Merge branch 'nd/checkout-f-while-conflicted-fix'

"git checkout -f <branch>" while the index has an unmerged path
incorrectly left some paths in an unmerged state, which has been
corrected.

* nd/checkout-f-while-conflicted-fix:
  unpack-trees: fix oneway_merge accidentally carry over stage index

t/t2023-checkout-m.sh

@@ -46,4 +46,28 @@ test_expect_success '-m restores 3-way conflicted+resolved file' '
 	test_cmp both.txt.conflicted.cleaned both.txt.cleaned
 '
 
+test_expect_success 'force checkout a conflict file creates stage zero entry' '
+	git init co-force &&
+	(
+		cd co-force &&
+		echo a >a &&
+		git add a &&
+		git commit -ama &&
+		A_OBJ=$(git rev-parse :a) &&
+		git branch topic &&
+		echo b >a &&
+		git commit -amb &&
+		B_OBJ=$(git rev-parse :a) &&
+		git checkout topic &&
+		echo c >a &&
+		C_OBJ=$(git hash-object a) &&
+		git checkout -m master &&
+		test_cmp_rev :1:a $A_OBJ &&
+		test_cmp_rev :2:a $B_OBJ &&
+		test_cmp_rev :3:a $C_OBJ &&
+		git checkout -f topic &&
+		test_cmp_rev :0:a $A_OBJ
+	)
+'
+
 test_done

unpack-trees.c

@@ -2386,7 +2386,7 @@ int oneway_merge(const struct cache_entry * const *src,
 		if (o->update && S_ISGITLINK(old->ce_mode) &&
 		    should_update_submodules() && !verify_uptodate(old, o))
 			update |= CE_UPDATE;
-		add_entry(o, old, update, 0);
+		add_entry(o, old, update, CE_STAGEMASK);
 		return 0;
 	}
 	return merged_entry(a, old, o);