git subtree有效管理公共第三方lib

　　如果你的项目中有很多第三方的lib，你希望使用它，并且也希望可能对该lib做修改并且贡献到原始的项目中去，或者你的项目希望模块化，分为几个repo单独维护，那么git subtree就是一个选择。

　　git subtree是附属于git的附加工具，默认情况下并不会安装。https://github.com/git/git/tree/master/contrib/subtree。

# git clone https://github.com/git# cd git

# make prefix=/usr/local/git install

# echo "export PATH=$PATH:/usr/local/git/bin" >> /etc/bashrc
# source /etc/bashrc# cd contrib/subtree# make prefix=/usr/local/git/bin

# make prefix=/usr/local/git/bin install

# make prefix=/usr/local/git/bin install-doc

# cp git-subtree /usr/local/git/bin

就ok了！

　　在本文中，我们假设我们工作在subtree-p这个项目中（放在github上的一个repo），而在该项目中，我们需要subtree-sub这个子模块（或者说是Lib）.

　　当前我们的subtree-p项目中，没有引入任何subtree-sub这个模块，现在我们通过以下命令来实现：

(master)$ git remote add subtree-sub-remote https://github.com/cnweibo/subtree-sub.git
(master)$ git remote -v
origin  https://github.com/cnweibo/subtree-p.git (fetch)
origin  https://github.com/cnweibo/subtree-p.git (push)
subtree-sub-remote      https://github.com/cnweibo/subtree-sub.git (fetch)
subtree-sub-remote      https://github.com/cnweibo/subtree-sub.git (push)
(master)$ pwd
/home/cabox/workspace/subtreetest/subtree-p
(master)$ ls
README.md
(master)$ git subtree add --prefix=mysubtree subtree-sub-remote master
git fetch subtree-sub-remote master
warning: no common commits
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 0
Unpacking objects: 100% (3/3), done.
From https://github.com/cnweibo/subtree-sub
 * branch            master     -> FETCH_HEAD
 * [new branch]      master     -> subtree-sub-remote/master
Added dir ‘mysubtree‘
(master)$ ls
README.md  mysubtree
(master)$ ls -la mysubtree/
total 12
drwxrwxr-x 2 cabox cabox 4096 May 31 02:14 .
drwxrwxr-x 4 cabox cabox 4096 May 31 02:14 ..
-rw-rw-r-- 1 cabox cabox   14 May 31 02:14 README.md     

上面的一系列命令中，首先在subtree-p项目目录中引入了subtree-sub这个子项目，它存放在目录mysubtree中，和我们的subtree-sub-remote这个remote相对应。这时，subtree-p项目由于增加了新的目录（subtree-sub子项目repo），因此需要commit和push.

注意：在mysubtree这个子目录中是没有任何.git文件的，它实际上是subtree-sub这个子项目repo的纯代码copy！！

(master)$ git s
On branch master
Your branch is ahead of ‘origin/master‘ by 2 commits.
  (use "git push" to publish your local commits)
nothing to commit, working directory clean
(master)$ git push
Username for ‘https://github.com‘: kidsit
Password for ‘https://[email protected]‘:
Counting objects: 5, done.
Delta compression using up to 12 threads.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (5/5), 528 bytes | 0 bytes/s, done.
Total 5 (delta 0), reused 0 (delta 0)
To https://github.com/cnweibo/subtree-p.git
   67da25d..c1e6018  master -> master       

这时，我们查看在github上的subtree-p repo，你就可以看到这个父项目已经引入了mysubtree（代表了subtree-sub repo！）

现在我们在parent项目中对子项目做修改并且commit, push：

(master)$ echo "kidsit add subfile1 within parent" >subfile1
(master)*$ git s
On branch master
Your branch is up-to-date with ‘origin/master‘.
Untracked files:
  (use "git add <file>..." to include in what will be committed)                                                                                                           

