Re: git fetch refs and tags

[Johan Herland <johan@herland.net>]

On Tue, Apr 23, 2013 at 4:59 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Jan Weitzel <J.Weitzel@phytec.de> writes:
>
>> Hello,
>> I have the following problem: I have 2 bare git repositories one has
>> several branches and tags.
>> If I try this in the second repository:
>> git fetch -f ../main.git refs/heads/master:refs/heads/master
>> I'm getting also tags from other branches, if I have an old object from
>> one of the other branches.
>> I would expect to have only tags pointing to master ref.
>
> A tag that points at a commit that is reachable from 'master' will
> be followed, not just pointing _at_ 'master'.  For example, when
> your 'master' is a bit beyond v1.2 release, it is likely you will
> also get v1.1 and v1.0 tags (if your release structure is such that
> new release contains everything old releases had).

That is all true, and behaves as expected. However, what Jan is observing
is (I believe) equivalent to the following:

Remote repo:

  o---o---o---o <---- master, tag: spam
   \      ^---- tag: eggs
    \
     o---o---o <---- tag: sausage

Local repo:

  o---o
   \  ^---- master
    \
     o---o---o (unreachable)

Now, when Jan fetches master, he gets the new master, plus tags spam and
eggs (as expected), but he ALSO gets tag sausage, which he _shouldn't_
get, since it is not reachable from master (hence not part of the fetched
history). The following session demonstrates the problem using the above
example:

# Prepare history in repo1
$ git init repo1
Initialized empty Git repository in /home/johan/git/repo1/.git/
$ cd repo1/
$ echo foo>foo
$ git add foo
$ git commit -m a
[master (root-commit) 92f92ec] a
 1 file changed, 1 insertion(+)
 create mode 100644 foo
$ echo bar >> foo
$ git commit -am b
[master e90d835] b
 1 file changed, 1 insertion(+)
$ echo baz >> foo
$ git commit -am c
[master 09e4bb2] c
 1 file changed, 1 insertion(+)
$ echo xyzzy >> foo
$ git commit -am d
[master 13ce4fb] d
 1 file changed, 1 insertion(+)
$ git checkout -b side HEAD~3
Switched to a new branch 'side'
$ echo side >> foo
$ git commit -am side
[side 7294fc9] side
 1 file changed, 1 insertion(+)

# Copy history to repo2, and make most of it unreachable
$ cd ..
$ git clone repo1 repo2
Cloning into 'repo2'...
done.
$ cd repo2/
$ git checkout -b master origin/master~2
Switched to a new branch 'master'
$ git remote rm origin
$ git branch -D side
Deleted branch side (was 7294fc9).
$ git show-ref
e90d8356350e4f2fd5e7bfb3a0327e2fa6115c2a refs/heads/master

# Create tags in repo1
$ cd ../repo1/
$ git checkout master
Switched to branch 'master'
$ git tag spam master
$ git tag eggs master^
$ git tag sausage side
$ git branch -D side
Deleted branch side (was 7294fc9).
$ git show-ref
13ce4fbc1761562a36f755b081b0d44b657c25a9 refs/heads/master
09e4bb21112b0f0acb82ed3b0fd6af9c685c3799 refs/tags/eggs
7294fc90fc1fbd1dd941c8999518d4a4b57048b4 refs/tags/sausage
13ce4fbc1761562a36f755b081b0d44b657c25a9 refs/tags/spam

# Fetch master into repo2
$ cd ../repo2
$ git checkout -b foo
Switched to a new branch 'foo'
$ git fetch -f ../repo1 refs/heads/master:refs/heads/master
From ../repo1
   e90d835..13ce4fb  master     -> master
 * [new tag]         eggs       -> eggs
 * [new tag]         sausage    -> sausage
 * [new tag]         spam       -> spam

# See that tag sausage was fetched even though it's not reachable from master
$ git show-ref
e90d8356350e4f2fd5e7bfb3a0327e2fa6115c2a refs/heads/foo
13ce4fbc1761562a36f755b081b0d44b657c25a9 refs/heads/master
09e4bb21112b0f0acb82ed3b0fd6af9c685c3799 refs/tags/eggs
7294fc90fc1fbd1dd941c8999518d4a4b57048b4 refs/tags/sausage
13ce4fbc1761562a36f755b081b0d44b657c25a9 refs/tags/spam
$ git log --graph --decorate --all --oneline
* 7294fc9 (tag: sausage) side
| * 13ce4fb (tag: spam, master) d
| * 09e4bb2 (tag: eggs) c
| * e90d835 (HEAD, foo) b
|/
* 92f92ec a


Have fun! :)

...Johan

--
Johan Herland, <johan@herland.net>
www.herland.net