Re: Master and origin/master diverged

Hi Phil,

On 22 June 2012 11:34, Phil Hord [off-list ref] wrote:

On Fri, Jun 22, 2012 at 1:53 PM, Hilco Wijbenga
[off-list ref] wrote:

quoted

One of my developers managed to push something that somehow "diverged"
origin/master from everyone else's local master.

A --> B --> C --> D (everybody's local master)
|
\--> B' --> C' --> D' --> E (origin/master)

(i.e., A is the commit where things diverged; everyone's local master
points to D but the new commit (E) that was pushed to origin/master
uses different SHA1s for B, C, and D). I hope I explained it clearly
enough.

Now running git pull creates a merge commit joining D and E.

When I asked the developer what he had done he told me everything had
looked normal. No Git warnings, nothing strange in gitk (i.e. normal
linear history). So I do not understand what went wrong.

Does anyone have any idea as to what might have happened? Perhaps if I
understand how this happened I might be able to prevent it from
happening again.

There are a number of ways this can happen, but they all involve
rewriting history.  Usually that is something your developer would be
aware of doing.  It does not usually happen by mistake.

My thoughts exactly.

Also, in order to push the new E commit, the developer would have to
"force" the push by placing a "+" in front of the references, like
this:

 git push origin +master:master

Is that the same as

git push --force origin master

?

If he used a gui, then I do not know how this option would be spelled,
but it may be called "force" or something else.

AFAIK, he uses the CL for this. No GUI.

You can look at the reflog on the developer's machine to determine
where the new commits came from.  For example, here are some commits I
rebased a few weeks ago in a repository on my machine:

$ git reflog --relative-date
c93b31b HEAD@{6 weeks ago}: checkout: moving from mine to c93b31b
93a357f HEAD@{6 weeks ago}: rebase finished: returning to refs/heads/mine
93a357f HEAD@{6 weeks ago}: rebase: Add a makefile to help me remember
how to make
f804993 HEAD@{6 weeks ago}: rebase: Allow working in multiple branches
c93b31b HEAD@{6 weeks ago}: rebase: Update Gerrit 2.4 ReleaseNotes
5cac09e HEAD@{6 weeks ago}: rebase: Gerrit 2.4 ReleaseNotes
f41a9b4 HEAD@{6 weeks ago}: checkout: moving from mine to
f41a9b447304733a1784ece373723f8622c8dbad^0
879e5d9 HEAD@{6 weeks ago}: rebase finished: returning to refs/heads/mine
879e5d9 HEAD@{6 weeks ago}: rebase: Add a makefile to help me remember
how to make
35d7a48 HEAD@{6 weeks ago}: rebase: Allow working in multiple branches
c7a845a HEAD@{6 weeks ago}: rebase: Update Gerrit 2.4 ReleaseNotes
7b51315 HEAD@{6 weeks ago}: rebase: Gerrit 2.4 ReleaseNotes
d6799b1 HEAD@{6 weeks ago}: checkout: moving from mine to
d6799b1d40ffc5412e4174fd95bd5fb412781537^0
d9bb39b HEAD@{6 weeks ago}: checkout: moving from
d6799b1d40ffc5412e4174fd95bd5fb412781537 to mine
d6799b1 HEAD@{6 weeks ago}: checkout: moving from mine to origin/master
d9bb39b HEAD@{6 weeks ago}: commit (amend): Add a makefile to help me
remember how to make
62097f8 HEAD@{6 weeks ago}: commit: Add a makefile to help me remember
how to make
dfa61e4 HEAD@{6 weeks ago}: checkout: moving from
dfa61e465bcb27f5698c48d1ec9d32e8fd62c604 to mine

