Interpolating local var source in vars property of a task step

[multimac]

With the new local var source, is there any way to pass local vars into a task defined in a file?

My attempts to do so end up with the uninterpolated value being sent to the task, ie. ((.:image)) instead of the value of image from the local var source.

eg.
Pipeline

- name: do-something-with-image-digest
  serial: true
  plan:
  - get: image-name
  - load_var: image
    file: image-name/digest
  - task: write-image-digest-somewhere
    file: task.yml
    vars:
      image: ((.:image))

Task

...

run:
  path: echo
  args:
  - "The image is:"
  - ((image))

Expected
The image is: sha256:780cdc...

Actual
The image is: ((.:image))

[jamieklassen]

The docs on dynamic vars for a task mention that

The following attributes can be parameterized through a var source:
...

• task step params on a task step in a pipeline
• Tasks in their entirety - whether from task step file or task step config in a pipeline...

so I think the problem you're encountering is that, when you have a task step, variable interpolation only happens on the params and config fields, or the whole config read from the file. In particular, no interpolation is done on the vars field. Now, there may be a valid use case here for "var mapping" in a manner similar to, say, input_mapping, but we don't have that feature yet and I haven't thought through whether it's really desirable.

That said, I see two paths for you to get unblocked:

1. Use params interpolation. This means your pipeline should look like

   @@ -6,5 +6,5 @@
        file: image-name/digest
      - task: write-image-digest-somewhere
        file: task.yml
   -    vars:
   +    params:
          image: ((.:image))

   and your task should look something like

   @@ -1,8 +1,11 @@
    ...
   
   +params:
   +  image:
    run:
   -  path: echo
   +  path: sh
      args:
   -  - "The image is:"
   -  - ((image))
   +  - -c
   +  - |
   +    echo "The image is: $image"

2. Use the . var source directly in the task. So you could drop the vars from the task step in your pipeline, and your task config would become

   @@ -4,5 +4,5 @@
      path: echo
      args:
      - "The image is:"
   -  - ((image))
   +  - ((.:image))

[vito]

Hmm, this should probably be fixed. I would have expected that syntax to work. I'll open an issue.

edit: opened #5609