merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/t2021-checkout-overwrite.sh

@@ -0,0 +1,54 @@
+#!/bin/sh
+
+test_description='checkout must not overwrite an untracked objects'
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+
+	mkdir -p a/b/c &&
+	>a/b/c/d &&
+	git add -A &&
+	git commit -m base &&
+	git tag start
+'
+
+test_expect_success 'create a commit where dir a/b changed to file' '
+
+	git checkout -b file &&
+	rm -rf a/b &&
+	>a/b &&
+	git add -A &&
+	git commit -m "dir to file"
+'
+
+test_expect_success 'checkout commit with dir must not remove untracked a/b' '
+
+	git rm --cached a/b &&
+	git commit -m "un-track the file" &&
+	test_must_fail git checkout start &&
+	test -f a/b
+'
+
+test_expect_success 'create a commit where dir a/b changed to symlink' '
+
+	rm -rf a/b &&	# cleanup if previous test failed
+	git checkout -f -b symlink start &&
+	rm -rf a/b &&
+	git add -A &&
+	test_ln_s_add foo a/b &&
+	git commit -m "dir to symlink"
+'
+
+test_expect_success 'checkout commit with dir must not remove untracked a/b' '
+
+	git rm --cached a/b &&
+	git commit -m "un-track the symlink" &&
+	test_must_fail git checkout start
+'
+
+test_expect_success SYMLINKS 'the symlink remained' '
+
+	test -h a/b
+'
+
+test_done