-" (Workflow): templates.main.steps[0].process-day 
   templates.day-loop.steps[0].name 'run-__argo__internal__placeholder-12' is invalid: 
   name must consist of alpha-numeric characters or '-', and must start with an 
   alpha-numeric character (e.g. My-name1-2, 123-NAME)

Logs from in your workflow's wait container

n/a