profile-fast is failing in my Git 2.2.1 build from tar in a Git repo

[Paul Smith <paul@mad-scientist.net>]

Is anyone aware of this?  It seems that profile-fast fails when invoked
from a downloaded tarball, if you are in a Git repository when you
unpack it.

So, for example, I have:

  $ cd $HOME/src
  $ git status
  On branch master
  Your branch is up-to-date with 'origin/master'.

(this is NOT the Git source repo, this is my personal repo containing
scripts used to build various source packages)

Then I download git-2.2.1.tar.xz, unpack it, configure, and run "make
profile-fast".

After it builds everything it starts trying to run the tests, and the
t/perf/run script fails (I added some -x flags in the scripts):

  === Running 9 tests in this tree ===
  cp: cannot stat '/home/psmith/src/git-2.2.1/t/..//home/psmith/src/.git/objects': No such file or directory
  error: failed to copy repository '/home/psmith/src/git-2.2.1/t/..' to '/home/psmith/src/git-2.2.1/t/perf/trash directory.p0000-perf-lib-sanity'

The problem is in the t/perf/perf-lib.sh:test_perf_create_repo_from()
function, where we see this:

  repo="$1"
  source="$2"
  source_git=$source/$(cd "$source" && git rev-parse --git-dir)

The function is invoked as:

  test_perf_create_repo_from '/home/psmith/src/git-2.2.1/t/perf/trash directory.p5302-pack-index' /home/psmith/src/git-2.2.1/t/..

but this doesn't work, because "$source" is not a Git repository; it's
the root of the unpacked tarball.  But when we run "git rev-parse" in
it, it finds the parent Git directory ($HOME/git) and uses that, so the
value of source_git becomes:

  /home/psmith/src/git-2.2.1/t/..//home/psmith/src/.git/objects

which is obviously invalid.  I think you want source_git to be set
something like this:

  source_git=$(cd "$source" && git rev-parse --git-dir || echo "$source")

instead.  There are other ways to do this of course, but this worked for
me... basically we want to use either git rev-parse OR $source but not
both.  I think...?