From: Francis Moreau <francis.moro@gmail.com>
Date: Thu, 21 Dec 2006 12:24:32 GMT
Subject: Re: Updated Kernel Hacker's guide to git
Message-ID: <38b2ab8a0612210424o4ec5fcd5kb5086c52ccd76491@mail.gmail.com>

Hi,

[ sorry for breaking up the thread but I'd like to fully
  understand that point and I just subscribed to git mail
  list... ]

Linus Torvalds wrote:
>
> On Wed, 20 Dec 2006, Jay Cliburn wrote:
>> $ git diff $(git merge-base master driver)..driver
>
> Be careful. This ONLY works if you don't have criss-cross merges etc, so
> you need to be somewhat careful about it. If you end up having a complex
> merge history between the origin branch and your development tree, things
> will stop working
>
> So it's actually worth understanding what the above does.
>
> Here's the picture to keep in mind: you started off with something like
> this:
>
> 	<- older			newer ->
>
> 	..--A---B---C---D
>
> where the top commit was D, and you started doing your own work off there.
> However, the tree you are tracking (doing "git fetch origin" or somethng)
> ALSO continues, so soon enough you'll have a history that looks like
>
> 	<- older			newer ->
>
> 	..--A---B---C---D---E---F---G---H <-"origin"
> 	                 \
> 	                  --X---Y---Z <- your "driver" branch"
>
> where your work is the "X-Y-Z" sequence.
>
> How, the reason you must NOT do
>
> 	git diff origin..driver
>
> or something like that, is that it will LITERALLY do a diff between those
> two heads. And while that is a perfectly normal diff, it's not what you
> want: it's the diff between the up-stream work and yours, and it will show
> that a lot of work has _not_ happened in your branch (all the E-F-G-H
> stuff), and then you've added some work (X-Y-Z).

I must really miss something but is a diff between origin and driver heads
achieved by:

	$ git diff driver origin

instead of:

	$ git diff origin..driver

?

>From the git-rev-list documentation I can read that:

	git-rev-list origin..driver == git-rev-list driver ^origin

I assume it's still true for git-diff. And the documentation says that
the above command "lists all the commits which are included in driver,
but not in origin".

So all commits included in driver are: (A-B-C-D-X-Y-Z)
all commits included in origin are: (A-B-C-D-E-F-G-H)

All the commits which are included in driver, but not in origin are:
(X-Y-Z), which is definitely not what you claimed.

I know that I'm wrong, so please shed some light in my stupid brain.

-- 
Francis