Mark OneofDescriptor.isSynthetic() deprecated.

This API will be removed in a future breaking change.

PiperOrigin-RevId: 546004442

java/core/src/main/java/com/google/protobuf/Descriptors.java

@@ -2820,10 +2820,6 @@ public final class Descriptors {
       return proto.getOptions();
     }
 
-    public boolean isSynthetic() {
-      return fields.length == 1 && fields[0].isProto3Optional;
-    }
-
     /** Get a list of this message type's fields. */
     public List<FieldDescriptor> getFields() {
       return Collections.unmodifiableList(Arrays.asList(fields));
@@ -2838,6 +2834,12 @@ public final class Descriptors {
       return proto;
     }
 
+    @Deprecated
+    public
+    boolean isSynthetic() {
+      return fields.length == 1 && fields[0].isProto3Optional;
+    }
+
     private void setProto(final OneofDescriptorProto proto) {
       this.proto = proto;
     }

java/core/src/main/java/com/google/protobuf/LegacyDescriptorsUtil.java

@@ -31,6 +31,7 @@
 package com.google.protobuf;
 
 import com.google.protobuf.Descriptors.FileDescriptor;
+import com.google.protobuf.Descriptors.OneofDescriptor;
 
 /**
  * This file is meant to be a temporary housing for legacy descriptor APIs we want to deprecate and
@@ -69,5 +70,15 @@ public final class LegacyDescriptorsUtil {
     private LegacyFileDescriptor() {}
   }
 
+  /** Wraps OneofDescriptor */
+  public static final class LegacyOneofDescriptor {
+
+    public static boolean isSynthetic(OneofDescriptor descriptor) {
+      return descriptor.isSynthetic();
+    }
+
+    private LegacyOneofDescriptor() {}
+  }
+
   private LegacyDescriptorsUtil() {}
 }