fix: avoid Pydantic namespace shadowing in Message.parse

betterproto2/src/betterproto2/__init__.py

@@ -1019,7 +1019,13 @@ def parse(cls, data: bytes) -> Self:
         :class:`Message`
             The initialized message.
         """
+        # Do not leave the parameter named ``data`` in the local frame while
+        # constructing a Pydantic dataclass.  Generated modules commonly use
+        # a module-level ``data`` alias for nested enums; Pydantic's lazy
+        # forward-reference resolver can otherwise see this bytes argument
+        # and resolve ``data.SomeEnum`` against ``bytes``.
         with BytesIO(data) as stream:
+            del data
             return cls().load(stream)
 
     # For compatibility with other libraries.

betterproto2/tests/test_pydantic_forward_refs.py

@@ -0,0 +1,32 @@
+from enum import IntEnum
+from types import SimpleNamespace
+
+from pydantic.dataclasses import dataclass
+
+import betterproto2
+
+
+@dataclass(eq=False, repr=False)
+class GeneratedMessage(betterproto2.Message):
+    # This mirrors python-betterproto2 output where a direct child package is
+    # imported as ``data`` after the class declarations.
+    namespace: "data.GeneratedNamespace" = betterproto2.field(
+        1,
+        betterproto2.TYPE_ENUM,
+        default_factory=lambda: data.GeneratedNamespace(0),
+    )
+
+
+class GeneratedNamespace(IntEnum):
+    UNKNOWN = 0
+
+
+data = SimpleNamespace(GeneratedNamespace=GeneratedNamespace)
+
+
+def test_pydantic_forward_reference_resolves_on_cold_parse():
+    assert GeneratedMessage.parse(b"").namespace is GeneratedNamespace.UNKNOWN
+
+
+def test_pydantic_forward_reference_resolves_for_keyword_data_argument():
+    assert GeneratedMessage.parse(data=b"").namespace is GeneratedNamespace.UNKNOWN