Fix from_dict unknown fields (#110)

Author: AdrienVannson

betterproto2/src/betterproto2/__init__.py

@@ -1108,16 +1108,23 @@ def to_dict(
         return output
 
     @classmethod
-    def _from_dict_init(cls, mapping: Mapping[str, Any] | Any) -> Mapping[str, Any]:
+    def _from_dict_init(cls, mapping: Mapping[str, Any] | Any, *, ignore_unknown_fields: bool) -> Mapping[str, Any]:
         init_kwargs: dict[str, Any] = {}
         for key, value in mapping.items():
             field_name = safe_snake_case(key)
-            field_cls = cls._betterproto.cls_by_field[field_name]
 
             try:
+                field_cls = cls._betterproto.cls_by_field[field_name]
                 meta = cls._betterproto.meta_by_field_name[field_name]
             except KeyError:
-                continue  # TODO is it a problem?
+                # According to the protobuf spec (https://protobuf.dev/programming-guides/json/): "The protobuf JSON
+                # parser should reject unknown fields by default but may provide an option to ignore unknown fields in
+                # parsing."
+                if ignore_unknown_fields:
+                    continue
+
+                raise KeyError(f"Unknown field '{field_name}' in message {cls.__name__}.") from None
+
             if value is None:
                 continue
 
@@ -1148,7 +1155,7 @@ def _from_dict_init(cls, mapping: Mapping[str, Any] | Any) -> Mapping[str, Any]:
         return init_kwargs
 
     @classmethod
-    def from_dict(cls: type[Self], value: Mapping[str, Any] | Any) -> Self:
+    def from_dict(cls: type[Self], value: Mapping[str, Any] | Any, *, ignore_unknown_fields: bool = False) -> Self:
         """
         Parse the key/value pairs into the a new message instance.
 
@@ -1165,7 +1172,7 @@ def from_dict(cls: type[Self], value: Mapping[str, Any] | Any) -> Self:
         if not isinstance(value, Mapping) and hasattr(cls, "from_wrapped"):  # type: ignore
             return cls.from_wrapped(value)  # type: ignore
 
-        return cls(**cls._from_dict_init(value))
+        return cls(**cls._from_dict_init(value, ignore_unknown_fields=ignore_unknown_fields))  # type: ignore
 
     def to_json(
         self,

betterproto2/tests/test_features.py

@@ -10,6 +10,8 @@
 )
 from unittest.mock import ANY
 
+import pytest
+
 import betterproto2
 from betterproto2 import OutputFormat
 
@@ -54,6 +56,15 @@ def test_unknown_fields():
     assert newer == new_again
 
 
+def test_from_dict_unknown_fields():
+    from tests.output_betterproto.features import Older
+
+    with pytest.raises(KeyError):
+        Older.from_dict({"x": True, "y": 1})
+
+    assert Older.from_dict({"x": True, "y": 1}, ignore_unknown_fields=True) == Older(x=True)
+
+
 def test_oneof_support():
     from tests.output_betterproto.features import IntMsg, OneofMsg