cache status after git pull

Aha ... is this the problem that caught me out last week (when I ended up with 10 extra files attached to one of my commits)? At the time the blame was placed on a failed merge not being backed out correctly. But I only had the failed merge because "get checkout" had failed to switch branches (and not provided an exit code to stop my script from trying the merge).

Here's what I did this morning.

1) Updated my "linus" branch:

  $ git checkout linus && git pull linus

This appeared to work just fine ... except that when I check the status of my tree I see:

  $ git status
  #
  # Updated but not checked in:
  #   (will commit)
  #
  #       modified: arch/ia64/pci/pci.c
  #       modified: arch/ppc64/kernel/setup.c
  #       modified: arch/sparc64/kernel/pci.c
  #       modified: arch/x86_64/defconfig
  #       modified: drivers/block/cfq-iosched.c
  #       modified: include/asm-m68k/page.h
  #       modified: kernel/cpuset.c
  #
  #
  # On branch refs/heads/linus
  
Which looks like a set of landmines just waiting for me to
step on them!

Today these didn't bite me. "git checkout release" worked and switched to my release branch (and git status went back to saying "nothing to commit"). But in the past I think this is the situation that has caused "git checkout" to fail with the "fatal: Entry 'blah' would be overwritten by merge. Cannot merge."

-Tony

tony.luck@intel.com writes:

Plausible.

I would assume that just after "git checkout linus" before "git pull linus", running "git diff -r linus" would have said nothing.

The second command, "git pull linus", would internally run "git fetch linus". It depends on how your shorthand "linus" is defined, but if it is set to update (either overwrite or fast-forward) the "linus" branch head, then your HEAD pointer would be updated without updating the index and working tree. This is bad because now you are telling git that your working tree is based on updated "linus" branch head, and what you _could_ commit on top of it is the same thing as what old "linus" branch head commit used to have. That's why "git status" output shows the minefield.

If I keep copies of foreign brahches in $GIT_DIR/refs/heads/ somewhere, I never checkout those branches in my working tree. I always stay in my branches to do my work. I may "diff" against them to see where I am. Of course I would "resolve" with them when I feel I am ready.

So, assumes that "linus" short-hand is set up to update $GIT_DIR/refs/heads/linus with the foreign branch head, the above example would have been:

    $ git checkout master && git pull linus
    : examine diffs and be convinced what Linus does is always right.

If my "master" branch is not ready to merge from Linus but I want to get a feel of what is coming, I would instead do:

    : while staying on my master branch
    $ git fetch linus
    $ gitk linus master ;# or git show-branch linus master

and later when my branch is ready, I would merge it into my master:

    : still staying on my master branch
    $ git pull . linus

If you did the pull into your master but it turns out that the merge result is too messy, you could always reset (back to the first example):

    $ git checkout master && git pull linus
    : if merge failed...
    $ git reset --hard master

    $ git checkout master && git pull linus
    : merge succeeds, but I realize that my tree was not quite
    : ready to merge from linus -- going back to pre-merge state
    $ git reset --hard master^1

The rules for updating $GIT_DIR/refs/ when fetch happens have been extended and clarified in 0.99.5 quite a bit.

To set up "linus" short-hand to be updated with "master" branch head from Linus, you would do one of the following:

  * Using old style shorthand

    $ echo >$GIT_DIR/branches/linus \
    http://www.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git/
    $ git fetch linus

  * Using new style shorthand

    $ cat >$GIT_DIR/remotes/linus \
    URL: http://www.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git/
    Pull: master:linus
    $ git fetch linus

  * From the command line, having either branches/linus or
    remotes/linus from the above two examples:

    $ git fetch linus master:linus

To set up "linus" short-hand _not_ to update any local branch head (i.e. you only use "pull" to update your local branch, which can be named "linus" branch), you would do one of the following:

  * Using old style shorthand

    There is no way to do this using old style shorthand without
    an explicit command line <refspec>.  See the "From the
    command line" example below how to do this.

  * Using new style shorthand

    $ cat >$GIT_DIR/remotes/linus \
    URL: http://www.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git/
    Pull: master:
    $ git fetch linus

  * From the command line, having either branches/linus or
    remotes/linus from the above two examples:

    $ git fetch linus master: