GitHub Actions中无法获取subtask/bugfix分支父分支的问题

我配置了一个GitHub Actions工作流，当代码推送到subtask/*或bugfix/*前缀的分支时自动创建PR。这些分支都是从story/*、task/*或production分支拉取创建的。本地执行git命令能正常获取父分支名称，但在GitHub Actions中执行时，PARENT_BRANCH输出为空。

本地可正常运行的命令 #

# 获取当前分支名称
CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)

# 确定父分支
PARENT_BRANCH=$(git show-branch | sed "s/].*//" | grep "*" | grep -v "${CURRENT_BRANCH}" | head -n1 | sed "s/^.*\[//")

GitHub Actions工作流配置 #

name: Auto-create PR when changes pushed to subtask/* or bugfix/*

# 当代码推送到subtask/*或bugfix/*分支时，自动创建PR将其合并到父分支
on:
  push:
    branches:
      - subtask/*
      - bugfix/*

jobs:
  createPR:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v3
        with:
          repository: {my-repo-name}
          token: ${{ secrets.GIT_ACCESS_TOKEN }}

      - name: Determine parent branch
        id: determine-parent-branch
        run: |
          # 获取当前分支名称
          CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)

          # 确定父分支
          PARENT_BRANCH=$(git show-branch | sed "s/].*//" | grep "*" | grep -v "${CURRENT_BRANCH}" | head -n1 | sed "s/^.*\[//")

          echo "PARENT_BRANCH=${PARENT_BRANCH}"

      - name: Create pull request from ${{ github.ref_name }} to ${{ steps.determine-parent-branch.outputs.PARENT_BRANCH }}
        uses: repo-sync/pull-request@v2
        with:
          github_token: ${{ secrets.GIT_ACCESS_TOKEN }}
          pr_label: "automerge"
          pr_title: "Auto-PR from ${{ github.ref_name }} to ${{ steps.determine-parent-branch.outputs.PARENT_BRANCH }}"
          destination_branch: ${{ steps.determine-parent-branch.outputs.PARENT_BRANCH }}

问题原因 #

actions/checkout@v3默认只克隆当前推送的分支，且仅拉取最新的一次提交（浅克隆），本地仓库中没有其他分支的引用信息。而git show-branch需要本地存在父分支的引用才能解析出对应的分支名称，所以在GitHub Actions环境中执行时会返回空值。另外，原步骤中echo "PARENT_BRANCH=${PARENT_BRANCH}"的写法无法将变量设置为步骤输出，后续步骤也无法读取到该值。

解决方案 #

方案1：调整checkout参数并拉取全部分支 #

修改checkout步骤，拉取完整仓库历史并同步所有远程分支：

- name: Checkout repository
  uses: actions/checkout@v3
  with:
    repository: {my-repo-name}
    token: ${{ secrets.GIT_ACCESS_TOKEN }}
    fetch-depth: 0  # 拉取完整仓库历史
    ref: ${{ github.ref }}

- name: Fetch all remote branches
  run: git fetch origin '+refs/heads/*:refs/remotes/origin/*'

同时修正步骤输出的写法：

- name: Determine parent branch
  id: determine-parent-branch
  run: |
    CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
    PARENT_BRANCH=$(git show-branch | sed "s/].*//" | grep "*" | grep -v "${CURRENT_BRANCH}" | head -n1 | sed "s/^.*\[//")
    echo "PARENT_BRANCH=${PARENT_BRANCH}" >> "$GITHUB_OUTPUT"

方案2：改用更可靠的父分支检测逻辑 #

不需要依赖本地分支引用，直接通过远程分支判断当前分支的派生来源：

- name: Determine parent branch
  id: determine-parent-branch
  run: |
    CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
    # 定义可能的父分支候选列表
    PARENT_CANDIDATES=("production" "task/*" "story/*")
    
    for candidate in "${PARENT_CANDIDATES[@]}"; do
      # 匹配远程分支
      REMOTE_BRANCHES=$(git ls-remote --heads origin "$candidate")
      if [[ -n "$REMOTE_BRANCHES" ]]; then
        for branch in $(echo "$REMOTE_BRANCHES" | awk '{print $2}' | sed 's/refs\/heads\///'); do
          # 检查当前分支是否从该分支派生
          if git merge-base --is-ancestor origin/"$branch" HEAD; then
            PARENT_BRANCH="$branch"
            break 2  # 找到后退出循环
          fi
        done
      fi
    done
    
    echo "PARENT_BRANCH=${PARENT_BRANCH}" >> "$GITHUB_OUTPUT"

内容的提问来源于stack exchange，提问作者Keith Yeoh