Add merge patch functionality from RFC7386

Summary: Merge patch is simple method of editing JSON documents. This implementation uses the recursive version documented in the RFC.

Reviewed By: yfeldblum

Differential Revision: D6777104

fbshipit-source-id: 554f801fe793a6fe004a8321ca41510b48225aa9

folly/dynamic-inl.h

@@ -641,6 +641,29 @@ inline void dynamic::update_missing(const dynamic& mergeObj1) {
   }
 }
 
+inline void dynamic::merge_patch(const dynamic& patch) {
+  auto& self = *this;
+  if (!patch.isObject()) {
+    self = patch;
+    return;
+  }
+  // if we are not an object, erase all contents, reset to object
+  if (!isObject()) {
+    self = object;
+  }
+  for (const auto& pair : patch.items()) {
+    if (pair.second.isNull()) {
+      // if name could be found in current object, remove it
+      auto it = self.find(pair.first);
+      if (it != self.items().end()) {
+        self.erase(it);
+      }
+    } else {
+      self[pair.first].merge_patch(pair.second);
+    }
+  }
+}
+
 inline dynamic dynamic::merge(
     const dynamic& mergeObj1,
     const dynamic& mergeObj2) {

folly/dynamic.h

@@ -465,6 +465,12 @@ struct dynamic : private boost::operators<dynamic> {
   void update_missing(const dynamic& other);
   static dynamic merge(const dynamic& mergeObj1, const dynamic& mergeObj2);
 
+  /*
+   * Implement recursive version of RFC7386: JSON merge patch. This modifies
+   * the current object.
+   */
+  void merge_patch(const dynamic& patch);
+
   /*
    * Erase an element from a dynamic object, by key.
    *

folly/test/DynamicTest.cpp

@@ -623,3 +623,98 @@ TEST(Dynamic, ObjectIteratorInterop) {
   decltype(cit) cit2 = it2;
   EXPECT_EQ(cit, cit2);
 }
+
+TEST(Dynamic, MergePatchWithNonObject) {
+  dynamic target = dynamic::object("a", "b")("c", "d");
+
+  dynamic patch = dynamic::array(1, 2, 3);
+  target.merge_patch(patch);
+
+  EXPECT_TRUE(target.isArray());
+}
+
+TEST(Dynamic, MergePatchReplaceInFlatObject) {
+  dynamic target = dynamic::object("a", "b")("c", "d");
+  dynamic patch = dynamic::object("a", "z");
+
+  target.merge_patch(patch);
+
+  EXPECT_EQ("z", target["a"].getString());
+  EXPECT_EQ("d", target["c"].getString());
+}
+
+TEST(Dynamic, MergePatchAddInFlatObject) {
+  dynamic target = dynamic::object("a", "b")("c", "d");
+  dynamic patch = dynamic::object("e", "f");
+  target.merge_patch(patch);
+
+  EXPECT_EQ("b", target["a"].getString());
+  EXPECT_EQ("d", target["c"].getString());
+  EXPECT_EQ("f", target["e"].getString());
+}
+
+TEST(Dynamic, MergePatchReplaceInNestedObject) {
+  dynamic target = dynamic::object("a", dynamic::object("d", 10))("b", "c");
+  dynamic patch = dynamic::object("a", dynamic::object("d", 100));
+  target.merge_patch(patch);
+
+  EXPECT_EQ(100, target["a"]["d"].getInt());
+  EXPECT_EQ("c", target["b"].getString());
+}
+
+TEST(Dynamic, MergePatchAddInNestedObject) {
+  dynamic target = dynamic::object("a", dynamic::object("d", 10))("b", "c");
+  dynamic patch = dynamic::object("a", dynamic::object("e", "f"));
+
+  target.merge_patch(patch);
+
+  EXPECT_EQ(10, target["a"]["d"].getInt());
+  EXPECT_EQ("f", target["a"]["e"].getString());
+  EXPECT_EQ("c", target["b"].getString());
+}
+
+TEST(Dynamic, MergeNestePatch) {
+  dynamic target = dynamic::object("a", dynamic::object("d", 10))("b", "c");
+  dynamic patch = dynamic::object(
+      "a", dynamic::object("d", dynamic::array(1, 2, 3)))("b", 100);
+  target.merge_patch(patch);
+
+  EXPECT_EQ(100, target["b"].getInt());
+  {
+    auto ary = patch["a"]["d"];
+    ASSERT_TRUE(ary.isArray());
+    EXPECT_EQ(1, ary[0].getInt());
+    EXPECT_EQ(2, ary[1].getInt());
+    EXPECT_EQ(3, ary[2].getInt());
+  }
+}
+
+TEST(Dynamic, MergePatchRemoveInFlatObject) {
+  dynamic target = dynamic::object("a", "b")("c", "d");
+  dynamic patch = dynamic::object("c", nullptr);
+  target.merge_patch(patch);
+
+  EXPECT_EQ("b", target["a"].getString());
+  EXPECT_EQ(0, target.count("c"));
+}
+
+TEST(Dynamic, MergePatchRemoveInNestedObject) {
+  dynamic target =
+      dynamic::object("a", dynamic::object("d", 10)("e", "f"))("b", "c");
+  dynamic patch = dynamic::object("a", dynamic::object("e", nullptr));
+  target.merge_patch(patch);
+
+  EXPECT_EQ(10, target["a"]["d"].getInt());
+  EXPECT_EQ(0, target["a"].count("e"));
+  EXPECT_EQ("c", target["b"].getString());
+}
+
+TEST(Dynamic, MergePatchRemoveNonExistent) {
+  dynamic target = dynamic::object("a", "b")("c", "d");
+  dynamic patch = dynamic::object("e", nullptr);
+  target.merge_patch(patch);
+
+  EXPECT_EQ("b", target["a"].getString());
+  EXPECT_EQ("d", target["c"].getString());
+  EXPECT_EQ(2, target.size());
+}