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

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

third_party/git/t/t7605-merge-resolve.sh

@@ -0,0 +1,52 @@
+#!/bin/sh
+
+test_description='git merge
+
+Testing the resolve strategy.'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	echo c0 > c0.c &&
+	git add c0.c &&
+	git commit -m c0 &&
+	git tag c0 &&
+	echo c1 > c1.c &&
+	git add c1.c &&
+	git commit -m c1 &&
+	git tag c1 &&
+	git reset --hard c0 &&
+	echo c2 > c2.c &&
+	git add c2.c &&
+	git commit -m c2 &&
+	git tag c2 &&
+	git reset --hard c0 &&
+	echo c3 > c2.c &&
+	git add c2.c &&
+	git commit -m c3 &&
+	git tag c3
+'
+
+merge_c1_to_c2_cmds='
+	git reset --hard c1 &&
+	git merge -s resolve c2 &&
+	test "$(git rev-parse c1)" != "$(git rev-parse HEAD)" &&
+	test "$(git rev-parse c1)" = "$(git rev-parse HEAD^1)" &&
+	test "$(git rev-parse c2)" = "$(git rev-parse HEAD^2)" &&
+	git diff --exit-code &&
+	test -f c0.c &&
+	test -f c1.c &&
+	test -f c2.c &&
+	test 3 = $(git ls-tree -r HEAD | wc -l) &&
+	test 3 = $(git ls-files | wc -l)
+'
+
+test_expect_success 'merge c1 to c2'        "$merge_c1_to_c2_cmds"
+
+test_expect_success 'merge c1 to c2, again' "$merge_c1_to_c2_cmds"
+
+test_expect_success 'merge c2 to c3 (fails)' '
+	git reset --hard c2 &&
+	test_must_fail git merge -s resolve c3
+'
+test_done