Handle add with path="". Fixes #188

v5/patch.go

@@ -729,6 +729,32 @@ func (p Patch) add(doc *container, op Operation, options *ApplyOptions) error {
 		return errors.Wrapf(ErrMissing, "add operation failed to decode path")
 	}
 
+	// special case, adding to empty means replacing the container with the value given
+	if path == "" {
+		val := op.value()
+
+		var pd container
+		if (*val.raw)[0] == '[' {
+			pd = &partialArray{
+				self: val,
+			}
+		} else {
+			pd = &partialDoc{
+				self: val,
+			}
+		}
+
+		err := json.Unmarshal(*val.raw, pd)
+
+		if err != nil {
+			return err
+		}
+
+		*doc = pd
+
+		return nil
+	}
+
 	if options.EnsurePathExistsOnAdd {
 		err = ensurePathExists(doc, path, options)
 

v5/patch_test.go

@@ -592,6 +592,20 @@ var Cases = []Case{
 		false,
 		false,
 	},
+	{
+		`{}`,
+		`[{"op":"add","path":"","value":{"foo":"bar"}}]`,
+		`{"foo": "bar"}`,
+		false,
+		false,
+	},
+	{
+		`[]`,
+		`[{"op":"add","path":"","value":{"foo":"bar"}}, {"op": "add", "path": "/qux", "value": 1}]`,
+		`{"foo": "bar", "qux": 1}`,
+		false,
+		false,
+	},
 }
 
 type BadCase struct {