Variable interpolation doesn't work in stepTemplate

[vdemeester]

Expected Behavior

Given the following TaskRun (using embedded Task, but it's the same with Task references), it fails with InvalidImageName, as the image name passed to kubernetes is $(params.image)(aka not interpolated).

apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  generateName: steptemplate-variables-
spec:
  params:
  - name: image
    value: ubuntu
  taskSpec:
    params:
    - name: image
    stepTemplate:
      image: $(params.image)
    steps:
    - name: foo
      script: |
        echo hello from $(params.image)

Actual Behavior

It resolves the param value and "just" work.

Steps to Reproduce the Problem

1. Create a TaskRun similar to above
2. Apply it
3. See it fail

Additional Info

• Kubernetes version:

  Output of kubectl version:

Server Version: version.Info{Major:"1", Minor:"21", GitVersion:"v1.21.1", GitCommit:"5e58841cce77d4bc13713ad2b91fa0d961e69192", GitTreeState:"clean", BuildDate:"2021-05-21T23:01:33Z", GoVersion:"go1.16.4", Compiler:"gc", Platform:"linux/amd64"}

• Tekton Pipeline version:

  Output of tkn version or kubectl get pods -n tekton-pipelines -l app=tekton-pipelines-controller -o=jsonpath='{.items[0].metadata.labels.version}'

Pipeline version: v0.35.0

[vdemeester]

/assign