Re: git: avoiding merges, rebasing

[Benoit SIGOURE]

On Sep 30, 2007, at 4:48 PM, Bruno Haible wrote:

> Hello Jim,
>
> > >   - Did "git pull". It told me:
> >
> > Then (everything is committed), you switch to the trunk and pull
> > (update from public repo) from there:
> >
> >   git checkout master
> >   git pull
> >
> > then go back to your branch and use git-rebase to make your branch
> > change set(s) apply cleanly to the new tip of the trunk:
> >
> >   git checkout branch-B
> >   git rebase master
> >
> > The rebase is where you'll resolve any conflicts.
>
> OK, then my problem was that I did "git pull" without a rebase step.

You shouldn't pull if you want to rebase.  Read man git-pull, it  
clearly states that pull = fetch + merge in current branch.  If you  
want to rebase, you don't want to merge.  That's why you had to solve  
conflicts twice (once for merge, once for rebase).  The resulting  
commit tree will also have an extra commit (that of the merge done by  
git-pull) which is stupid since the goal of rebase is to preserve a  
linear history and have your commits on top of it (so why add merge- 
commits if there is no merge in the end?).

> Remember that I don't like to use "git checkout", because I want to  
> memoize
> my working topic by directory name, and not have git modify my  
> source files
> unnecessarily when I have built object files in the same directory.
>
> In this situation, I wanted to use "git pull" just to update my  
> changes
> and let me reduce conflicts. This is not the moment where I want to  
> start
> bookkeeping (adding files, thinking about a commit message etc.)
>
> $ git checkout master
> M       ChangeLog
> Already on branch "master"
>
> $ git pull
> Updating 61135ee..0f0eb9b
> ChangeLog: needs update
> fatal: Entry 'ChangeLog' not uptodate. Cannot merge.

You can't merge (and thus can't pull) if your tree is not clean.   
Possible solutions:
  1. commit your change if it's ready for commit.
  2. stash your changes away (man git-stash, requires git >= 1.5.3)

I personally use git-stash:
$ git stash
$ git pull / fetch+rebase
<solve conflicts + commit>
$ git stash apply
$ git stash clear # unless you want to keep the stash

> $ git rebase master
> ChangeLog: needs update
>
> What am I supposed to do here?
>   - "git fetch" does too not enough: it only fetches changes but  
> does not
>      store them in my "master" branch.

It stores them in your remote master master IIRC.  pull will simply  
do that + merge in your current branch (which happens to be your  
local master branch).

>   - "git rebase master" without "git add" does nothing;
>     "git rebase master" after "git add" tells me
>     "Current branch master is up to date.".

You must have a pristine tree+index in order to use rebase/merge.


Here is what you should do if you want to achieve what I think you're  
trying to achieve:

$ git branch -a
* master
  origin/HEAD
  origin/master

(if you have color.branch=auto in your conf, you will easily notice  
that origin/* are remote branches while master is local)

$ git fetch
remote: Generating pack...
[...]
100% (3/3) done
* refs/remotes/origin/master: fast forward to branch 'master' of /tmp/ 
foo/ref/
  old..new: 7b910f5..3e9ae50

Now the new commits have been fetched in origin/master (have a look  
at git log: your local branch is unchanged, now have a look at git  
log origin/master, the new commits appeared there).  Now you want to  
preserve linear history, so let's rebase:

$ git stash # If you have a non-committed changes
$ git rebase origin/master
<maybe: solve conflicts, commit>
$ git stash apply # restore your non-committed changes
<maybe: solve conflicts>
$ git stash clear # get rid of the stash

Pitfalls:
  - git stash does not stash untracked files.
    http://marc.info/?l=git&m=119109247220712&w=4
  - git push can push the stashed trees.
    http://marc.info/?l=git&m=119089831513994&w=4
  - Changing branch while having uncommitted changes will work and  
keep the changes (if the merge is not trivial, otherwise it will bail  
out with an error).
    http://marc.info/?l=git&m=118975544126497&w=4

Hope this helps.

Cheers,

--
Benoit Sigoure aka Tsuna
EPITA Research and Development Laboratory

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