Re: Problem with git diff

From: Elijah Newren <newren@gmail.com>
To: Bryan Turner <bturner@atlassian.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 16:35:38 -0700	[thread overview]
Message-ID: <CABPp-BETbfzjUyYu9g83=u+HN9r3jwpK538EcOEiawBLG=uwDA@mail.gmail.com> (raw)
In-Reply-To: <CAGyf7-FeAJwWuhu-Zkccsfrcbbf3tuuOWwobsa4OOK1=hWackg@mail.gmail.com>

On Tue, Jul 9, 2019 at 4:30 PM Bryan Turner <bturner@atlassian.com> wrote:
>
> 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!)

Yes, thanks.  In trying to explain how two and three dots behave
contrary to expectation for git diff, I mess up two versus three dots.
That's kind of embarrassing...

> > 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

...though at least I was smart enough to suggest something without
dots, which is the only sane way to use git-diff.  ;-)