Re: git pull fails with merge conflicts. How can this possibly happen?

[David Caldwell]

On 11/14/14 10:37 AM, Alan Mackenzie wrote:
> Hello, Emacs.
> 
> I've now advanced from my last puzzlement.  It turns out that "git
> clone" doesn't properly initialise the new repository.  I had to do this
> manually with "git checkout emacs-24".

Git checkout looks for a branch with the name "emacs-24", failing that
it looks for one matching that in your remotes/* and copies that branch
into "emacs-24". Thus remotes/origin/emacs-24 should be copied to
emacs-24 (and you can check this in the .git/refs/* directory tree +
.git/packed-refs file—it's all text).

> This "git pull" leaves a mass of merge conflicts.  How can this be?
> What does git pull actually do?  The git pull man page says:
>
>   "Incorporates changes from a remote repository into the current
>    branch. In its default mode, git pull is shorthand for git fetch
>    followed by git merge FETCH_HEAD."

The man page is correct.

>   address@hidden ~/emacs/emacs.git/emacs-24 $ git branch -a
>   * emacs-24
>     master
>     remotes/origin/HEAD -> origin/master
>     remotes/origin/emacs-24
>     remotes/origin/master
>   address@hidden ~/emacs/emacs.git/emacs-24 $ git pull

This is the "git fetch" part of "git pull":

>   remote: Counting objects: 32, done.
>   remote: Compressing objects: 100% (16/16), done.
>   remote: Total 32 (delta 26), reused 22 (delta 16)
>   Unpacking objects: 100% (32/32), done.
>   From /home/acm/emacs/emacs.git/master/.

This is the "git merge" part:

>    + 911ad4a...6688117 emacs-24   -> origin/emacs-24  (forced update)

The problem is the 911ad4a. If you look at that commit it is on the
master branch. This implies that your local emacs-24 branch was not
*really* the emacs-24 branch (Maybe you accidentally did "git checkout
-b emacs-24"?).

Git matched the "emacs-24" name to the "origin/emacs-24" and merged that
in, but since your emacs-24 branch was was really just master you got a
bunch of merge conflicts.

That is my guess anyway, it's hard to tell without seeing your repo. If
you "git reset" then "git log", which commit is first? If it's the
911ad4a then you aren't really on the emacs-24 branch.

You can try poking around with gitk to see how the branches interact. I
also quite like the "tig" tool (not part of git)—it's sort of a curses
version of gitk.

-David

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