1 files changed, 14 insertions, 5 deletions
diff --git a/src/google/protobuf/descriptor.cc b/src/google/protobuf/descriptor.cc
index 4dccb585..be1e1d69 100644
--- a/src/google/protobuf/descriptor.cc
+++ b/src/google/protobuf/descriptor.cc
@@ -4707,11 +4707,20 @@ void DescriptorBuilder::CheckEnumValueUniqueness(
     // stripping should de-dup the labels in this case).
     if (!inserted && insert_result.first->second->name() != value->name() &&
         insert_result.first->second->number() != value->number()) {
-      AddError(value->full_name(), proto.value(i),
-               DescriptorPool::ErrorCollector::NAME,
-               "When enum name is stripped and label is PascalCased (" +
-                   stripped + "), this value label conflicts with " +
-                   values[stripped]->name());
+      string error_message =
+          "When enum name is stripped and label is PascalCased (" + stripped +
+          "), this value label conflicts with " + values[stripped]->name() +
+          ". This will make the proto fail to compile for some languages, such "
+          "as C#.";
+      // There are proto2 enums out there with conflicting names, so to preserve
+      // compatibility we issue only a warning for proto2.
+      if (result->file()->syntax() == FileDescriptor::SYNTAX_PROTO2) {
+        AddWarning(value->full_name(), proto.value(i),
+                   DescriptorPool::ErrorCollector::NAME, error_message);
+      } else {
+        AddError(value->full_name(), proto.value(i),
+                 DescriptorPool::ErrorCollector::NAME, error_message);
+      }
     }
   }
 }