【Git 学习笔记】第三章分支、合并及配置项（上）

2024-07-11 16:16:03
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第三章分支、合并及配置项

3.1 本地分支管理

假如 git 库就在本地，即便无需远程共享代码，本地分支也可以像需要远程共享的仓库那样进行管理。正如本例所示，需要先复制一个仓库到本地，意味着存在一个远程库。

# clone the jgit repository to match
$ git clone https://git.eclipse.org/r/jgit/jgit 
$ cd jgit 
# Whenever you start working on a bug fix or a new 
# feature in your project, you should create a branch
$ git branch newBugFix 
$ git branch 
* master 
 newBugFix
# The newBugFix branch points to the current HEAD
# to verify this:
$ git log -1 newBugFix --format=format:%H
25fe20b2dbb20cac8aa43c5ad64494ef8ea64ffc
# edit branch description
$ git branch --edit-description newBugFix
# Add description in a newly opened editor
Refactoring the Hydro controller 

The hydro controller code is currently horrible needs to be refactored.  
# Show the description
$ git config --get branch.newBugFix.description 
Refactoring the Hydro controller 

The hydro controller code is currently horrible and needs to be refactored.  
# Show the commit hash the new branch based on
$ cat .git/refs/heads/newBugFix 
25fe20b2dbb20cac8aa43c5ad64494ef8ea64ffc

由此可见，该 ID 与当前 HEAD 的 ID 一致。

注意：新建分支后，要切换到该分支才能使用：git checkout -b <newBranch>

拓展：若不从 HEAD 新建分支，而是某个提交 ID（979e346），此时基于该版本的提交可以写作：

# new branch from commit ID
$ git branch anotherBugFix 979e346 
$ git log -1 anotherBugFix --format=format:%h 
979e346 
$ git log -1 anotherBugFix --format=format:%H 
979e3467112618cc787e161097986212eaaa4533 
# checkout new branch
$ git checkout -b lastBugFix 979e346

查看分支信息：

git branch：仅分支名称
git branch -v：在 1 的基础上带注释及简化 SHA-1
git branch -vv：在 2 的基础上展示远程跟踪分支名称

$ git branch -v 

  anotherBugFix 979e346 Interactive Rebase: Do actions if  
* lastBugFix    979e346 Interactive Rebase: Do actions if  
  master        25fe20b Add missing package import for jg 
  newBugFix     25fe20b Add missing package import for jg
$ git branch -vv 

  anotherBugFix 979e346 Interactive Rebase: Do actions if e 
* lastBugFix    979e346 Interactive Rebase: Do actions if e 
  master        25fe20b [origin/master] Add missing package  
  newBugFix     25fe20b Add missing package import for g

3.2 远程分支

有时，本地代码很可能从克隆别人的代码库产生。此时，本地代码就拥有一个远程仓库，通常又叫 origin 源。认识 Git 及其远程代码库，可以从 git status 命令开始：

$ git checkout -b remoteBugFix --track origin/stable-3.2
Switched to a new branch 'remoteBugFix'
Branch 'remoteBugFix' set up to track remote branch 'stable-3.2' from 'origin'.

可见，remoteBugFix 分支的远程跟踪分支为 origin/stable-3.2。这时 git status 的结果，展示的是本地 HEAD 与远程 HEAD 之间，本地是否可以快进到远程分支上。示例如下：

# Find a commit on remote branch
$ git log -10 origin/stable-3.2 --oneline
# Checkout specific SHA-1
$ git reset --hard 2e0d178
HEAD is now at 2e0d17885 Add recursive variant of Config.getNames() methods
# Use 'git status' to see the free benefit of Git
$ git status
On branch remoteBugFix
Your branch is behind 'origin/stable-3.2' by 9 commits, and can be fast-forwarded.
  (use "git pull" to update your local branch)

nothing to commit, working tree clean

注意：

这里有个经常出现的概念：fast-forward，是指 Git 可以不用合并就能将 HEAD 移动到最新的版本上；
git pull 命令其实是两个命令的组合：
1. git fetch
2. git merge（合并远程跟踪分支到本地分支）

执行上述 git status 命令，是用来模拟本地执行 git fetch 后，远程分支上的新内容已经被拉取到本地跟踪分支 origin/stable-3.2 上的状态。继续合并将实际同步到本地分支上：

$ git merge origin/stable-3.2
Updating 2e0d17885..f839d383e
Fast-forward
 .../org/eclipse/jgit/api/RebaseCommandTest.java    | 213 +++++++++++++++++----
 .../src/org/eclipse/jgit/api/RebaseCommand.java    |  31 +--
 .../jgit/errors/IllegalTodoFileModification.java   |  59 ++++++
 .../eclipse/jgit/lib/BaseRepositoryBuilder.java    |   2 +-
 .../src/org/eclipse/jgit/lib/Config.java           |   2 +
 .../src/org/eclipse/jgit/lib/RebaseTodoLine.java   |  16 +-
 6 files changed, 266 insertions(+), 57 deletions(-)
 create mode 100644 org.eclipse.jgit/src/org/eclipse/jgit/errors/IllegalTodoFileModification.java

