I would like to determine docker tag depending on building source branch.

What I’ve done so far:

variables:
  - name: isMain
    value: $[eq(variables['Build.SourceBranch'], 'refs/heads/${{ parameters.releaseBranchName }}')]
    readonly: true
  - name: isStaging
    value: $[eq(variables['Build.SourceBranch'], 'refs/heads/${{ parameters.stagingBranchName }}')]
    readonly: true
  - name: isDevelop
    value: $[eq(variables['Build.SourceBranch'], 'refs/heads/${{ parameters.buildBranchName }}')]
    readonly: true
  - name: shouldPublish
    value: $[or(variables['isMain'], variables['isStaging'], variables['isDevelop'])]
    readonly: true

  - name: tag
    ${{ if variables['isMain'] }}:
      value: $[format('release.{0}', variables['Build.BuildNumber'])]
    ${{ elseif variables['isStaging'] }}:
      value: $[format('staging.{0}', variables['Build.BuildNumber'])]
    ${{ else }}:
      value: $[format('build.{0}', variables['Build.BuildNumber'])]
    readonly: true

which evaluates like this :

  isMain:
    Parsing expression: <eq(variables['Build.SourceBranch'], 'refs/heads/main')>
    Evaluating: eq(variables['Build.SourceBranch'], 'refs/heads/main')
    Expanded: eq('refs/heads/cd', 'refs/heads/main')
    Result: 'False'
  isStaging:
    Parsing expression: <eq(variables['Build.SourceBranch'], 'refs/heads/cd')>
    Evaluating: eq(variables['Build.SourceBranch'], 'refs/heads/cd')
    Expanded: eq('refs/heads/cd', 'refs/heads/cd')
    Result: 'True'
  isDevelop:
    Parsing expression: <eq(variables['Build.SourceBranch'], 'refs/heads/develop')>
    Evaluating: eq(variables['Build.SourceBranch'], 'refs/heads/develop')
    Expanded: eq('refs/heads/cd', 'refs/heads/develop')
    Result: 'False'
  shouldPublish:
    Parsing expression: <or(variables['isMain'], variables['isStaging'], variables['isDevelop'])>
    Evaluating: or(variables['isMain'], variables['isStaging'], variables['isDevelop'])
    Expanded: or('False', variables['isStaging'], variables['isDevelop'])
    Result: 'True'
  tag:
    Parsing expression: <format('release.{0}', variables['Build.BuildNumber'])>
    Evaluating: format('release.{0}', variables['Build.BuildNumber'])
    Result: 'release.20240531.11'

I do not understand why the tag variable enters the first condition as “isMain” is set to false.

Could you please help?