checkout/restore: add basic tests for --merge

Even though "checkout --merge -- paths" had some tests, we never
made sure it worked to recreate the conflicted state _after_ the
resolution was recorded in the index.  Also "restore --merge" did
not even have any tests.

Currently these commands use the unmerge_marked_index() interface
that cannot handle paths that have been resolved as removal, and
tests for that case are marked with test_expect_failure; these
should eventually be fixed, but not in this patch.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: gitster

t/t2070-restore.sh

@@ -137,6 +137,70 @@ test_expect_success 'restore --staged invalidates cache tree for deletions' '
 	test_must_fail git rev-parse HEAD:new1
 '
 
+test_expect_success 'restore --merge to unresolve' '
+	O=$(echo original | git hash-object -w --stdin) &&
+	A=$(echo ourside | git hash-object -w --stdin) &&
+	B=$(echo theirside | git hash-object -w --stdin) &&
+	{
+		echo "100644 $O 1	file" &&
+		echo "100644 $A 2	file" &&
+		echo "100644 $B 3	file"
+	} | git update-index --index-info &&
+	echo nothing >file &&
+	git restore --worktree --merge file &&
+	cat >expect <<-\EOF &&
+	<<<<<<< ours
+	ourside
+	=======
+	theirside
+	>>>>>>> theirs
+	EOF
+	test_cmp expect file
+'
+
+test_expect_success 'restore --merge to unresolve after (mistaken) resolution' '
+	O=$(echo original | git hash-object -w --stdin) &&
+	A=$(echo ourside | git hash-object -w --stdin) &&
+	B=$(echo theirside | git hash-object -w --stdin) &&
+	{
+		echo "100644 $O 1	file" &&
+		echo "100644 $A 2	file" &&
+		echo "100644 $B 3	file"
+	} | git update-index --index-info &&
+	echo nothing >file &&
+	git add file &&
+	git restore --worktree --merge file &&
+	cat >expect <<-\EOF &&
+	<<<<<<< ours
+	ourside
+	=======
+	theirside
+	>>>>>>> theirs
+	EOF
+	test_cmp expect file
+'
+
+test_expect_failure 'restore --merge to unresolve after (mistaken) resolution' '
+	O=$(echo original | git hash-object -w --stdin) &&
+	A=$(echo ourside | git hash-object -w --stdin) &&
+	B=$(echo theirside | git hash-object -w --stdin) &&
+	{
+		echo "100644 $O 1	file" &&
+		echo "100644 $A 2	file" &&
+		echo "100644 $B 3	file"
+	} | git update-index --index-info &&
+	git rm -f file &&
+	git restore --worktree --merge file &&
+	cat >expect <<-\EOF &&
+	<<<<<<< ours
+	ourside
+	=======
+	theirside
+	>>>>>>> theirs
+	EOF
+	test_cmp expect file
+'
+
 test_expect_success 'restore with merge options are incompatible with certain options' '
 	for opts in \
 		"--staged --ours" \

t/t7201-co.sh

@@ -522,6 +522,48 @@ test_expect_success 'checkout with --merge' '
 	test_cmp merged file
 '
 
+test_expect_success 'checkout -m works after (mistaken) resolution' '
+	setup_conflicting_index &&
+	echo "none of the above" >sample &&
+	cat sample >fild &&
+	cat sample >file &&
+	cat sample >filf &&
+	# resolve to something
+	git add file &&
+	git checkout --merge -- fild file filf &&
+	{
+		echo "<<<<<<< ours" &&
+		echo ourside &&
+		echo "=======" &&
+		echo theirside &&
+		echo ">>>>>>> theirs"
+	} >merged &&
+	test_cmp expect fild &&
+	test_cmp expect filf &&
+	test_cmp merged file
+'
+
+test_expect_failure 'checkout -m works after (mistaken) resolution to remove' '
+	setup_conflicting_index &&
+	echo "none of the above" >sample &&
+	cat sample >fild &&
+	cat sample >file &&
+	cat sample >filf &&
+	# resolve to remove
+	git rm file &&
+	git checkout --merge -- fild file filf &&
+	{
+		echo "<<<<<<< ours" &&
+		echo ourside &&
+		echo "=======" &&
+		echo theirside &&
+		echo ">>>>>>> theirs"
+	} >merged &&
+	test_cmp expect fild &&
+	test_cmp expect filf &&
+	test_cmp merged file
+'
+
 test_expect_success 'checkout with --merge, in diff3 -m style' '
 	git config merge.conflictstyle diff3 &&
 	setup_conflicting_index &&