根据执行结果可知，正如 git status 的提示所言，此次合并是一个快进式合并（fast-forward merge）

除了在创建本地分支时用 --track 指定远程跟踪分支，git 还支持在现有分支上指定远程分支。如果提前创建了本地分支而忘记关联远程分支，git 的这一后期绑定功能就派上用场了：

# Checkout a new branch without relating to its remote tracking branch
$ git checkout -b remoteBugFix2 2e0d17 
Switched to a new branch 'remoteBugFix2' 
# Set the tracking branch manually by using -u or --set-upstream-to
$ git branch --set-upstream-to origin/stable-3.2 
Branch remoteBugFix2 set up to track remote branch stable-3.2 from origin. 
# Validate current status
$ git status 
On branch remoteBugFix2 
Your branch is behind 'origin/stable-3.2' by 9 commits, and can be fast-forwarded. 
  (use "git pull" to update your local branch) 
nothing to commit, working directory clean 
# Same as the previous demo as expected.
# Update the branch (also a fast-forward merge with origin/stable-3.2)
$ git pull 
Updating 2e0d17885..f839d383e
Fast-forward
 .../org/eclipse/jgit/api/RebaseCommandTest.java    | 213 +++++++++++++++++----
 .../src/org/eclipse/jgit/api/RebaseCommand.java    |  31 +--
 .../jgit/errors/IllegalTodoFileModification.java   |  59 ++++++
 .../eclipse/jgit/lib/BaseRepositoryBuilder.java    |   2 +-
 .../src/org/eclipse/jgit/lib/Config.java           |   2 +
 .../src/org/eclipse/jgit/lib/RebaseTodoLine.java   |  16 +-
 6 files changed, 266 insertions(+), 57 deletions(-)
 create mode 100644 org.eclipse.jgit/src/org/eclipse/jgit/errors/IllegalTodoFileModification.java
# The output is still the same as previous one as expected.
# Validate the current HEAD with origin/stable-3.2
$ git log -1 origin/stable-3.2  --format=format:%h
f839d383e
# Still the same.

3.3 强制生成合并提交

在阅读本书之前，您可能已经看过很多软件交付链和分支模型的案例了；您也很可能一直在尝试不同的策略，最后却发现一旦某工具支持特定的工作流后，就很难完全满足您要的其他应用场景了。而 Git 支持几乎所有工作流场景。通常的需求是在合并某个特性时要能生成一次合并提交（即便可以通过快进模式来并入新特性）。这样的需求常用来表示某个特性已被合并，并且希望将这次合并操作显式存到仓库中。

小贴士

鉴于 Git 提供了一套方便快捷的方法来访问所有的提交信息，Git 库其实应该用作日志，而不仅仅是对源代码的备份。

以下示例将生成一次强制合并提交：

# Checkout branch stable-3.1 as remoteOldBugFix for use
$ git checkout -b remoteOldBugFix --track origin/stable-3.1
# force a merge commit
$ git merge origin/stable-3.2 --no-ff --edit --quiet

注意，使用 --edit 参数后，可以在打开的编辑器中修改默认的合并提交注释信息。示例中的 --no-ff 表示禁用快进模式；--quiet 用于简化屏幕输出内容。最终的效果如图所示：

图 3-1

为了与常规方式进行对比，执行合并时删除 --no-ff 参数项：

# Reset to initial status
$ git reset --hard  remotes/origin/stable-3.1
# Merge with fast forward by default
$ git merge origin/stable-3.2 --quiet

效果如下：

图 3-2

中途干预合并内容

除了执行完整合并，Git 还允许用户对合并内容进行干预，自主决定哪些内容参与合并。使用 --no-commit 参数，git 会在合并提交前中断进程，让用户在最终提交前修改或添加文件。例如，项目的特性分支中修改了项目版本号，但主分支并未修改。默认的合并操作会将版本号一并更新为特性分支上的版本号，而实际上你并不希望动版本号。这时使用 --no-commit 就可以避免。

以下示例将对用户干预下的合并操作进行演示。在合并时希望手动剔除更新许可文件那次提交：

# Clone repo into demo
$ git clone https://github.com/PacktPublishing/Git-Version-Control-Cookbook-Second-Edition_hello_world_flow_model.git demo
$ cd demo
# Checkout remote branch
$ git checkout -b remotePartlyMerge --track origin/release/1.0
Branch remotePartlyMerge set up to track remote branch release/1.0 from origin. 
Switched to a new branch 'remotePartlyMerge'
# Force a merge commit with --no-commit flag
$ git merge origin/master  --no-ff --no-commit
Automatic merge went well; stopped before committing as requested
# Exclude LICENSE file
$ git reset LICENSE
# Resume merging
$ git commit -m "Merging without LICENSE"
[remotePartlyMerge 1202b0e] Merging without LICENSE
# Check status (only LICENSE file remain untracked)
$ git status
On branch remotePartlyMerge
Your branch is ahead of 'origin/release/1.0' by 6 commits.
  (use "git push" to publish your local commits)

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

nothing added to commit but untracked files present (use "git add" to track)
# check difference excluding LICENSE file (only on Linux)
$ git diff origin/master !(LICENSE)

考虑到网速问题，已将示例仓库 Git-Version-Control-Cookbook-Second-Edition_hello_world_flow_model.git 添加到本学习库中（ repos/ex3.3-no-commit-repo.rar ）

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