threads / discuss / 20039

Re: Checking for fast-forward

Subject: Re: Checking for fast-forward

## tl;dr

5 messages between Jul 6, 2009 and Jul 8, 2009.

replies: 4people: 3as markdown or json

Florian Mickler· Jul 6, 2009, 21:26 UTC · lore

this is more of a git question, than smth special to msysgit.

(git ml cc'd)

On Mon, 6 Jul 2009 17:36:54 +0100 Lee Griffiths <poddster@gmail.com> wrote:

Show 19 quoted lines

> 
> I have a script that checks for fast-forwarding by doing a git push
> --dry-run. This strikes me as the wrong way to do it as it does _all_
> of the stuff a git push would normally do i.e., packing and so on, and
> I'm only really after the fast-forward check. Seeing as I already do a
> git push at the end of the script (actualy two, as I do a --tags one
> as well[1]), it seems like a big waste of time. Is there anyother way
> to check and see if the git push would work? (I want the script to
> avoid doing a git pull if possible).
> 
> 
> Thanks,
> Lee
> 
> 
> 
> [1] I originally assumed --tags would push the data AND the tags, but
> that doesn't seem to be the case.... Am I wrong in this?
>

Michael J Gruber· Jul 7, 2009, 08:21 UTC · re: Florian Mickler · lore

Florian Mickler venit, vidit, dixit 06.07.2009 23:26:

Show 16 quoted lines

> this is more of a git question, than smth special to msysgit. 
> 
> (git ml cc'd)
> 
> On Mon, 6 Jul 2009 17:36:54 +0100
> Lee Griffiths <poddster@gmail.com> wrote:
> 
>>
>> I have a script that checks for fast-forwarding by doing a git push
>> --dry-run. This strikes me as the wrong way to do it as it does _all_
>> of the stuff a git push would normally do i.e., packing and so on, and
>> I'm only really after the fast-forward check. Seeing as I already do a
>> git push at the end of the script (actualy two, as I do a --tags one
>> as well[1]), it seems like a big waste of time. Is there anyother way
>> to check and see if the git push would work? (I want the script to
>> avoid doing a git pull if possible).

No. (I infer your question is how to find out whether a push is a fast-forward.)

If you don't know the state of the branch head in the remote repo you simply cannot know whether the push will be a fast-forward.

If you know that your corresponding remote branch (say remotes/origin/foo) is up-to-date with the destination branch (say foo) in the remote repo (e.g., because you know you've fetched before and nobody else is allowed to push there) then you can compare your branch to be pushed (say foo) with your remote branch:

If $(git rev-list bar..remotes/origin/foo) is empty then the branch foo in the remote repo can be fast-forwarded to bar.

Chhers, Michael

Florian Mickler· Jul 7, 2009, 10:46 UTC · re: Michael J Gruber · lore

On Tue, 07 Jul 2009 10:21:40 +0200 Michael J Gruber <git@drmicha.warpmail.net> wrote:

Show 5 quoted lines

> If $(git rev-list bar..remotes/origin/foo) is empty then the branch
> foo in the remote repo can be fast-forwarded to bar.
> 
> Chhers,
> Michael

in that case you could also do 'git cherry bar origin/foo'

that shows you all commits that are in origin/foo but not in bar.

Sincerely, Florian

Michael J Gruber· Jul 7, 2009, 11:01 UTC · re: Florian Mickler · lore

Florian Mickler venit, vidit, dixit 07.07.2009 12:46:

Show 13 quoted lines

> On Tue, 07 Jul 2009 10:21:40 +0200
> Michael J Gruber <git@drmicha.warpmail.net> wrote:
> 
>> If $(git rev-list bar..remotes/origin/foo) is empty then the branch
>> foo in the remote repo can be fast-forwarded to bar.
>>
>> Chhers,
>> Michael
> 
> in that case you could also do 
> 'git cherry bar origin/foo'
> 
> that shows you all commits that are in origin/foo but not in bar.

Well, that goes through all commits "bar..remotes/origin/foo" and computes patch-ids. It is porcelain. Don't use it for scripting.

Michael

Lee Griffiths· Jul 8, 2009, 17:36 UTC · re: Michael J Gruber · lore

Thanks for the answers :)

After seeing that git push skips the packing (and potentially other
things) when doing a dry run, and given that:
	git push --dry-run
takes 1.5s on average and that:
	git fetch
	git rev-list master..remotes/origin/master
OR
	git ls-remote origin refs/remotes/origin/master

take 4s on average, I think I'll stick with the dry-run & checking for exception method.

Thanks though :)

2009/7/7 Michael J Gruber <git@drmicha.warpmail.net>:

> If $(git rev-list bar..remotes/origin/foo) is empty then the branch foo
> in the remote repo can be fast-forwarded to bar.