Azure Pipeline条件变量未按预期工作：二级if语句失效

在Azure Pipeline YAML中配置了如下变量逻辑：

• 当Build.Reason为PullRequest时，先获取目标分支名brname，再通过表达式判断是否为main得到isPreRelease变量
• 后续基于isPreRelease的二级if语句本该执行预发布分支的变量配置，但实际未生效

原YAML片段 #

pool:
  vmImage: ubuntu-latest # Use 'windows-latest' if you have Windows native +Node modules

variables:
  ${{ if eq(variables['Build.Reason'], 'PullRequest') }}:
    brname: $[variables['System.PullRequest.targetBranchName']]
    isPreRelease: $[eq(variables['brname'], 'main')]
    ${{ if or(eq(variables['isPreRelease'], 'True'), eq(variables['isPreRelease'], True)) }}: # ---- not working
      releasename: $[ replace(variables['System.PullRequest.SourceBranch'], 'refs/heads/release/', '') ]
      format: "v{0}-rc.{1}"
      patch_version: $[counter(variables['releasename'], 1)]
    ${{ else }}:
      releasename: $[ variables['System.PullRequest.PullRequestId'] ]
      format: "PR-{0}-{1}"
      patch_version: $[counter(variables['releasename'], 1)]
    buildname: $[format(variables['format'],variables['releasename'],variables['patch_version'])]
  ${{ else }}:
    format: "development-{0}"
    buildname: $[ format(variables['format'],counter('development', 1)) ]

变量计算输出 #

Job preparation parameters
Variables:
  brname:
    Parsing expression: <variables['System.PullRequest.targetBranchName']>
    Evaluating: variables['System.PullRequest.targetBranchName']
    Result: 'main'
  isPreRelease:
    Parsing expression: <eq(variables['brname'], 'main')>
    Evaluating: eq(variables['brname'], 'main')
    Expanded: eq('main', 'main')
    Result: 'True'
  releasename:
    Parsing expression: <variables['System.PullRequest.PullRequestId']>
    Evaluating: variables['System.PullRequest.PullRequestId']
    Result: '473'
  patch_version:
    Parsing expression: <counter(variables['releasename'], 1)>
    Evaluating: counter(variables['releasename'], 1)
    Expanded: 16
    Result: '16'
  buildname:
    Parsing expression: <format(variables['format'],variables['releasename'],variables['patch_version'])>
    Evaluating: format(variables['format'], variables['releasename'], variables['patch_version'])
    Result: 'PR-473-16'

7 queue time variables used
system.pullRequest.pullRequestId : 473
system.pullRequest.sourceBranch : refs/heads/release/2.1.0
system.pullRequest.targetBranch : refs/heads/main
system.pullRequest.targetBranchName : main
system.pullRequest.sourceCommitId : 421e608d30116fc89a8b45ccccdcd39d982074a7
system.pullRequest.sourceRepositoryUri : https://CareAbout@dev.azure.com/CareAbout/DataIntegration/_git/data-factory
system.pullRequest.pullRequestIteration : 30

Azure Pipeline的两类表达式执行时机完全不同：

• ${{ }}：编译时表达式，在模板展开阶段执行，仅处理已知的编译时变量，不会计算$[ ]类型的运行时表达式结果
• $[ ]：运行时表达式，在作业准备阶段执行，编译完成后才会计算变量值

二级if使用了${{ if ... }}，此时isPreRelease的值还是未执行的运行时表达式字符串$[eq(variables['brname'], 'main')]，而非最终的True，导致判断条件永远不成立，因此走了else分支。

直接将目标分支的判断移到编译时完成——System.PullRequest.targetBranchName是编译时可用变量，无需通过运行时表达式中转。修改后的YAML配置如下：

pool:
  vmImage: ubuntu-latest # Use 'windows-latest' if you have Windows native +Node modules

variables:
  ${{ if eq(variables['Build.Reason'], 'PullRequest') }}:
    ${{ if eq(variables['System.PullRequest.targetBranchName'], 'main') }}:
      releasename: $[ replace(variables['System.PullRequest.SourceBranch'], 'refs/heads/release/', '') ]
      format: "v{0}-rc.{1}"
      patch_version: $[counter(variables['releasename'], 1)]
    ${{ else }}:
      releasename: $[ variables['System.PullRequest.PullRequestId'] ]
      format: "PR-{0}-{1}"
      patch_version: $[counter(variables['releasename'], 1)]
    buildname: $[format(variables['format'],variables['releasename'],variables['patch_version'])]
  ${{ else }}:
    format: "development-{0}"
    buildname: $[ format(variables['format'],counter('development', 1)) ]

该方案跳过了中间变量brname和isPreRelease，直接在编译时判断目标分支是否为main，避免了编译时与运行时表达式的冲突，确保分支逻辑正确触发。

内容的提问来源于stack exchange，提问作者Addy