[PATCH v2] Makefile: Fix CDPATH problem

[Jonathan Nieder <jrnieder@gmail.com>]

If CDPATH is set, "cd" prints its destination to stdout, causing
the common (cd a && tar cf - .) | (cd b && tar xf -) idiom to fail.
For example:

 make -C templates DESTDIR='' install
 make[1]: Entering directory `/users/e477610/exptool/src/git-1.7.0.2/templates'
 install -d -m 755 '/home/e477610/exptool/share/git-core/templates'
 (cd blt && gtar cf - .) | \
	(cd '/home/e477610/exptool/share/git-core/templates' && umask 022 && gtar xof -)
 gtar: This does not look like a tar archive

Most git scripts already protect against use of CDPATH through
git-sh-setup, but the Makefile doesn’t.

Reported-by: Michael Cox <mhcox@bluezoosoftware.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
> Eh, the rationale and the in-code comment need to be fixed.  The issue is
> not "taking us to random places", but "reporting the name of the random
> place in its standard output".

That makes more sense.  Thanks.

> But other than that, this is something we have seen on the list a few
> times, and I think it is about time to do this.

Here’s an updated patch.

 Makefile |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/Makefile b/Makefile
index 4387d42..98372eb 100644
--- a/Makefile
+++ b/Makefile
@@ -317,6 +317,12 @@ SCRIPT_PYTHON =
 SCRIPT_SH =
 TEST_PROGRAMS =
 
+# Having this variable in your environment would break pipelines because
+# you cause "cd" to echo its destination to stdout.  It can also take
+# scripts to unexpected places.  If you like CDPATH, define it for your
+# interactive shell sessions without exporting it.
+unexport CDPATH
+
 SCRIPT_SH += git-am.sh
 SCRIPT_SH += git-bisect.sh
 SCRIPT_SH += git-difftool--helper.sh
-- 
1.7.0