Function ensurePathExists should handle appending correctly

v5/patch.go

@@ -766,9 +766,9 @@ func ensurePathExists(pd *container, path string, options *ApplyOptions) error {
 				}
 			}
 
-			// Check if the next part is a numeric index.
+			// Check if the next part is a numeric index or "-".
 			// If yes, then create an array, otherwise, create an object.
-			if arrIndex, err = strconv.Atoi(parts[pi+1]); err == nil {
+			if arrIndex, err = strconv.Atoi(parts[pi+1]); err == nil || parts[pi+1] == "-" {
 				if arrIndex < 0 {
 
 					if !options.SupportNegativeIndices {

v5/patch_test.go

@@ -215,6 +215,34 @@ var Cases = []Case{
 		false,
 		false,
 	},
+	{
+		`{ "foo": [{"bar": [{"baz0": "123"}]}]}`,
+		`[ { "op": "add", "path": "/foo/0/bar/-", "value": {"baz1": "456"} } ]`,
+		`{ "foo": [{"bar": [{"baz0": "123"}, {"baz1": "456"}]}]}`,
+		true,
+		true,
+	},
+	{
+		`{ "foo": [{"bar": [{"baz0": "123"}]}]}`,
+		`[ { "op": "add", "path": "/foo/1/bar/0", "value": {"baz1": "456"} } ]`,
+		`{ "foo": [{"bar": [{"baz0": "123"}]}, {"bar": [{"baz1": "456"}]}]}`,
+		true,
+		true,
+	},
+	{
+		`{ "foo": [{"bar": [{"baz0": "123"}]}]}`,
+		`[ { "op": "add", "path": "/foo/1/bar/-1", "value": {"baz1": "456"} } ]`,
+		`{ "foo": [{"bar": [{"baz0": "123"}]}, {"bar": [{"baz1": "456"}]}]}`,
+		true,
+		true,
+	},
+	{
+		`{ "foo": [{"bar": [{"baz0": "123"}]}]}`,
+		`[ { "op": "add", "path": "/foo/1/bar/-", "value": {"baz1": "456"} } ]`,
+		`{ "foo": [{"bar": [{"baz0": "123"}]}, {"bar": [{"baz1": "456"}]}]}`,
+		true,
+		true,
+	},
 	{
 		`{ "foo": "bar", "qux": { "baz": 1, "bar": null } }`,
 		`[ { "op": "remove", "path": "/qux/bar" } ]`,