Git同一仓库独立副本间的行为困惑及问题咨询

问题背景 #

我有两个终端，分别指向同一Git仓库的独立副本，均处于master分支的HEAD位置。在终端1中修改文件、提交并推送至远程仓库后，终端2执行git pull却触发了合并操作（尽管此副本未做任何修改）；执行git status后，终端2显示本地master分支比origin/master超前1个提交，提示需推送。若在终端2执行推送，会新增一个提交，git log --graph显示终端1的提交变为分支状。

操作重现 #

终端1操作 #

> cd ~/t1
> git clone git@server:test/test-repository-1.git
> cd test-repository-1
> vim rich1 [...edit an exiting file 'rich1'...]
> git add -u
> git commit
> git push

[注：以上操作无异常输出]

终端2操作 #

> cd ~/t2/
> git clone git@server:test/test-repository-1.git
> cd test-repository-1
> git pull
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 1), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From server:test-repository-1
   75ec9a3..ef01990  master     -> origin/master
Merge made by the 'recursive' strategy.
 rich1 | 1 +
 1 file changed, 1 insertion(+)

> git status
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

终端2推送后的日志 #

> git log --graph
*   826660c (HEAD -> master, origin/master, origin/HEAD) Merge branch 'master' of server:test/test-repository-1
|\  [this is the commit from Terminal 2]
| * ef01990 comment [this was the commit from Terminal 1]
|/
|   M   rich1
<snip>

重复操作验证 #

终端1

<as previous>
> git commit
[master 3f513fe] comment
 1 file changed, 1 deletion(-)

终端2

> git fetch -a; git log --graph --oneline HEAD @{u}
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 1), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From server:test-repository-1
   826660c..3f513fe  master     -> origin/master
* 3f513fe comment
*   826660c Merge branch 'master' of server1:test/test-repository-1
|\  
| * ef01990 comment
|/  
* 75ec9a3 added text to rich1
* 66b1c1b Modified README and added rich1
* a2af0fd comment 1
* 867b6fd mmreadme added
* db4b74f added empty readme file

> git pull
Merge made by the 'recursive' strategy.
 rich1 | 1 -
 1 file changed, 1 deletion(-)

> git log --graph --oneline HEAD @{u}
*   2597513 Merge branch 'master' of spc-git-dev01:git-training/test-repository-1
|\  
| * 3f513fe comment
|/  
*   826660c Merge branch 'master' of spc-git-dev01:git-training/test-repository-1
|\  
| * ef01990 comment
|/  
* 75ec9a3 added text to rich1
* 66b1c1b Modified README and added rich1
* a2af0fd comment 1
* 867b6fd mmreadme added
* db4b74f added empty readme file

核心疑问 #

1. 为何git pull会执行合并而非直接拉取最新版本？
2. 终端2副本已与远程master同步，为何Git判定其超前？这不符合直觉。

配置信息 #

> git config -l
user.email=<snip>
user.name=<snip>
url.https:<snip>
color.ui=true
color.status=true
color.brnch=true
alias.co=checkout
alias.br=branch
alias.dt=difftool
alias.rem=remote
merge.conflictstyle=diff3
merge.tool=vimdiff
merge.ff=false
mergetool.diffconflicts.cmd=nvim -c DiffConflictsWithHistory "$MERGED" "$BASE" "$LOCAL" "$REMOTE"
mergetool.diffconflicts.trustexitcode=true
mergetool.keepbackup=true
mergetool.vimdiff.cmd=nvim -d $MERGED $LOCAL $BASE $REMOTE -c 'wincmd J'
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true
remote.origin.url=<snip>:test-repository-1.git
remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
branch.master.remote=origin
branch.master.merge=refs/heads/master

> git config --global -l
user.email=<snip>
user.name=<snip>
url.https:<snip>
color.ui=true
color.status=true
color.brnch=true
alias.co=checkout
alias.br=branch
alias.dt=difftool
alias.rem=remote
merge.conflictstyle=diff3
merge.tool=vimdiff
merge.ff=false
mergetool.diffconflicts.cmd=nvim -c DiffConflictsWithHistory "$MERGED" "$BASE" "$LOCAL" "$REMOTE"
mergetool.diffconflicts.trustexitcode=true
mergetool.keepbackup=true
mergetool.vimdiff.cmd=nvim -d $MERGED $LOCAL $BASE $REMOTE -c 'wincmd J'

问题解答 #

疑问1：为何git pull执行合并而非直接拉取 #

问题根源是你配置了merge.ff=false——这个设置强制Git禁用快进（Fast-Forward）合并模式。

默认情况下，当本地分支没有新提交时，git pull会采用快进模式：直接将本地分支指针移动到远程分支的最新提交位置，不会生成新的合并提交。但merge.ff=false会让Git无论是否可以快进，都生成一个新的合并提交，把远程分支的提交合并到本地分支，这就是你看到的合并操作。

疑问2：为何Git判定本地分支超前 #

因为git pull生成了一个新的本地合并提交。此时origin/master指向的是终端1推送的远程提交，而本地master指向的是这个新的合并提交，所以Git认为本地分支比远程分支多了1个提交，即“超前1个提交”。

当你推送这个合并提交到远程后，远程仓库就会包含这个合并节点，终端1的提交就会显示为分支状——本质是远程仓库现在有了两条提交路径：一条是终端1的提交链，另一条是终端2生成的合并提交链。

解决方案 #

如果希望恢复默认的快进合并行为，执行以下命令之一：

• 全局生效（所有仓库适用）：git config --global merge.ff true
• 当前仓库生效：git config merge.ff true

这样后续在本地无新提交时执行git pull，就会直接快进更新本地分支，不会生成额外的合并提交。

内容的提问来源于stack exchange，提问作者Rich