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

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

third_party/git/t/t0100-previous.sh

@@ -0,0 +1,68 @@
+#!/bin/sh
+
+test_description='previous branch syntax @{-n}'
+
+. ./test-lib.sh
+
+test_expect_success 'branch -d @{-1}' '
+	test_commit A &&
+	git checkout -b junk &&
+	git checkout - &&
+	test "$(git symbolic-ref HEAD)" = refs/heads/master &&
+	git branch -d @{-1} &&
+	test_must_fail git rev-parse --verify refs/heads/junk
+'
+
+test_expect_success 'branch -d @{-12} when there is not enough switches yet' '
+	git reflog expire --expire=now &&
+	git checkout -b junk2 &&
+	git checkout - &&
+	test "$(git symbolic-ref HEAD)" = refs/heads/master &&
+	test_must_fail git branch -d @{-12} &&
+	git rev-parse --verify refs/heads/master
+'
+
+test_expect_success 'merge @{-1}' '
+	git checkout A &&
+	test_commit B &&
+	git checkout A &&
+	test_commit C &&
+	test_commit D &&
+	git branch -f master B &&
+	git branch -f other &&
+	git checkout other &&
+	git checkout master &&
+	git merge @{-1} &&
+	git cat-file commit HEAD | grep "Merge branch '\''other'\''"
+'
+
+test_expect_success 'merge @{-1}~1' '
+	git checkout master &&
+	git reset --hard B &&
+	git checkout other &&
+	git checkout master &&
+	git merge @{-1}~1 &&
+	git cat-file commit HEAD >actual &&
+	grep "Merge branch '\''other'\''" actual
+'
+
+test_expect_success 'merge @{-100} before checking out that many branches yet' '
+	git reflog expire --expire=now &&
+	git checkout -f master &&
+	git reset --hard B &&
+	git branch -f other C &&
+	git checkout other &&
+	git checkout master &&
+	test_must_fail git merge @{-100}
+'
+
+test_expect_success 'log -g @{-1}' '
+	git checkout -b last_branch &&
+	git checkout -b new_branch &&
+	echo "last_branch@{0}" >expect &&
+	git log -g --format=%gd @{-1} >actual &&
+	test_cmp expect actual
+'
+
+test_done
+