In cd_to_toplevel, instead of 'cd $(unset PWD; /bin/pwd)/$path'
use 'cd -P $path'.  The "-P" option yields a desirable similarity to
C chdir.

While the "-P" option may be slightly less commonly supported than
/bin/pwd, it is more concise, better tested, and less error prone.
I've already added the 'unset PWD' to fix the /bin/pwd solution on
BSD; there may be more edge cases out there.

This still passes all the same test cases in t5521-pull-symlink.sh and
t2300-cd-to-toplevel.sh, even before updating them to use 'pwd -P'.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

On Mac OS X and possibly BSDs, /bin/pwd reads PWD from the environment if
available and shows the logical path by default rather than the physical
one.

Unset PWD before running /bin/pwd in both cd_to_toplevel and its test.

Still use the external /bin/pwd because in my Bash on Linux, the builtin
pwd prints the same result whether or not PWD is set.
Signed-off-by: NMarcel M. Cary <marcel@oak.homeunix.org>
Tested-by: Wincent Colaiuta <win@wincent.com> (on Mac OS X 10.5.5)
Tested-by: Marcel Koeppen <git-dev@marzelpan.de> (on Mac OS X 10.5.6)
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

I want directories of my working tree to be linked to from various
paths on my filesystem where third-party components expect them, both
in development and production environments.  A build system's install
step could solve this, but I develop scripts and web pages that don't
need to be built.  Git's submodule system could solve this, but we
tend to develop, branch, and test those directories all in unison, so
one big repository feels more natural.  We prefer to edit and commit
on the symlinked paths, not the canonical ones, and in that setting,
"git pull" fails to find the top-level directory of the repository
while other commands work fine.

"git pull" fails because POSIX shells have a notion of current working
directory that is different from getcwd().  The shell stores this path
in PWD.  As a result, "cd ../" can be interpreted differently in a
shell script than chdir("../") in a C program.  The shell interprets
"../" by essentially stripping the last textual path component from
PWD, whereas C chdir() follows the ".." link in the current directory
on the filesystem.  When PWD is a symlink, these are different
destinations.  As a result, Git's C commands find the correct
top-level working tree, and shell scripts do not.

Changes:

* When interpreting a relative upward (../) path in cd_to_toplevel,
  prepend the cwd without symlinks, given by /bin/pwd
* Add tests for cd_to_toplevel and "git pull" in a symlinked
  directory that failed before this fix, plus contrasting scenarios
  that already worked
Signed-off-by: NMarcel M. Cary <marcel@oak.homeunix.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>