如何在GitHub Actions的if表达式中判断requested_reviewers数组非空？

直接用以下两种可靠写法即可实现需求：

写法1：先检查字段非空再判断长度 #

if: github.event.pull_request.requested_reviewers != null && length(github.event.pull_request.requested_reviewers) > 0

写法2：结合数组存在性与非空判断 #

if: (github.event.pull_request.requested_reviewers != null) && (github.event.pull_request.requested_reviewers != [])

为什么之前的写法不生效？ #

当PR没有请求任何审阅者时，GitHub API返回的requested_reviewers字段是null，而非空数组[]。这就导致：

• 直接使用length(...) > 0会因null没有length属性而判断失效
• 直接和[]比较时，null != []的结果为true，会错误触发步骤（实际此时没有审阅者）

完整示例 #

jobs:
  trigger-on-reviewers:
    runs-on: ubuntu-latest
    steps:
      - name: Execute when reviewers are requested
        if: github.event.pull_request.requested_reviewers != null && length(github.event.pull_request.requested_reviewers) > 0
        run: |
          echo "Number of requested reviewers: ${{ length(github.event.pull_request.requested_reviewers) }}"
          echo "Reviewers: ${{ toJSON(github.event.pull_request.requested_reviewers) }}"

内容的提问来源于stack exchange，提问作者Asking