parser: ensure prefix is separated when traversing

src/betterproto/plugin/parser.py

@@ -44,12 +44,12 @@ def _traverse(
         for i, item in enumerate(items):
             # Adjust the name since we flatten the hierarchy.
             # Todo: don't change the name, but include full name in returned tuple
-            item.name = next_prefix = prefix + item.name
+            item.name = next_prefix = f"{prefix}_{item.name}"
             yield item, path + [i]
 
             if isinstance(item, DescriptorProto):
                 for enum in item.enum_type:
-                    enum.name = next_prefix + enum.name
+                    enum.name = f"{next_prefix}_{enum.name}"
                     yield enum, path + [i, 4]
 
                 if item.nested_type:

tests/inputs/casing_inner_class/casing_inner_class.proto

@@ -0,0 +1,11 @@
+// https://github.com/danielgtaylor/python-betterproto/issues/344
+syntax = "proto3";
+
+package casing_inner_class;
+
+message Test {
+  message inner_class {
+    sint32 old_exp = 1;
+  }
+  inner_class inner = 2;
+}

tests/inputs/casing_inner_class/test_casing_inner_class.py

@@ -0,0 +1,14 @@
+import tests.output_betterproto.casing_inner_class as casing_inner_class
+
+
+def test_message_casing_inner_class_name():
+    assert hasattr(
+        casing_inner_class, "TestInnerClass"
+    ), "Inline defined Message is correctly converted to CamelCase"
+
+
+def test_message_casing_inner_class_attributes():
+    message = casing_inner_class.Test()
+    assert hasattr(
+        message.inner, "old_exp"
+    ), "Inline defined Message attribute is snake_case"