Give FieldNamingStrategy the ability to return multiple String names (#2776)

* Give FieldNamingStrategy the ability to return multiple String names

* Fixed formatting violations

* Code review changes

- Changed fieldName to be added first to the fieldName list
- test which verifies that when 'alternate names' are configured they don't affect serialization, and only affect deserialization
- Updated translateToAlternateNames JavaDoc to refer it works like SerializedName#alternate()

* Removed usage of Stream.concat

Check Android compatibility test fails when using Stream.concat, switched to traditional Java method.

* Code Review Changes

1. Renamed badname to primary-name
2. Added test deserializing TranslateName with translateToAlternateNames

* Fixed typo

* added @since $next-version$ to translateToAlternateNames method

* Renamed translateToAlternateNames to alternateNames

* Merged the code with and without the SerializedName annotation

* Improved FieldNamingStrategy JavaDoc for the alternateNames method.

* Added special handling for annotation without alternate names

* Moved Collections.singletonList block to apply to both cases

* Update gson/src/main/java/com/google/gson/FieldNamingStrategy.java

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* Update gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* Update gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* Update gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* Update gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

---------

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

gson/src/main/java/com/google/gson/FieldNamingStrategy.java

@@ -16,7 +16,10 @@
 
 package com.google.gson;
 
+import com.google.gson.annotations.SerializedName;
 import java.lang.reflect.Field;
+import java.util.Collections;
+import java.util.List;
 
 /**
  * A mechanism for providing custom field naming in Gson. This allows the client code to translate
@@ -37,4 +40,16 @@ public interface FieldNamingStrategy {
    * @since 1.3
    */
   public String translateName(Field f);
+
+  /**
+   * Returns alternative names for this field when it is being deserialized. This is similar to
+   * {@link SerializedName#alternate()}.
+   *
+   * @param f the field object
+   * @return the list of alternative field names.
+   * @since $next-version$
+   */
+  default List<String> alternateNames(Field f) {
+    return Collections.emptyList();
+  }
 }

gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java

@@ -84,21 +84,25 @@ public final class ReflectiveTypeAdapterFactory implements TypeAdapterFactory {
   /** first element holds the default name */
   @SuppressWarnings("MixedMutabilityReturnType")
   private List<String> getFieldNames(Field f) {
+
+    String fieldName;
+    List<String> alternates;
     SerializedName annotation = f.getAnnotation(SerializedName.class);
     if (annotation == null) {
-      String name = fieldNamingPolicy.translateName(f);
-      return Collections.singletonList(name);
+      fieldName = fieldNamingPolicy.translateName(f);
+      alternates = fieldNamingPolicy.alternateNames(f);
+    } else {
+      fieldName = annotation.value();
+      alternates = Arrays.asList(annotation.alternate());
     }
 
-    String serializedName = annotation.value();
-    String[] alternates = annotation.alternate();
-    if (alternates.length == 0) {
-      return Collections.singletonList(serializedName);
+    if (alternates.isEmpty()) {
+      return Collections.singletonList(fieldName);
     }
 
-    List<String> fieldNames = new ArrayList<>(alternates.length + 1);
-    fieldNames.add(serializedName);
-    Collections.addAll(fieldNames, alternates);
+    List<String> fieldNames = new ArrayList<>(alternates.size() + 1);
+    fieldNames.add(fieldName);
+    fieldNames.addAll(alternates);
     return fieldNames;
   }
 

gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java

@@ -26,6 +26,7 @@ import com.google.gson.annotations.SerializedName;
 import com.google.gson.common.TestTypes.ClassWithSerializedNameFields;
 import com.google.gson.common.TestTypes.StringWrapper;
 import java.lang.reflect.Field;
+import java.util.List;
 import java.util.Locale;
 import org.junit.Before;
 import org.junit.Test;
@@ -237,6 +238,78 @@ public class NamingPolicyTest {
     assertThat(new Gson().toJson(new AtName())).isEqualTo("{\"@foo\":\"bar\"}");
   }
 
+  @Test
+  public void testGsonWithNameDeserialiation() {
+    Gson gson =
+        builder
+            .setFieldNamingStrategy(
+                new FieldNamingStrategy() {
+
+                  @Override
+                  public String translateName(Field f) {
+                    return "primary-name";
+                  }
+
+                  @Override
+                  public List<String> alternateNames(Field f) {
+                    return List.of("alternate-name");
+                  }
+                })
+            .create();
+    String target = "{\"primary-name\":\"someValue\"}";
+    StringWrapper deserializedObject = gson.fromJson(target, StringWrapper.class);
+    assertThat(deserializedObject.someConstantStringInstanceField).isEqualTo("someValue");
+  }
+
+  @Test
+  public void testGsonWithAlternateNamesDeserialiation() {
+    Gson gson =
+        builder
+            .setFieldNamingStrategy(
+                new FieldNamingStrategy() {
+
+                  @Override
+                  public String translateName(Field f) {
+                    return "primary-name";
+                  }
+
+                  @Override
+                  public List<String> alternateNames(Field f) {
+                    return List.of("alternate-name");
+                  }
+                })
+            .create();
+    String target = "{\"alternate-name\":\"someValue\"}";
+    StringWrapper deserializedObject = gson.fromJson(target, StringWrapper.class);
+    assertThat(deserializedObject.someConstantStringInstanceField).isEqualTo("someValue");
+  }
+
+  @Test
+  public void testGsonWithAlternateNamesSerialization() {
+    Gson gson =
+        builder
+            .setFieldNamingStrategy(
+                new FieldNamingStrategy() {
+
+                  @Override
+                  public String translateName(Field f) {
+                    return "some-constant-string-instance-field";
+                  }
+
+                  @Override
+                  public List<String> alternateNames(Field f) {
+                    return List.of("alternate-name");
+                  }
+                })
+            .create();
+    StringWrapper target = new StringWrapper("blah");
+    assertThat(gson.toJson(target))
+        .isEqualTo(
+            "{\"some-constant-string-instance-field\":\""
+                + target.someConstantStringInstanceField
+                + "\"}");
+  }
+
   static final class AtName {
     @SerializedName("@foo")
     String f = "bar";