How to refer a variable in parameters block in azure pipelines

Question

I'd like to set default value of a parameter from a variable. Unfortunately, below pipeline throws this error The 'Environment' parameter value '$[variables.deployToEnv]' is not a valid value.

I tried it with other expressions too but it doesn't work. How can I solve this problem?

variables:
  - name: deployToEnv
    ${{ if in(variables['Build.SourceBranchName'], 'Development') }}:
      value: dev
    ${{ if in(variables['Build.SourceBranchName'], 'Staging', 'Testing') }}:
      value: test
    ${{ if in(variables['Build.SourceBranchName'], 'Production') }}:
      value: prod

parameters:
  - name: Environment
    type: string
    displayName: Environment
    default: $(deployToEnv)
    # default: $[variables.deployToEnv]
    # default: ${{ variables.deployToEnv }}
    values:
      - dev
      - test
      - prod

Answer 1

From my experience, it was simply impossible to reference a variable in parameters context.

I found solution for my problem by flipping dependency. Instead setting parameter base on a variable, I set a variable base on a parameter.

parameters:
  - name: Environment
    type: string
    displayName: Environment
    default: none
    values:
      - none
      - dev
      - test
      - prod

variables:
  - name: deployToEnv
    ${{ if not(eq(parameters.Environment, 'none')) }}:
      value: ${{ parameters.Environment }}
    ${{ if and(eq(parameters.Environment, 'none'), in(variables['Build.SourceBranchName'], 'Development')) }}:
      value: dev
    ${{ if and(eq(parameters.Environment, 'none'), in(variables['Build.SourceBranchName'], 'Staging', 'Testing')) }}:
      value: test
    ${{ if and(eq(parameters.Environment, 'none'), in(variables['Build.SourceBranchName'], 'Production')) }}:
      value: prod
  - group: k8s-cluster-${{ variables.deployToEnv }}

Answer 2

This is because parameters are parsed early in the processing of the pipeline before the variables are computed. So you cannot set a parameter based on a variable.

This is not really a problem you just have to re-think the flow of your pipeline.

You have not provided details how you are trying to use this parameter so it's difficult to help solve your problem.

@Lukasz suggestion of using conditional insertions is useful.