1 files changed, 166 insertions, 0 deletions
diff --git a/t/t2020-checkout-detach.sh b/t/t2020-checkout-detach.sh
new file mode 100755
index 0000000000..5d68729d7a
--- /dev/null
+++ b/t/t2020-checkout-detach.sh
@@ -0,0 +1,166 @@
+#!/bin/sh
+
+test_description='checkout into detached HEAD state'
+. ./test-lib.sh
+
+check_detached () {
+	test_must_fail git symbolic-ref -q HEAD >/dev/null
+}
+
+check_not_detached () {
+	git symbolic-ref -q HEAD >/dev/null
+}
+
+PREV_HEAD_DESC='Previous HEAD position was'
+check_orphan_warning() {
+	test_i18ngrep "you are leaving $2 behind" "$1" &&
+	test_i18ngrep ! "$PREV_HEAD_DESC" "$1"
+}
+check_no_orphan_warning() {
+	test_i18ngrep ! "you are leaving .* commit.*behind" "$1" &&
+	test_i18ngrep "$PREV_HEAD_DESC" "$1"
+}
+
+reset () {
+	git checkout master &&
+	check_not_detached
+}
+
+test_expect_success 'setup' '
+	test_commit one &&
+	test_commit two &&
+	test_commit three && git tag -d three &&
+	test_commit four && git tag -d four &&
+	git branch branch &&
+	git tag tag
+'
+
+test_expect_success 'checkout branch does not detach' '
+	reset &&
+	git checkout branch &&
+	check_not_detached
+'
+
+test_expect_success 'checkout tag detaches' '
+	reset &&
+	git checkout tag &&
+	check_detached
+'
+
+test_expect_success 'checkout branch by full name detaches' '
+	reset &&
+	git checkout refs/heads/branch &&
+	check_detached
+'
+
+test_expect_success 'checkout non-ref detaches' '
+	reset &&
+	git checkout branch^ &&
+	check_detached
+'
+
+test_expect_success 'checkout ref^0 detaches' '
+	reset &&
+	git checkout branch^0 &&
+	check_detached
+'
+
+test_expect_success 'checkout --detach detaches' '
+	reset &&
+	git checkout --detach branch &&
+	check_detached
+'
+
+test_expect_success 'checkout --detach without branch name' '
+	reset &&
+	git checkout --detach &&
+	check_detached
+'
+
+test_expect_success 'checkout --detach errors out for non-commit' '
+	reset &&
+	test_must_fail git checkout --detach one^{tree} &&
+	check_not_detached
+'
+
+test_expect_success 'checkout --detach errors out for extra argument' '
+	reset &&
+	git checkout master &&
+	test_must_fail git checkout --detach tag one.t &&
+	check_not_detached
+'
+
+test_expect_success 'checkout --detached and -b are incompatible' '
+	reset &&
+	test_must_fail git checkout --detach -b newbranch tag &&
+	check_not_detached
+'
+
+test_expect_success 'checkout --detach moves HEAD' '
+	reset &&
+	git checkout one &&
+	git checkout --detach two &&
+	git diff --exit-code HEAD &&
+	git diff --exit-code two
+'
+
+test_expect_success 'checkout warns on orphan commits' '
+	reset &&
+	git checkout --detach two &&
+	echo content >orphan &&
+	git add orphan &&
+	git commit -a -m orphan1 &&
+	echo new content >orphan &&
+	git commit -a -m orphan2 &&
+	orphan2=$(git rev-parse HEAD) &&
+	git checkout master 2>stderr
+'
+
+test_expect_success 'checkout warns on orphan commits: output' '
+	check_orphan_warning stderr "2 commits"
+'
+
+test_expect_success 'checkout warns orphaning 1 of 2 commits' '
+	git checkout "$orphan2" &&
+	git checkout HEAD^ 2>stderr
+'
+
+test_expect_success 'checkout warns orphaning 1 of 2 commits: output' '
+	check_orphan_warning stderr "1 commit"
+'
+
+test_expect_success 'checkout does not warn leaving ref tip' '
+	reset &&
+	git checkout --detach two &&
+	git checkout master 2>stderr
+'
+
+test_expect_success 'checkout does not warn leaving ref tip' '
+	check_no_orphan_warning stderr
+'
+
+test_expect_success 'checkout does not warn leaving reachable commit' '
+	reset &&
+	git checkout --detach HEAD^ &&
+	git checkout master 2>stderr
+'
+
+test_expect_success 'checkout does not warn leaving reachable commit' '
+	check_no_orphan_warning stderr
+'
+
+cat >expect <<'EOF'
+Your branch is behind 'master' by 1 commit, and can be fast-forwarded.
+  (use "git pull" to update your local branch)
+EOF
+test_expect_success 'tracking count is accurate after orphan check' '
+	reset &&
+	git branch child master^ &&
+	git config branch.child.remote . &&
+	git config branch.child.merge refs/heads/master &&
+	git checkout child^ &&
+	git checkout child >stdout &&
+	test_i18ncmp expect stdout
+'
+
+test_done