RE: Branch information (git branch/status) inconsistent when in detached HEAD state

From: Stijn De Ruyck <stijn.deruyck@onsemi.com>
Date: Oct 7, 2015, 09:57 UTC
Message-ID: <247ABEF3B84FB7499C074A0FE8058694153CB1BE@ONWATER51M.ad.onsemi.com>
In-Reply-To: <5614E0C0.7060805@drmicha.warpmail.net>

Yes it is the tip. So all I'm doing is checking out the exact same commit (the tip of a branch), but in different ways and in different sequences. The result on disk is the same, but the issue is git branch/status doesn't always reflect what I just did...

If I do git checkout origin/develop, git branch might still say "detached at 545a36f", which, while true, feels wrong. How can I know afterwards what branch I actually tried to check out? "Detached at origin/develop" would make that clear. (I use this information in a build script to embed version information (including the branch being built) into the binary.)

Best regards,

Stijn De Ruyck

-----Original Message-----
From: Michael J Gruber [mailto:git@drmicha.warpmail.net] 
Sent: Wednesday, October 07, 2015 11:07 AM
To: Stijn De Ruyck; git@vger.kernel.org
Subject: Re: Branch information (git branch/status) inconsistent when in detached HEAD state

Stijn De Ruyck venit, vidit, dixit 06.10.2015 15:03:

Show 38 quoted lines

> Hello,
> 
> Consider a repository with a develop branch tracking origin/develop and where HEAD = 545a36f = develop = origin/develop.
> Tested with Git 2.4.3 and 1.8.3.4 on Linux.
> 
> 1) git checkout develop
> 2) git branch | head -1 (or git status)
> * develop
> 3) git checkout origin/develop
> Note: checking out 'origin/develop'.
> You are in 'detached HEAD' state.
> 4) git branch | head -1
> * (HEAD detached at origin/develop)
> 5) git checkout 545a36f
> 6) git branch | head -1
> * (HEAD detached at origin/develop)
> 7) git checkout develop
> 8) git branch | head -1 (or git status)
> * develop
> 9) git checkout 545a36f
> Note: checking out '545a36f'.
> You are in 'detached HEAD' state.
> 10) git branch | head -1 (or git status)
> * (HEAD detached at 545a36f)
> 11) git checkout origin/develop
> 12) git branch | head -1 (or git status)
> * (HEAD detached at 545a36f)
> 
> As you can see, checking out a revision by SHA1 after checking out a local branch tells you you are detached at that SHA1. Ok.
> But, checking out a revision by SHA1 after checking out a remote tracking branch tells you you are detached at that remote tracking branch.
> And checking out a remote tracking branch after checking out a revision by SHA1 tells you you are detached at that SHA1.
> 
> This is confusing. Is this by design?
> For a script I am writing, it would be great if the output would be consistent. Checkout origin/develop should always say "detached at origin/develop". Checkout 545a36f should always say "detached at 545a36f".
> 
> It looks like the detached head information is only updated when a detached head state is entered and not anymore when a checkout occurs "within" a detached head state.
> 
> Best regards,

Does 545a36f happen to be the tip (value) of origin/develop?

For a sha1 different from the tip, I can't reproduce the effect that you describe. There have been some changes in related code recently, but I don't think they should affect this scenario.

Michael