在 Windows 上签出 HEAD（和变体）时出现奇怪的 Git 行为

Question

设置

让我们想象一个简单的存储库，如下所示。可以看到HEAD指向master

$ git log --decorate --graph
* commit 99d20608088ba9c74b57e36a1b0b79ff2be42d68 (HEAD, master)
| Author: Saaman <user@domain.com>
| Date:   Wed Apr 17 16:53:50 2013 +0200
|
|     My third commit
|
* commit a4a040c8b5c3923a2ba0f652caae0540f84c4c98
| Author: Saaman <user@domain.com>
| Date:   Wed Apr 17 16:53:27 2013 +0200
|
|     My second commit
|
* commit c5d20f203c11acbb9238ab77581e27a15ccde25e
  Author: Saaman <user@domain.com>
  Date:   Wed Apr 17 16:52:58 2013 +0200

      My first commit

$ git reflog
99d2060 HEAD@{0}: commit: My third commit
a4a040c HEAD@{1}: commit: My second commit
c5d20f2 HEAD@{2}: commit (initial): My first commit

行动

现在，让我们执行一些结帐操作

$ git checkout master
Already on 'master'

$ git reflog
99d2060 HEAD@{0}: checkout: moving from master to master
99d2060 HEAD@{1}: commit: My third commit
a4a040c HEAD@{2}: commit: My second commit
c5d20f2 HEAD@{3}: commit (initial): My first commit

$ git checkout HEAD

$ git reflog
99d2060 HEAD@{0}: checkout: moving from master to master
99d2060 HEAD@{1}: commit: My third commit
a4a040c HEAD@{2}: commit: My second commit
c5d20f2 HEAD@{3}: commit (initial): My first commit

reflog 显示

• 签出 HEAD 不会在 reflog 中产生任何条目
• 签出master会在reflog中插入一个新条目（说明HEAD从master移动到master）

让我们试试别的方法

$ git checkout head
Note: checking out 'head'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b new_branch_name

HEAD is now at 99d2060... My third commit

$ git reflog
99d2060 HEAD@{0}: checkout: moving from master to head
99d2060 HEAD@{1}: checkout: moving from master to master
99d2060 HEAD@{2}: commit: My third commit
a4a040c HEAD@{3}: commit: My second commit
c5d20f2 HEAD@{4}: commit (initial): My first commit

现在显示 reflog

• head 已解析为相同的 SHA 99d2060
• HEAD 现已分离
• 一个新条目已插入到 reflog（说明 HEAD 从 master 移动到 head）

问题

我很难理解这些行为。

• 为什么签出HEAD 不会在reflog 中产生任何内容，而签出master（指向HEAD 的分支）却会？
• 为什么签出head（小写）会分离HEAD，而git 可以成功地将其剥离到同一个提交？

注意：这些测试是在 Windows/msysgit 上进行的

Answer 1

分析代码后，给出一些答案：

• 无论 HEAD 是否分离，git checkout HEAD 都不会记录任何内容。
• 从“master”移动到“master”并不是真正有用的信息，因为分支及其目标都没有改变。填写日志的一些无用信息，但非常无害。
• git checkout head 在 Linux 上不起作用。它仅适用于 Windows，因为文件系统不区分大小写。