Conditional Default-Value in Azure Pipeline DevOps - azure-devops

Question

I use Azure Pipelines to Build my solution. When building manually the user can decide which Build Configuration to use. Now I want the default value (and so the value when triggered automatically) to be different according to the branch. This is my (non-working) approach:
name: PR-$(Build.SourceBranchName)-$(Date:yyyyMMdd)$(Rev:.r)
trigger:
- develop
- test
- master
pool:
vmImage: 'windows-latest'
parameters:
- name: BuildConfiguration
displayName: Build Configuration
${{ if eq(variables['Build.SourceBranch'], 'refs/heads/develop') }}:
default: Debug
${{ if eq(variables['Build.SourceBranch'], 'refs/heads/test') }}:
default: Release
${{ if eq(variables['Build.SourceBranch'], 'refs/heads/master') }}:
default: Release
values:
- Debug
- Release
The conditional part (${{...}) simply does not work. (*"A template expression is not allowed in this context")
Is there any other approach to make this happen?

Answer 1

This is not posssible to use expressins to select default value for paramataers.
Paramaters alco can't be optionla:
Parameters must contain a name and data type. Parameters cannot be optional. A default value needs to be assigned in your YAML file or when you run your pipeline. If you do not assign a default value or set default to false, the first available value will be used.
What you can do is use parameters and variables:
name: PR-$(Build.SourceBranchName)-$(Date:yyyyMMdd)$(Rev:.r)
trigger:
- develop
- test
- master
pool:
vmImage: 'windows-latest'
parameters:
- name: BuildConfiguration
displayName: Build Configuration
default: Default
values:
- Debug
- Release
- Default
variables:
- name: buildConfiguration
${{ if and(eq(variables['Build.SourceBranch'], 'refs/heads/develop'), eq(parameters.BuildConfiguration, 'Default')) }}:
value: Debug
${{ elseif and(eq(variables['Build.SourceBranch'], 'refs/heads/test'), eq(parameters.BuildConfiguration, 'Default')) }}:
value: Release
${{ elseif and(eq(variables['Build.SourceBranch'], 'refs/heads/master'), eq(parameters.BuildConfiguration, 'Default')) }}:
value: Release
${{ else }}:
value: ${{parameters.BuildConfiguration}}
steps:
- script: |
echo $(buildConfiguration)
echo $(Build.SourceBranch)