Add NumberedEnum interface (#4769)

Author: mrober

encoders/firebase-encoders-json/firebase-encoders-json.gradle

@@ -14,6 +14,7 @@
 
 plugins {
     id 'firebase-library'
+    id 'kotlin-android'
 }
 
 firebaseLibrary {
@@ -24,16 +25,19 @@ firebaseLibrary {
 android {
     compileSdkVersion project.targetSdkVersion
     defaultConfig {
-      minSdkVersion project.minSdkVersion
-      targetSdkVersion project.targetSdkVersion
-      versionName version
-      testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+        minSdkVersion project.minSdkVersion
+        targetSdkVersion project.targetSdkVersion
+        versionName version
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }
 
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_8
         targetCompatibility JavaVersion.VERSION_1_8
     }
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
     testOptions {
         unitTests {
             includeAndroidResources = true

encoders/firebase-encoders-json/src/main/java/com/google/firebase/encoders/json/JsonValueObjectEncoderContext.java

@@ -317,7 +317,11 @@ JsonValueObjectEncoderContext add(@Nullable Object o, boolean inline) throws IOE
 
     // Process enum last if it does not have a custom encoder registered.
     if (o instanceof Enum) {
-      add(((Enum) o).name());
+      if (o instanceof NumberedEnum) {
+        add(((NumberedEnum) o).getNumber());
+      } else {
+        add(((Enum<?>) o).name());
+      }
       return this;
     }
 

encoders/firebase-encoders-json/src/main/java/com/google/firebase/encoders/json/NumberedEnum.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * 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.firebase.encoders.json
+
+/** Represents an explicitly numbered enum for json serialization. */
+internal interface NumberedEnum {
+  val number: Int
+}

encoders/firebase-encoders-json/src/test/java/com/google/firebase/encoders/json/DummyEnum.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * 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.firebase.encoders.json
+
+internal enum class DummyEnum(override val number: Int) : NumberedEnum {
+  VALUE_1(1),
+  VALUE_2(2),
+}

encoders/firebase-encoders-json/src/test/java/com/google/firebase/encoders/json/JsonValueObjectEncoderContextTest.java

@@ -219,6 +219,18 @@ public void testEncodingEnum_withCustomEncoder() {
     assertThat(result).isEqualTo("[\"value_1\",\"value_2\"]");
   }
 
+  @Test
+  public void testEncodingNumberedEnum() {
+    String result =
+        new JsonDataEncoderBuilder()
+            .build()
+            .encode(
+                new DummyEnum[] {
+                  DummyEnum.VALUE_1, DummyEnum.VALUE_2, DummyEnum.VALUE_1, DummyEnum.VALUE_1
+                });
+    assertThat(result).isEqualTo("[1,2,1,1]");
+  }
+
   @Test
   public void testEncodingCollection() throws IOException {
     ObjectEncoder<InnerDummyClass> anotherObjectEncoder =