bb91ffa HEAD@{87 minutes ago}: checkout: moving from master to viz
bb91ffa HEAD@{88 minutes ago}: checkout: moving from viz to master
bb91ffa HEAD@{2 hours ago}: rebase finished: returning to refs/heads/viz
bb91ffa HEAD@{2 hours ago}: checkout: moving from viz to
bb91ffa3db35852bf6e9b15855421a1c5117b2f2^0
df9529a HEAD@{2 hours ago}: checkout: moving from master to viz
bb91ffa HEAD@{2 hours ago}: pull origin master: Fast-forward
cceee83 HEAD@{2 hours ago}: reset: moving to HEAD~23
df9529a HEAD@{2 hours ago}: checkout: moving from viz to master
df9529a HEAD@{2 hours ago}: checkout: moving from master to viz
df9529a HEAD@{6 hours ago}: checkout: moving from master to master
df9529a HEAD@{18 hours ago}: checkout: moving from master to master
df9529a HEAD@{18 hours ago}: checkout: moving from master to master
df9529a HEAD@{18 hours ago}: reset: moving to
df9529a4249b9de9cc1956283e5210b68acfe507
6633b41 HEAD@{18 hours ago}: pull origin master: Fast-forward
df9529a HEAD@{18 hours ago}: reset: moving to
df9529a4249b9de9cc1956283e5210b68acfe507
6633b41 HEAD@{18 hours ago}: checkout: moving from master to master
6633b41 HEAD@{18 hours ago}: pull origin master: Merge made by the
'recursive' strategy.
df9529a HEAD@{18 hours ago}: checkout: moving from master to master
df9529a HEAD@{18 hours ago}: rebase finished: returning to refs/heads/master
df9529a HEAD@{18 hours ago}: rebase: Fixed some visualization bug,
added resources for new spark visualization, deleted obsolete
resources
8944283 HEAD@{18 hours ago}: rebase: Clean up social-sticky-widget.
f9bc439 HEAD@{18 hours ago}: rebase: Resolve build error
14373e3 HEAD@{18 hours ago}: rebase: Changed social-widget
add-friend-button binding names.
abf30b9 HEAD@{18 hours ago}: rebase: Added social-sticky-widget to the
community lounge.
d01d4da HEAD@{18 hours ago}: rebase: Extend email support.
0a60fe0 HEAD@{18 hours ago}: rebase: Fixed asyncronous text and slowed
plane by 50%. (37.5% slower in total than original speed)
4777fdd HEAD@{18 hours ago}: rebase: Added social-sticky-widget.
e744734 HEAD@{18 hours ago}: rebase: Slowed plane speed down by 25%
and increased the font size.
52137b7 HEAD@{18 hours ago}: rebase: Fixed some graphical glitches
with the plane.
6e60b86 HEAD@{18 hours ago}: rebase: Updated the header and island to
only show nature path in demo.
23c8ccb HEAD@{18 hours ago}: rebase: Added plane to the header and
remove dock from production.
1107a7e HEAD@{18 hours ago}: rebase: Show completed Quests in Activity Summary.
260f8c5 HEAD@{18 hours ago}: rebase: Added dock to header and island swf.
0819d2c HEAD@{18 hours ago}: rebase: [DE575] Change friend bonus percentage.
17685ba HEAD@{18 hours ago}: rebase: Improve level queries.
35d69b4 HEAD@{18 hours ago}: rebase: Refactor Period.
9749d52 HEAD@{18 hours ago}: rebase: Make sure to use correct date range.
180b648 HEAD@{18 hours ago}: rebase: Added fix for images that were
not working in IE8 and cleaned up some commented code.
f94e317 HEAD@{18 hours ago}: checkout: moving from master to
f94e317e82ea939a931cdc691e267e7c64f4dc00^0
38f2bb6 HEAD@{19 hours ago}: commit: Fixed some visualization bug,
added resources for new spark visualization, deleted obsolete
resources
98f2a97 HEAD@{19 hours ago}: pull origin master: Fast-forward
b325a96 HEAD@{32 hours ago}: pull origin master: Fast-forward
f94e317 HEAD@{8 days ago}: checkout: moving from
f884b312dcdb247ddf7eaf7c11eb9ffaab034b40 to master
f884b31 HEAD@{8 days ago}: checkout: moving from master to
f884b312dcdb247ddf7eaf7c11eb9ffaab034b40^0
f94e317 HEAD@{8 days ago}: commit: Fixed visualizations scaling and
integration of nature visualization
5ab4887 HEAD@{8 days ago}: pull origin master: Fast-forward
564abdd HEAD@{9 days ago}: pull origin master: Fast-forward
283c602 HEAD@{11 days ago}: pull origin master: Fast-forward

I have left it in just to be complete but you should ignore everything
"2 hours ago" and more recent. (I fixed the problem and told him to
pull again; the advantage of a small team.)

This leads to 2 new questions.

1) What does "checkout: moving from master to master" mean?
2) I'm guessing the root of the problem is "pull origin master: Merge
made by the 'recursive' strategy."? I do not see a push anywhere,
though.

You can see the new commit SHA-1's on the lines that say "rebase:
<original commit message>"

But there are other ways to rewrite history, such as filter-branch.

Given that *I* do not even really know about that, I doubt he would. :-)

You can also compare the commits to see what the differences are.
This may trigger  the developer's memory about how it might have
happened.

The only differences seem to be the SHA-1s.

Cheers,
Hilco