[PATCHv2] Fix backwards-incompatible handling of core.sharedRepository

[Petr Baudis <pasky@suse.cz>]

The 06cbe8550324e0fd2290839bf3b9a92aa53b70ab core.sharedRepository
handling extension broke backwards compatibility; before, shared=1 meant
that Git merely ensured the repository is group-writable, not that it's
_only_ group-writable, which is the current behaviour. Thus, with umask 002,
Git creates repository with /rw.rw.--./, this patch fixes it back to
/rw.rw.r-./.

Maybe it makes sense to provide the current semantics in some way too,
but that cannot be done at the expense of ditching backwards
compatibility; this bug has just wasted me two hours and broke
repo.or.cz pushing for several hours.

Cc: Heikki Orsila <heikki.orsila@iki.fi>
Signed-off-by: Petr Baudis <pasky@rover.dkm.cz>
---

  The patch description is clarified and a test is added to t1301.

 path.c                 |    2 +-
 t/t1301-shared-repo.sh |   19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletions(-)


diff --git a/path.c b/path.c
index 5983255..75c5915 100644
--- a/path.c
+++ b/path.c
@@ -269,7 +269,7 @@ int adjust_shared_perm(const char *path)
 	mode = st.st_mode;
 
 	if (shared_repository) {
-		int tweak = shared_repository;
+		int tweak = (mode & 0777) | shared_repository;
 		if (!(mode & S_IWUSR))
 			tweak &= ~0222;
 		mode = (mode & ~0777) | tweak;
diff --git a/t/t1301-shared-repo.sh b/t/t1301-shared-repo.sh
index 6c78c8b..d26191b 100755
--- a/t/t1301-shared-repo.sh
+++ b/t/t1301-shared-repo.sh
@@ -17,6 +17,25 @@ test_expect_success 'shared = 0400 (faulty permission u-w)' '
 	test $ret != "0"
 '
 
+test_expect_success 'shared=1 does not override sane umask' '
+	mkdir sub &&
+	cd sub &&
+	umask 002 &&
+	git init --shared=1 &&
+	test 1 = $(git config core.sharedrepository) &&
+	actual="$(ls -l .git/HEAD)" &&
+	rm -rf sub &&
+	case "$actual" in
+	-rw-rw-r--*)
+		: happy
+		;;
+	*)
+		echo Oops, .git/HEAD is not 0664 but $actual
+		false
+		;;
+	esac
+'
+
 test_expect_success 'shared=all' '
 	mkdir sub &&
 	cd sub &&