[PATCH v2 1/9] config: allow customizing /etc/gitconfig location with an environment

[Junio C Hamano <gitster@pobox.com>]

We introduced GIT_CONFIG_NOSYSTEM environment variable at ab88c363
("allow suppressing of global and system config", 2008-02-06),
primarily to protect our tests from random set of configuration
variables the system administrators would put in /etc/gitconfig
file.

Introduce a new environment variable GIT_CONFIG_SYSTEM_PATH, and allow
the users to specify a file that is used instead of /etc/gitconfig
to read (and write) the system-wide configuration.  By doing so, we
can force our tests to honor certain configuration settings by
default by pointing GIT_CONFIG_SYSTEM_PATH at our own, in addition to the
existing GIT_CONFIG_NOSYSTEM mechanism.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 cache.h                |  1 +
 config.c               |  2 ++
 t/gitconfig-for-test   |  6 ++++++
 t/t1300-repo-config.sh | 15 +++++++++++++++
 t/test-lib.sh          |  4 ++--
 5 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 t/gitconfig-for-test

diff --git a/cache.h b/cache.h
index b0dae4bac1a1..d4b689f386d6 100644
--- a/cache.h
+++ b/cache.h
@@ -408,6 +408,7 @@ static inline enum object_type object_type(unsigned int mode)
 #define GIT_NAMESPACE_ENVIRONMENT "GIT_NAMESPACE"
 #define GIT_WORK_TREE_ENVIRONMENT "GIT_WORK_TREE"
 #define GIT_PREFIX_ENVIRONMENT "GIT_PREFIX"
+#define GIT_CONFIG_SYSTEM_PATH_ENVIRONMENT "GIT_CONFIG_SYSTEM_PATH"
 #define DEFAULT_GIT_DIR_ENVIRONMENT ".git"
 #define DB_ENVIRONMENT "GIT_OBJECT_DIRECTORY"
 #define INDEX_ENVIRONMENT "GIT_INDEX_FILE"
diff --git a/config.c b/config.c
index 0dfed682b868..096bb754aad7 100644
--- a/config.c
+++ b/config.c
@@ -1253,6 +1253,8 @@ const char *git_etc_gitconfig(void)
 {
 	static const char *system_wide;
 	if (!system_wide)
+		system_wide = getenv(GIT_CONFIG_SYSTEM_PATH_ENVIRONMENT);
+	if (!system_wide)
 		system_wide = system_path(ETC_GITCONFIG);
 	return system_wide;
 }
diff --git a/t/gitconfig-for-test b/t/gitconfig-for-test
new file mode 100644
index 000000000000..4598885ed5c3
--- /dev/null
+++ b/t/gitconfig-for-test
@@ -0,0 +1,6 @@
+;; This file is used as if it were /etc/gitconfig while running the
+;; test scripts in this directory.
+;;
+;; [user]
+;;	name = A U Thor
+;;	email = author@example.com
diff --git a/t/t1300-repo-config.sh b/t/t1300-repo-config.sh
index 923bfc5a2606..0543b62227bf 100755
--- a/t/t1300-repo-config.sh
+++ b/t/t1300-repo-config.sh
@@ -1372,4 +1372,19 @@ test_expect_success !MINGW '--show-origin blob ref' '
 	test_cmp expect output
 '
 
+test_expect_success 'system-wide configuration' '
+	system="$TRASH_DIRECTORY/system-wide" &&
+	>"$system" &&
+	git config -f "$system" --add frotz.nitfol xyzzy &&
+
+	git config -f "$system" frotz.nitfol >expect &&
+	GIT_CONFIG_SYSTEM_PATH="$system" \
+	git config --system frotz.nitfol >actual &&
+
+	GIT_CONFIG_SYSTEM_PATH="$system" \
+	git config --system --replace-all frotz.nitfol blorb &&
+	echo blorb >expect &&
+	GIT_CONFIG_SYSTEM_PATH="$system" git config --system frotz.nitfol >actual
+'
+
 test_done
diff --git a/t/test-lib.sh b/t/test-lib.sh
index ac56512a1c5e..b811e4c70273 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -851,9 +851,9 @@ else # normal case, use ../bin-wrappers only unless $with_dashes:
 	fi
 fi
 GIT_TEMPLATE_DIR="$GIT_BUILD_DIR"/templates/blt
-GIT_CONFIG_NOSYSTEM=1
+GIT_CONFIG_SYSTEM_PATH="$GIT_BUILD_DIR/t/gitconfig-for-test"
 GIT_ATTR_NOSYSTEM=1
-export PATH GIT_EXEC_PATH GIT_TEMPLATE_DIR GIT_CONFIG_NOSYSTEM GIT_ATTR_NOSYSTEM
+export PATH GIT_EXEC_PATH GIT_TEMPLATE_DIR GIT_CONFIG_SYSTEM_PATH GIT_ATTR_NOSYSTEM
 
 if test -z "$GIT_TEST_CMP"
 then
-- 
2.10.0-589-g5adf4e1