AzureDevOps yaml template - expression as parameter default value

Question

I want to have an expression as a default value for a parameter but I get "a template expression is not allowed in this context" Since templates cannot have variables unless they ONLY have variables (another thing I don't get...), I am looking for other alternatives. Anyone has any idea?

What I'm trying is this:

parameters:
  - name: paramOne
    default: ${{ lower(replace('$(System.TeamProject)',' ','')) }}
    type: string

EDIT

Here's a full example. This is azure-pipelines.yml

trigger:
- main

pool:
  vmImage: windows-2019

steps:
- template: test-template.yml

This is test-template.yml:

parameters:
  - name: paramOne
    default: ${{ lower(replace(variables['System.TeamProject'],' ','')) }}
    type: string
steps:
- task: PowerShell@2
  displayName: "Run PowerShell script"
  inputs:
    targetType: 'inline'
    script: Write-Host "${{parameters.paramOne}}"

This results in the error: "a template expression is not allowed in this context"

Variables cannot be added to test-template.yml, as indicated here: https://learn.microsoft.com/en-us/azure/devops/pipelines/process/templates?view=azure-devops#variable-reuse "If you are using a template to include variables in a pipeline, the included template can only be used to define variables"

Answer 1

Ok, then I would propose the following workaround

parameters:
  - name: paramOne
    displayName: 'My param. Leave empty to populate with default value (project name). bla bla...'
    default: ''
    type: string

steps:

- task: PowerShell@2
  name: 'setVar'
  inputs:
    targetType: inline
    script: |
      if( "${{ parameters.paramOne }}" -eq "") {
        $val = "$(System.TeamProject)".ToLower().Replace(" ","")
      } else {
        $val = "${{ parameters.paramOne }}"
      }
      echo "##vso[task.setvariable variable=varOne]$val"

and from there on use varOne instead of paramOne

Answer 2

It looks that this is not possible. I tested with this:

parameters:
  - name: paramOne
    default: $[lower(replace(variables['System.TeamProject'],' ',''))]
    type: string
  - name: paramTwo
    default: $(runtimeVar)
    type: string
  - name: paramThree
    default: $(compileVar)
    type: string
steps:
- task: PowerShell@2
  displayName: "Run PowerShell script"
  inputs:
    targetType: 'inline'
    script: |
      Write-Host "${{parameters.paramOne}}"
      Write-Host "${{parameters.paramTwo}}"
      Write-Host "${{parameters.paramThree}}"

and

trigger: none

variables:
  runtimeVar: $[lower(replace(variables['System.TeamProject'],' ',''))]
  compileVar: ${{ lower(replace(variables['System.TeamProject'],' ','')) }}

pool:
  vmImage: windows-2019

steps:
- template: parameter-with-default-runtime-template.yml

and I got:

$[lower(replace(variables['System.TeamProject'],' ',''))]
devopsmanual
devopsmanual

So you see, the same syntax which is used to populate variable doesn't do the same when you use it as default for parameter.