[BUG]: git checkout on a new tag with current HEAD shows "head detached" at previous tag

[BUG]: git checkout on a new tag with current HEAD shows "head detached" at previous tag

[Dani Koretsky]

I have 2 tags such as release-17.6.230 and release-17.6.220:
If I'm changing commits, all works as expected.

If however both are pointing to the same commit, the output is as follows:

git checkout release-17.6.220
git status
HEAD detached at release-17.6.220

now if I run:
git checkout release-17.6.230
git status
HEAD detached at release-17.6.220

Which is theoretically correct, but I'd expect after checking out a
certain tag I'd be see that specific tag...

Sorry if this is intended behavior, I couldn't find clear mention of
this behavior on the git checkout documentation online..

Let me know if I can help in anyway.

Cheers,
Dani Koretsky - Researcher

RE: [BUG]: git checkout on a new tag with current HEAD shows "head detached" at previous tag

[Randall S. Becker]

On February 5, 2019 4:20, Dani Koretsky wrote:
> I have 2 tags such as release-17.6.230 and release-17.6.220:
> If I'm changing commits, all works as expected.
> 
> If however both are pointing to the same commit, the output is as follows:
> 
> git checkout release-17.6.220
> git status
> HEAD detached at release-17.6.220
> 
> now if I run:
> git checkout release-17.6.230
> git status
> HEAD detached at release-17.6.220
> 
> Which is theoretically correct, but I'd expect after checking out a certain tag
> I'd be see that specific tag...
> 
> Sorry if this is intended behavior, I couldn't find clear mention of this
> behavior on the git checkout documentation online..

Please use

git checkout -b release-17.6.220

What your  commands above have done is resolved release-17.6.220 to a commit, then checked out that commit instead of creating a branch. Alternatively, use

git checkout -b new-branch release-17.6.220

to name it something else.

Regards,
Randall

-- Brief whoami:
 NonStop developer since approximately 211288444200000000
 UNIX developer since approximately 421664400
-- In my real life, I talk too much.

Re: [BUG]: git checkout on a new tag with current HEAD shows "head detached" at previous tag

[Ævar Arnfjörð Bjarmason]

On Tue, Feb 05 2019, Dani Koretsky wrote:

> I have 2 tags such as release-17.6.230 and release-17.6.220:
> If I'm changing commits, all works as expected.
>
> If however both are pointing to the same commit, the output is as follows:
>
> git checkout release-17.6.220
> git status
> HEAD detached at release-17.6.220
>
> now if I run:
> git checkout release-17.6.230
> git status
> HEAD detached at release-17.6.220
>
> Which is theoretically correct, but I'd expect after checking out a
> certain tag I'd be see that specific tag...
>
> Sorry if this is intended behavior, I couldn't find clear mention of
> this behavior on the git checkout documentation online..
>
> Let me know if I can help in anyway.

You're right about this issue. I haven't dug deep into this, but just
enough to see why this is. When we "git checkout" something we write to
the reflog that we moved to such-and-such a ref, we then consult the
reflog when you run "git status" to see what we detached the HEAD from.

As you can see if you run "git reflog" after you check out the first and
second tag, that entry doesn't change, and we still note just the first
tag you checked out.

This is going to be because of a short-circuit behavior where we see "oh
we already checked this out".

Maybe that needs to be fixed as a bug, but would have more implications,
i.e. are there cases where you can flip-flop and end up spamming the
reflog, should the post-checkout hook run or not in those cases, etc.

Re: [BUG]: git checkout on a new tag with current HEAD shows "head detached" at previous tag

[Ævar Arnfjörð Bjarmason]

On Tue, Feb 05 2019, Ævar Arnfjörð Bjarmason wrote:

> On Tue, Feb 05 2019, Dani Koretsky wrote:
>
>> I have 2 tags such as release-17.6.230 and release-17.6.220:
>> If I'm changing commits, all works as expected.
>>
>> If however both are pointing to the same commit, the output is as follows:
>>
>> git checkout release-17.6.220
>> git status
>> HEAD detached at release-17.6.220
>>
>> now if I run:
>> git checkout release-17.6.230
>> git status
>> HEAD detached at release-17.6.220
>>
>> Which is theoretically correct, but I'd expect after checking out a
>> certain tag I'd be see that specific tag...
>>
>> Sorry if this is intended behavior, I couldn't find clear mention of
>> this behavior on the git checkout documentation online..
>>
>> Let me know if I can help in anyway.
>
> You're right about this issue. I haven't dug deep into this, but just
> enough to see why this is. When we "git checkout" something we write to
> the reflog that we moved to such-and-such a ref, we then consult the
> reflog when you run "git status" to see what we detached the HEAD from.
>
> As you can see if you run "git reflog" after you check out the first and
> second tag, that entry doesn't change, and we still note just the first
> tag you checked out.
>
> This is going to be because of a short-circuit behavior where we see "oh
> we already checked this out".
>
> Maybe that needs to be fixed as a bug, but would have more implications,
> i.e. are there cases where you can flip-flop and end up spamming the
> reflog, should the post-checkout hook run or not in those cases, etc.

To add to this: I think there's a good case to be made that this is
definitely *not* a bug, and changing it would be introducing a bug.

It's 100% true that the "HEAD was detached at" the first first tag to be
checked out, the subsequent "git checkout [other tag]" was a noop.