        subfile1                                                                                                                                                           

nothing added to commit but untracked files present (use "git add" to track)
(master)*$ git a .
(master)*$ git ci "kidsit add subfile1 within parent"
[master ed30a68] kidsit add subfile1 within parent
 1 file changed, 1 insertion(+)
 create mode 100644 mysubtree/subfile1
(master)$ git s
On branch master
Your branch is ahead of ‘origin/master‘ by 1 commit.
  (use "git push" to publish your local commits)
nothing to commit, working directory clean
(master)$ git push
Username for ‘https://github.com‘: kidsit
Password for ‘https://[email protected]‘:
Counting objects: 4, done.
Delta compression using up to 12 threads.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (4/4), 398 bytes | 0 bytes/s, done.
Total 4 (delta 0), reused 0 (delta 0)
To https://github.com/cnweibo/subtree-p.git
   c1e6018..ed30a68  master -> master
(master)$                      

这时我们再查看github上的subtree-p我们就能看到我们对子项目的新的改动了：

我们来继续模拟代码开发过程：修改subtree-p和subtree-sub后，统一一次性做一个提交：

(master)$ echo "kidsit change README for p" >README.md
(master)*$ echo "kidsit add new subfileNew2 " >mysubtree/subfileNew2
(master)*$ git s
On branch master
Your branch is up-to-date with ‘origin/master‘.
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)                                                                                                

        modified:   README.md                                                                                                                                              

Untracked files:
  (use "git add <file>..." to include in what will be committed)                                                                                                           

        mysubtree/subfileNew2                                                                                                                                              

no changes added to commit (use "git add" and/or "git commit -a")
(master)*$ git a .
(master)*$ git ci "kidsit change p and s in ONE commit"
[master a27d335] kidsit change p and s in ONE commit
 2 files changed, 2 insertions(+), 2 deletions(-)
 create mode 100644 mysubtree/subfileNew2
(master)$ git push
Username for ‘https://github.com‘: kidsit
Password for ‘https://[email protected]‘:
Counting objects: 5, done.
Delta compression using up to 12 threads.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (5/5), 461 bytes | 0 bytes/s, done.
Total 5 (delta 0), reused 0 (delta 0)
To https://github.com/cnweibo/subtree-p.git
   ed30a68..a27d335  master -> master
(master)$                               

这时，我们要注意，我们再subtree-p项目中对父项目和子项目分别都做了修改，但是子项目本身的repo还没有做过任何更新，它根本不知道你曾经做过修改，这时，如果你希望将你对子项目的修改贡献出来，可以执行git subtree push命令

(master)$ git push
Username for ‘https://github.com‘: kidsit
Password for ‘https://[email protected]‘:
Counting objects: 5, done.
Delta compression using up to 12 threads.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (5/5), 461 bytes | 0 bytes/s, done.
Total 5 (delta 0), reused 0 (delta 0)
To https://github.com/cnweibo/subtree-p.git
   ed30a68..a27d335  master -> master
(master)$ git subtree push --prefix=mysubtree/ subtree-sub-remote master
git push using:  subtree-sub-remote master
Username for ‘https://github.com‘: kidsit
Password for ‘https://[email protected]‘:
Counting objects: 6, done.
Delta compression using up to 12 threads.
Compressing objects: 100% (4/4), done.
Writing objects: 100% (6/6), 563 bytes | 0 bytes/s, done.
Total 6 (delta 1), reused 0 (delta 0)
To https://github.com/cnweibo/subtree-sub.git
   9a0ef93..001c5d8  001c5d86c4da43ab676aaeb49763d5353353159f -> master                                                                                                    

上面我们分别对subtree-p这个父项目和subtree-sub这个子项目分别作了push操作分享（一般来说对子项目push是非常少见的动作，因为我们更多的是拿别人的lib来用而不是开发），这时如果我们去看github上的两个项目repo的commit历史，你会发现两个repo上都有了同一个commit！！

正因为如此，我们最好是将父项目和子项目分别做commit，不要混淆在一起！这样做的好处是git subtree push时，git会自动将对父项目和子项目的commit区分清楚的，对父项目的修改不会出现在子项目repo修改历史中！