Substitute params by index

[popcor255]

Feature request

Currently prams can be substituted by key (string substitute). However, params is an array of type param. I would like to reference a parameter by the index in the params array rather than the key.

TLDR; Array of Type Params is not the same as Param that is Type Array. We should probably fix this.

(how array access would look)
Request:

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: simple-task
spec:
  params:
    - name: param
      type: string
  steps:
  - name: alpine
    image: alpine
    command: [ "echo" ]
    args: [ "$(params[0])" ]

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: simple-task
spec:
  params:
    - name: param
      type: array
  steps:
  - name: alpine
    image: alpine
    command: [ "echo" ]
    args: [ "$(params[0][*])" ]

The above tasks should produce the same result as these tasks:

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: simple-task
spec:
  params:
    - name: param
      type: string
  steps:
  - name: alpine
    image: alpine
    command: [ "echo" ]
    args: [ "$(params.param)" ]

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: simple-task
spec:
  params:
    - name: param
      type: array
  steps:
  - name: alpine
    image: alpine
    command: [ "echo" ]
    args: [ "$(params.param[*])" ]

These two tasks should produce the same result.
Note : This implementation requires indexes to be declared before runtime.

[bobcatfish]

Related issue: #1393 <-- in that issue I believe @skaegi is suggesting a broader syntax for accessing param values (i think jsonpath based?)

I think we could totally tackle the features one at a time if that's easiest, as long as they are all headed in the same direction - and afaik the syntax above is how array access would look?

might be worth bringing up in the API wg too: https://github.com/tektoncd/community/blob/master/working-groups.md#api

[popcor255]

I added the example with array types. It is just using bracket annotation instead of dot annotation. However, with bracket annotation we can use the type to distinguish index(int)/key(string).

[popcor255]

Quick and Dirty POC: https://github.com/popcor255/pipeline/tree/replace-by-index-without-validation
It was like 2 line code change o _o

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: simple-task
spec:
  params:
    - name: param
      type: string
  steps:
  - name: alpine
    image: alpine
    command: [ "echo" ]
    args: [ "$(params.0)" ]

[popcor255]

The main issue I am trying to highlight is that an Array of Type Params is not the same as Param that is Type Array. I think there should be a discussion on if there should be some effort on keeping them the same or at the very least have a clear distinction.

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: sleepy-with-nested-params
spec:
  params:
    - name: myParams
      type: array
  steps:
  - name: alpine
    image: alpine
    command: [ "echo" ]
    args: [ "$(params.myParams[*])" ]
---
apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  generateName: run-with-sleepy-with-nested-params
spec:
  taskRef:
    name: sleepy-with-nested-params
  params:
    - name: myParams
      value:
        - "test=testing"
        - "env=test"

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: sleepy-with-psuedo-params
spec:
  params:
    - name: test
    - name: env
  steps:
  - name: alpine
    image: alpine
    command: [ "echo" ]
    args: [ "$(params[*])" ]
---
apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  generateName: run-with-sleepy-with-psuedo-params
spec:
  taskRef:
    name: sleepy-with-psuedo-params
  params:
    - name: test
      value: testing
    - name: env
      value: testing

[popcor255]

#1020
/close