[PATCH v2 1/3] setup: Provide GIT_PREFIX to built-ins

[David Aguilar <davvid@gmail.com>]

GIT_PREFIX was added in 7cf16a14f5c070f7b14cf28023769450133172ae so that
aliases can know the directory from which a !alias was called.

Knowing the prefix relative to the root is helpful in other programs
so export it to built-ins as well.

Signed-off-by: David Aguilar <davvid@gmail.com>
---

The original version of this patch did not set GIT_PREFIX
to an empty string when prefix returns NULL.
Now we do.

 setup.c                 |    5 +++++
 t/t1020-subdirectory.sh |   16 ++++++++++++++++
 2 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/setup.c b/setup.c
index 013ad11..4569974 100644
--- a/setup.c
+++ b/setup.c
@@ -710,6 +710,11 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	const char *prefix;
 
 	prefix = setup_git_directory_gently_1(nongit_ok);
+	if (prefix)
+		setenv("GIT_PREFIX", prefix, 1);
+	else
+		setenv("GIT_PREFIX", "", 1);
+
 	if (startup_info) {
 		startup_info->have_repository = !nongit_ok || !*nongit_ok;
 		startup_info->prefix = prefix;
diff --git a/t/t1020-subdirectory.sh b/t/t1020-subdirectory.sh
index ddc3921..3c74480 100755
--- a/t/t1020-subdirectory.sh
+++ b/t/t1020-subdirectory.sh
@@ -139,6 +139,22 @@ test_expect_success 'GIT_PREFIX for !alias' '
 	test_cmp expect actual
 '
 
+test_expect_success 'GIT_PREFIX for built-ins' '
+	# Use GIT_EXTERNAL_DIFF to test that the "diff" built-in
+	# receives the GIT_PREFIX variable.
+	printf "dir/" >expect &&
+	printf "#!/bin/sh\n" >diff &&
+	printf "printf \"\$GIT_PREFIX\"" >>diff &&
+	chmod +x diff &&
+	(
+		cd dir &&
+		printf "change" >two &&
+		env GIT_EXTERNAL_DIFF=./diff git diff >../actual
+		git checkout -- two
+	) &&
+	test_cmp expect actual
+'
+
 test_expect_success 'no file/rev ambiguity check inside .git' '
 	git commit -a -m 1 &&
 	(
-- 
1.7.5.2.660.g9f46