Re: [BUG?] HEAD detached at HEAD

From: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Date: Sep 18, 2015, 19:09 UTC
Message-ID: <vpqlhc3h7e7.fsf@anie.imag.fr>
In-Reply-To: <CAGZ79kZxAwMvv6UoZLBd2wTOdj1DFWKQqSPBYL449KSokA8DQQ@mail.gmail.com>

Stefan Beller <sbeller@google.com> writes:

Show 17 quoted lines

> On Fri, Sep 18, 2015 at 10:23 AM, Matthieu Moy
> <Matthieu.Moy@grenoble-inp.fr> wrote:
>> Jacob Keller <jacob.keller@gmail.com> writes:
>>
>>> On Fri, Sep 18, 2015 at 9:59 AM, Matthieu Moy
>>> <Matthieu.Moy@grenoble-inp.fr> wrote:
>>>> I'm getting it even if there's a tag and/or a branch pointing to the
>>>> same commit.
>>>>
>>>> Any idea what's going on?
>>>
>>> Any chance you accidentally made a branch or tag named HEAD?
>>
>> Nice try ;-), but no:
>
> I was playing around with origin/master and origin/pu and
> I cannot reproduce this bug.

I investigated a bit more. The root of the problem is "git checkout --detach" and the reflog. Here's a reproduction script:

rm -fr test-repo git init test-repo cd test-repo echo foo>bar; git add bar; git commit -m "foo" echo boz>bar; git add bar; git commit -m "boz" git checkout --detach git status git branch rm -fr .git/logs/ git status git branch

The end of the output is:

  + git checkout --detach
  + git status
  HEAD detached at HEAD
  nothing to commit, working directory clean
  + git branch
  * (HEAD detached at HEAD)
    master
  + rm -fr .git/logs/
  + git status
  Not currently on any branch.
  nothing to commit, working directory clean
  + git branch
  * (no branch)
    master

If one replaces "git checkout --detach" with "git checkout HEAD^0", then the output is the one I expected:

  HEAD detached at cb39b20

The guilty line in the reflog is:

  checkout: moving from master to HEAD

One possible fix is to resolve HEAD when encountering it in the reflog, like this:

--- a/wt-status.c
+++ b/wt-status.c
@@ -1319,6 +1319,13 @@ static int grab_1st_switch(unsigned char *osha1, unsigned char *nsha1,
        hashcpy(cb->nsha1, nsha1);
        for (end = target; *end && *end != '\n'; end++)
                ;
+       if (!memcmp(target, "HEAD", end - target)) {
+               /* Don't say "HEAD detached at HEAD" */
+               unsigned char head[GIT_SHA1_RAWSZ];
+               get_sha1("HEAD", head);
+               strbuf_addstr(&cb->buf, find_unique_abbrev(head, DEFAULT_ABBREV));
+               return 1;
+       }
        strbuf_add(&cb->buf, target, end - target);
        return 1;
 }

What do you think?

Shall I turn this into a proper patch?

Thanks,

-- 
Matthieu Moy
http://www-verimag.imag.fr/~moy/