var: add GIT_DEFAULT_BRANCH variable

Introduce the logical variable GIT_DEFAULT_BRANCH which represents the
the default branch name that will be used by "git init".

Currently this variable is equivalent to
    git config init.defaultbranch || 'master'

This however will break if at one point the default branch is changed as
indicated by `default_branch_name_advice` in `refs.c`.

By providing this command ahead of time users of git can make their
code forward-compatible.

Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/t/t0007-git-var.sh b/t/t0007-git-var.sh
index 88b9ae8..3d6b71c 100755
--- a/t/t0007-git-var.sh
+++ b/t/t0007-git-var.sh
@@ -25,6 +25,26 @@ test_expect_success !FAIL_PREREQS,!AUTOIDENT 'requested identities are strict' '
 	)
 '
 
+test_expect_success 'get GIT_DEFAULT_BRANCH without configuration' '
+	(
+		sane_unset GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME &&
+		git init defbranch &&
+		git -C defbranch symbolic-ref --short HEAD >expect &&
+		git var GIT_DEFAULT_BRANCH >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'get GIT_DEFAULT_BRANCH with configuration' '
+	test_config init.defaultbranch foo &&
+	(
+		sane_unset GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME &&
+		echo foo >expect &&
+		git var GIT_DEFAULT_BRANCH >actual &&
+		test_cmp expect actual
+	)
+'
+
 # For git var -l, we check only a representative variable;
 # testing the whole output would make our test too brittle with
 # respect to unrelated changes in the test suite's environment.