From c311190cf88205e1537cad85b43aa4fc26c6e2f8 Mon Sep 17 00:00:00 2001
From: Adrien Vannson <adrien.vannson@protonmail.com>
Date: Thu, 31 Jul 2025 11:29:54 +0200
Subject: [PATCH] Fix unknown enum to dict

---
 betterproto2/src/betterproto2/__init__.py     |  5 +++++
 betterproto2/tests/test_all_definition.py     | 13 +++++++++++-
 betterproto2/tests/test_enum.py               | 10 +++++++++
 .../tests/inputs/enum/enum.proto              | 21 +++++++++++++++++++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/betterproto2/src/betterproto2/__init__.py b/betterproto2/src/betterproto2/__init__.py
index 24a02926..dc159eb5 100644
--- a/betterproto2/src/betterproto2/__init__.py
+++ b/betterproto2/src/betterproto2/__init__.py
@@ -588,6 +588,11 @@ def _value_to_dict(
         return b64encode(value).decode("utf8"), not bool(value)
     if proto_type == TYPE_ENUM:
         enum_value = field_type(value)
+
+        # If we don't know the definition of this variant, we fall back to the value.
+        if not enum_value.name:
+            return enum_value.value, not bool(value)
+
         return enum_value.proto_name or enum_value.name, not bool(value)
     if proto_type in (TYPE_FLOAT, TYPE_DOUBLE):
         return _dump_float(value), not bool(value)
diff --git a/betterproto2/tests/test_all_definition.py b/betterproto2/tests/test_all_definition.py
index eb2ec30d..ce22ae7c 100644
--- a/betterproto2/tests/test_all_definition.py
+++ b/betterproto2/tests/test_all_definition.py
@@ -17,4 +17,15 @@ def test_all_definition():
         "TestSyncStub",
         "ThingType",
     )
-    assert enum.__all__ == ("ArithmeticOperator", "Choice", "EnumMessage", "HttpCode", "NoStriping", "Test")
+    assert enum.__all__ == (
+        "ArithmeticOperator",
+        "Choice",
+        "EnumMessage",
+        "HttpCode",
+        "NewVersion",
+        "NewVersionMessage",
+        "NoStriping",
+        "OldVersion",
+        "OldVersionMessage",
+        "Test",
+    )
diff --git a/betterproto2/tests/test_enum.py b/betterproto2/tests/test_enum.py
index f8e0bc17..6dc12f78 100644
--- a/betterproto2/tests/test_enum.py
+++ b/betterproto2/tests/test_enum.py
@@ -98,3 +98,13 @@ def test_enum_to_dict() -> None:
         "arithmeticOperator": "ARITHMETIC_OPERATOR_PLUS",  # The original proto name must be preserved
         "noStriping": "NO_STRIPING_A",
     }
+
+
+def test_unknown_variant_to_dict() -> None:
+    from tests.outputs.enum.enum import NewVersion, NewVersionMessage, OldVersionMessage
+
+    serialized = bytes(NewVersionMessage(new_version=NewVersion.V3))
+
+    deserialized = OldVersionMessage.parse(serialized)
+
+    assert deserialized.to_dict() == {"oldVersion": 3}
diff --git a/betterproto2_compiler/tests/inputs/enum/enum.proto b/betterproto2_compiler/tests/inputs/enum/enum.proto
index fb2aa9fc..09e4499a 100644
--- a/betterproto2_compiler/tests/inputs/enum/enum.proto
+++ b/betterproto2_compiler/tests/inputs/enum/enum.proto
@@ -43,3 +43,24 @@ message EnumMessage {
     ArithmeticOperator arithmetic_operator = 1;
     NoStriping no_striping = 2;
 }
+
+enum OldVersion {
+    OLD_VERSION_UNSPECIFIED = 0;
+    OLD_VERSION_V1 = 1;
+    OLD_VERSION_V2 = 2;
+}
+
+message OldVersionMessage {
+    OldVersion old_version = 1;
+}
+
+enum NewVersion {
+    NEW_VERSION_UNSPECIFIED = 0;
+    NEW_VERSION_V1 = 1;
+    NEW_VERSION_V2 = 2;
+    NEW_VERSION_V3 = 3;
+}
+
+message NewVersionMessage {
+    NewVersion new_version = 1;
+}