Re: Problem with git diff

From: Bryan Turner <bturner@atlassian.com>
To: Elijah Newren <newren@gmail.com>
Cc: "McRoberts, John" <John.McRoberts@ga.com>,
	"git@vger.kernel.org" <git@vger.kernel.org>
Subject: Re: Problem with git diff
Date: Tue, 9 Jul 2019 16:29:55 -0700	[thread overview]
Message-ID: <CAGyf7-FeAJwWuhu-Zkccsfrcbbf3tuuOWwobsa4OOK1=hWackg@mail.gmail.com> (raw)
In-Reply-To: <CABPp-BE1fQs99ipi9Y8gfQO3QHkxzQhn1uriEbj6YjdYH839eQ@mail.gmail.com>

On Tue, Jul 9, 2019 at 4:13 PM Elijah Newren <newren@gmail.com> wrote:
>
> Hi John,
>
> On Tue, Jul 9, 2019 at 3:57 PM McRoberts, John <John.McRoberts@ga.com> wrote:
> >
> > I am responsible for generating a list of all files changed between two
> > successive releases of software. I was using 'git diff' but have run into a
> > problem.
> >
> > Consider the following situation: A development branch comes off of commit A
> > and files are changed three times.  A tag (REL1) is placed on the third
> > commit.  Then the branch is merged back to master.  At this point, master's
> > HEAD is at C (and it remains there).  Two development branches are created
> > off of master, the first of which is not important here.  In the second one,
> > there are files changed and a tag (REL2) applied.
> >
> >
> > ---------------------[I]
> >
> > /      {dev branch}
> >
> > /
> >
> > /
> >              {master branch}
> > /
> >  [A] ---------------------------------[B]------------------------------->[C]
> > master <HEAD>
> >    \                               filelist 6                           /  \
> >     \                                                                  /
> > \
> >      \                                                                /
> > \
> >       \                                                              /
> > \
> >        \                {development branch}                        /
> > \
> >         \------->[D]----------------------->[E]-------------------[F]
> > \------[G]--------[H]
> >                                                                  REL1
> > REL2
> >                 fileset 1               fileset 2           fileset 3
> > fileset 4    fileset 5
> >
> > At this point, I run
> >     'git diff  -m --first-parent --pretty=fuller --decorate=short
> > --name-only REL2..REL2'
>
> Wow, we really, really need to throw errors and warnings when people
> use crazy range operators with diff.[1][2]  What version of git are
> you using that accepts --decorate=short as an argument to `git diff`?
> And why in the world does git diff accept --first-parent or
> --pretty=fuller?!?  That's insane for git-diff to swallow that.
> (#leftoverbits?)  Also, I think you meant `REL1` one of the two times
> you wrote `REL2`, which makes me suspect you may have done some
> copy-edit-paste and didn't try this actual command.
>
> > I expect to see only filesets 4 and 5 listed.  I also see filesets 1, 2 and
> > 3 showing up.  This means that the git diff command is showing files that,in
> > fact, did not change between the two tags.  By the way, I verified with a
> > file by file comparison that under REL2 and REL1, the files represented by
> > filesets 1, 2 and 3 had identical contents.
>
> From your description, I assume you actually ran something like
>   git diff --name-only REL1..REL2

Did you mean REL1...REL2 (3 dots)? 2 dots (REL1..REL2) is identical to
no dots (REL1 REL2), per the documentation for "git diff":

       git diff [<options>] <commit> <commit> [--] [<path>...]

           This is to view the changes between two arbitrary <commit>.

       git diff [<options>] <commit>..<commit> [--] [<path>...]

           This is synonymous to the previous form. If <commit> on one
side is omitted, it will have the same effect
           as using HEAD instead.

(Forgive me if I'm mistaken here!)

>
> which compares REL2 to the merge base of REL1 and REL2 (yes, this is
> totally counter-intuitive to a large percentage of the git userbase,
> but it is well documented and hard to change).  Also from your
> description, what you seem to want is
>   git diff --name-only REL1 REL2
>
> since you want to compare the two endpoints.  Does that help get what you want?
>
> Hope that helps,
> Elijah
>
> [1] https://public-inbox.org/git/CABPp-BECj___HneAYviE3SB=wU6OTcBi3S=+Un1sP6L4WJ7agA@mail.gmail.com/
> [2] https://public-inbox.org/git/CABPp-BGg_iSx3QMc-J4Fov97v9NnAtfxZGMrm3WfrGugOThjmA@mail.gmail.com/