Merge changes I64b553f2,Ied9fc2f7 into stable-3.6

* changes:
  Introduce general purpose Optional JSON serializer for GSON
  Add Optional type JSON (de)serialization unit tests

3 files changed, 198 insertions, 0 deletions

diff --git a/java/com/google/gerrit/json/OptionalTypeAdapter.java b/java/com/google/gerrit/json/OptionalTypeAdapter.java
new file mode 100644
index 0000000000..9bfa72dfde
--- /dev/null
+++ b/java/com/google/gerrit/json/OptionalTypeAdapter.java
@@ -0,0 +1,69 @@
+// Copyright (C) 2022 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.json;
+
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonNull;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import com.google.gson.JsonSerializationContext;
+import com.google.gson.JsonSerializer;
+import com.google.inject.TypeLiteral;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.Optional;
+
+public class OptionalTypeAdapter
+    implements JsonSerializer<Optional<?>>, JsonDeserializer<Optional<?>> {
+
+  private static final String VALUE = "value";
+
+  @Override
+  public JsonElement serialize(Optional<?> src, Type typeOfSrc, JsonSerializationContext context) {
+    Optional<?> optional = src == null ? Optional.empty() : src;
+    JsonObject json = new JsonObject();
+    json.add(VALUE, optional.map(context::serialize).orElse(JsonNull.INSTANCE));
+    return json;
+  }
+
+  @Override
+  public Optional<?> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
+      throws JsonParseException {
+    if (!json.getAsJsonObject().has(VALUE)) {
+      return Optional.empty();
+    }
+
+    JsonElement value = json.getAsJsonObject().get(VALUE);
+    if (value == null || value.isJsonNull()) {
+      return Optional.empty();
+    }
+
+    // handle the situation when one uses Optional without type parameter which is an equivalent of
+    // <?> type
+    ParameterizedType parameterizedType =
+        (ParameterizedType) new TypeLiteral<Optional<?>>() {}.getType();
+    if (typeOfT instanceof ParameterizedType) {
+      parameterizedType = (ParameterizedType) typeOfT;
+      if (parameterizedType.getActualTypeArguments().length != 1) {
+        throw new JsonParseException("Expected one parameter type in Optional.");
+      }
+    }
+
+    Type optionalOf = parameterizedType.getActualTypeArguments()[0];
+    return Optional.of(context.deserialize(value, optionalOf));
+  }
+}
diff --git a/java/com/google/gerrit/server/notedb/ChangeNoteJson.java b/java/com/google/gerrit/server/notedb/ChangeNoteJson.java
index 37a38fe403..0f1d362c76 100644
--- a/java/com/google/gerrit/server/notedb/ChangeNoteJson.java
+++ b/java/com/google/gerrit/server/notedb/ChangeNoteJson.java
@@ -18,6 +18,7 @@ import com.google.common.collect.ImmutableList;
 import com.google.gerrit.entities.EntitiesAdapterFactory;
 import com.google.gerrit.json.EnumTypeAdapterFactory;
 import com.google.gerrit.json.OptionalSubmitRequirementExpressionResultAdapterFactory;
+import com.google.gerrit.json.OptionalTypeAdapter;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonElement;
@@ -52,6 +53,7 @@ public class ChangeNoteJson {
 
   static Gson newGson() {
     return new GsonBuilder()
+        .registerTypeAdapter(Optional.class, new OptionalTypeAdapter())
         .registerTypeAdapter(Timestamp.class, new CommentTimestampAdapter().nullSafe())
         .registerTypeAdapterFactory(new EnumTypeAdapterFactory())
         .registerTypeAdapterFactory(EntitiesAdapterFactory.create())
diff --git a/javatests/com/google/gerrit/server/notedb/ChangeNoteJsonTest.java b/javatests/com/google/gerrit/server/notedb/ChangeNoteJsonTest.java
new file mode 100644
index 0000000000..24e28f376f
--- /dev/null
+++ b/javatests/com/google/gerrit/server/notedb/ChangeNoteJsonTest.java
@@ -0,0 +1,127 @@
+// Copyright (C) 2022 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.notedb;
+
+import static com.google.common.truth.Truth.assertThat;
+import static com.google.common.truth.Truth8.assertThat;
+
+import com.google.gson.Gson;
+import com.google.inject.TypeLiteral;
+import java.util.Optional;
+import org.junit.Test;
+
+public class ChangeNoteJsonTest {
+  private final Gson gson = new ChangeNoteJson().getGson();
+
+  static class Child {
+    Optional<String> optionalValue;
+  }
+
+  static class Parent {
+    Optional<Child> optionalChild;
+  }
+
+  @Test
+  public void shouldSerializeAndDeserializeEmptyOptional() {
+    // given
+    Optional<?> empty = Optional.empty();
+
+    // when
+    String json = gson.toJson(empty);
+
+    // then
+    assertThat(json).isEqualTo("{}");
+
+    // and when
+    Optional<?> result = gson.fromJson(json, Optional.class);
+
+    // and then
+    assertThat(result).isEmpty();
+  }
+
+  @Test
+  public void shouldSerializeAndDeserializeNonEmptyOptional() {
+    // given
+    String value = "foo";
+    Optional<String> nonEmpty = Optional.of(value);
+
+    // when
+    String json = gson.toJson(nonEmpty);
+
+    // then
+    assertThat(json).isEqualTo("{\n  \"value\": \"" + value + "\"\n}");
+
+    // and when
+    Optional<String> result = gson.fromJson(json, new TypeLiteral<Optional<String>>() {}.getType());
+
+    // and then
+    assertThat(result).isPresent();
+    assertThat(result.get()).isEqualTo(value);
+  }
+
+  @Test
+  public void shouldSerializeAndDeserializeNestedNonEmptyOptional() {
+    String value = "foo";
+    Child fooChild = new Child();
+    fooChild.optionalValue = Optional.of(value);
+    Parent parent = new Parent();
+    parent.optionalChild = Optional.of(fooChild);
+
+    String json = gson.toJson(parent);
+
+    assertThat(json)
+        .isEqualTo(
+            "{\n"
+                + "  \"optionalChild\": {\n"
+                + "    \"value\": {\n"
+                + "      \"optionalValue\": {\n"
+                + "        \"value\": \"foo\"\n"
+                + "      }\n"
+                + "    }\n"
+                + "  }\n"
+                + "}");
+
+    Parent result = gson.fromJson(json, new TypeLiteral<Parent>() {}.getType());
+
+    assertThat(result.optionalChild).isPresent();
+    assertThat(result.optionalChild.get().optionalValue).isPresent();
+    assertThat(result.optionalChild.get().optionalValue.get()).isEqualTo(value);
+  }
+
+  @Test
+  public void shouldSerializeAndDeserializeNestedEmptyOptional() {
+    Child fooChild = new Child();
+    fooChild.optionalValue = Optional.empty();
+    Parent parent = new Parent();
+    parent.optionalChild = Optional.of(fooChild);
+
+    String json = gson.toJson(parent);
+
+    assertThat(json)
+        .isEqualTo(
+            "{\n"
+                + "  \"optionalChild\": {\n"
+                + "    \"value\": {\n"
+                + "      \"optionalValue\": {}\n"
+                + "    }\n"
+                + "  }\n"
+                + "}");
+
+    Parent result = gson.fromJson(json, new TypeLiteral<Parent>() {}.getType());
+
+    assertThat(result.optionalChild).isPresent();
+    assertThat(result.optionalChild.get().optionalValue).isEmpty();
+  }
+}