是否仅基于树的内容计算提交的SHA-1？ [英] Is the SHA-1 of commits calculated based only on the content of the tree?

问题描述

为了进行实验，可以说您的 git log 标识了以下提交：

  commit 16bc8486fb34cf9a6faf0f7df606ae72ad9ea438 //添加第二个文件
 commit 9188f9a25b045f130b08888bc3f638099fa7f212 //初始提交
  

提交后， .git / refs / heads / master 指向16bc8486fb34cf9a6faf0f7df606ae72ad9ea438。

假设在此之后，我手动编辑 .git / refs / heads / master 文件指向9188f9a25b045f130b08888bc3f638099fa7f212

此时， git状态认识到一个新的未提交文件需要一些注意。

如果我确实提交了它，那么... git log 现在显示

 提交b317f67686f9e6ab1eaabf47073b401d677205d5 //第二次提交的第二个文件
提交9188f9a25b045f130b08888bc3f638099fa7f212 //初始提交
  

问题1：

你会注意到，在我第一次提交第二个文件并且现在， SHA 哈希值是不同的。这是为什么？文件的内容没有改变，它仍然是一样的文件。

在这一点上，原来的第二次提交发生了什么？当我做 git show 16bc8486 时，它显示了这个提交。它不会出现在 git log 历史记录中。

解决方案

问题1：由于生成的散列考虑了所有事情，包括提交元数据（本身包含日期和时间）。

问题2： git log 显示当前分支的日志。提交 16bc8486 不是它的一部分。据我所知（我不完全确定），垃圾收集器迟早会把它拿走，如果它发现它没有引用它（ git gc --help ）..

For the sake of an experiment, lets say your git log identifies the following commits

commit 16bc8486fb34cf9a6faf0f7df606ae72ad9ea438  // added 2nd file
commit 9188f9a25b045f130b08888bc3f638099fa7f212  // initial commit

After committing, .git/refs/heads/master points to 16bc8486fb34cf9a6faf0f7df606ae72ad9ea438.

Let's say, after this, i manually edit the .git/refs/heads/master file to point to 9188f9a25b045f130b08888bc3f638099fa7f212

At this point, git status recognizes that a new uncommitted file is in need of some attention. This is the same file my second commit took care of before.

If i do commit it .. git log now shows

commit b317f67686f9e6ab1eaabf47073b401d677205d5  // 2nd file committed for the 2nd time
commit 9188f9a25b045f130b08888bc3f638099fa7f212  // initial commit

Question 1:

You'll notice that SHA hashes are different between the very first time i committed a second file and now. Why is that? File's content did not change, it is still the same exact file.

Question 2

At this point, what happened to the original second commit? When i do git show 16bc8486, it shows this commit. It does not however show up in git log history.

解决方案

Question 1: Because the hash is generated taking everything into account including the commit meta data (which itself contains the date and time).

Question 2: git log shows the log of the current branch. The commit 16bc8486 is not part of it. As far as I know (I'm not completely sure) the garbage collector will take it away sooner or later, if it finds it with nothing referencing it (git gc --help)..

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