will git rebase has side effect

will git rebase has side effect

[Yubin Ruan]

Suppose that I have such a history of commit locally:

A --> B --> C --> D

If I then add a few more commits locally

A --> B --> C --> D --> E --> F --> G

And then I do a rebase and squash F and G into one single commit H.
What side effect will this rebase have? How will this affect "git push
origin master"?

Yubin

Re: will git rebase has side effect

[Kevin Daudt]

Forgot to cc the mailing list.

On Sun, Oct 01, 2017 at 09:23:23PM +0800, Yubin Ruan wrote:
> Suppose that I have such a history of commit locally:
> 
> A --> B --> C --> D
> 
> If I then add a few more commits locally
> 
> A --> B --> C --> D --> E --> F --> G
> 
> And then I do a rebase and squash F and G into one single commit H.
> What side effect will this rebase have? How will this affect "git push
> origin master"?
> 
> Yubin

Hello Yubin,

So the situation is this:

            [origin/master]
                  |
A --> B --> C --> D --> E --> F --> G
                                    |
                                 [master] 

Then you squash (F' is the result of squashing F and G):

            [origin/master]
                  |
A --> B --> C --> D --> E --> F'
                              |
                           [master] 

When you want to push now, it's just as if you just created just two
commits in the first place, and you can just push normally (assuming no
one else has pushed in the mean time.

The situation is different when you have pushed already:

                              [origin/master]
                                    |
A --> B --> C --> D --> E --> F --> G
                                    |
                                 [master] 

Then after you squash, the history would look as follows:

                              [origin/master]
                                    |
A --> B --> C --> D --> E --> F --> G
                         \
                          --> F'
                              |
                           [master] 

This sitation would look to git like you created F', and someone else
had pushed F and G. It will reject the push, saying you would need to
merge these changes first (but you don't want this, because you are
merging the same changes together).

To solve this, you can use git push --force-with-lease=master origin,
which will force the push, overwriting the history the remote already
had.

Hope this helps, Kevin.

nb. --force-with-lease is a safer version of just (-f|--force), because
it will prevent you from overwriting history you don't have locally, for
example when someone else did push already.

Re: will git rebase has side effect

[Yubin Ruan]

2017-10-01 22:17 GMT+08:00 Kevin Daudt <me@ikke.info>:
> Forgot to cc the mailing list.
>
> On Sun, Oct 01, 2017 at 09:23:23PM +0800, Yubin Ruan wrote:
>> Suppose that I have such a history of commit locally:
>>
>> A --> B --> C --> D
>>
>> If I then add a few more commits locally
>>
>> A --> B --> C --> D --> E --> F --> G
>>
>> And then I do a rebase and squash F and G into one single commit H.
>> What side effect will this rebase have? How will this affect "git push
>> origin master"?
>>
>> Yubin
>
> Hello Yubin,
>
> So the situation is this:
>
>             [origin/master]
>                   |
> A --> B --> C --> D --> E --> F --> G
>                                     |
>                                  [master]
>
> Then you squash (F' is the result of squashing F and G):
>
>             [origin/master]
>                   |
> A --> B --> C --> D --> E --> F'
>                               |
>                            [master]
>
> When you want to push now, it's just as if you just created just two
> commits in the first place, and you can just push normally (assuming no
> one else has pushed in the mean time.

Hmm..You mean, if I do a squash, it will only affects those commits
that has been squashed, not any other commits, and their parent-child
relations remain the same?

Yubin

> The situation is different when you have pushed already:
>
>                               [origin/master]
>                                     |
> A --> B --> C --> D --> E --> F --> G
>                                     |
>                                  [master]
>
> Then after you squash, the history would look as follows:
>
>                               [origin/master]
>                                     |
> A --> B --> C --> D --> E --> F --> G
>                          \
>                           --> F'
>                               |
>                            [master]
>
> This sitation would look to git like you created F', and someone else
> had pushed F and G. It will reject the push, saying you would need to
> merge these changes first (but you don't want this, because you are
> merging the same changes together).
>
> To solve this, you can use git push --force-with-lease=master origin,
> which will force the push, overwriting the history the remote already
> had.
>
> Hope this helps, Kevin.
>
> nb. --force-with-lease is a safer version of just (-f|--force), because
> it will prevent you from overwriting history you don't have locally, for
> example when someone else did push already.
>
>

Re: will git rebase has side effect

[Kevin Daudt]

On Mon, Oct 02, 2017 at 12:06:38AM +0800, Yubin Ruan wrote:
> 2017-10-01 22:17 GMT+08:00 Kevin Daudt <me@ikke.info>:
> > Forgot to cc the mailing list.
> >
> > On Sun, Oct 01, 2017 at 09:23:23PM +0800, Yubin Ruan wrote:
> >> Suppose that I have such a history of commit locally:
> >>
> >> A --> B --> C --> D
> >>
> >> If I then add a few more commits locally
> >>
> >> A --> B --> C --> D --> E --> F --> G
> >>
> >> And then I do a rebase and squash F and G into one single commit H.
> >> What side effect will this rebase have? How will this affect "git push
> >> origin master"?
> >>
> >> Yubin
> >
> > Hello Yubin,
> >
> > So the situation is this:
> >
> >             [origin/master]
> >                   |
> > A --> B --> C --> D --> E --> F --> G
> >                                     |
> >                                  [master]
> >
> > Then you squash (F' is the result of squashing F and G):
> >
> >             [origin/master]
> >                   |
> > A --> B --> C --> D --> E --> F'
> >                               |
> >                            [master]
> >
> > When you want to push now, it's just as if you just created just two
> > commits in the first place, and you can just push normally (assuming no
> > one else has pushed in the mean time.
> 
> Hmm..You mean, if I do a squash, it will only affects those commits
> that has been squashed, not any other commits, and their parent-child
> relations remain the same?
> 
> Yubin

Only the commits being squashed, and the commits after it (not
applicable in your case). But not commits that come before the squash.
Remember that in git, commits point at their parent(s), not the opposite
way. So if you change commits, only the children will have to change (to
point to the new hashes), but not their parents.