fix(proto-plus): add context to TypeErrors during message manipulation

packages/proto-plus/proto/marshal/marshal.py

@@ -224,7 +224,8 @@ def to_proto(self, proto_type, value, *, strict: bool = False):
         # annotation. We need to do the conversion based on the `value`
         # field's type.
         if isinstance(value, dict) and (
-            proto_type.DESCRIPTOR.has_options
+            hasattr(proto_type, "DESCRIPTOR")
+            and proto_type.DESCRIPTOR.has_options
             and proto_type.DESCRIPTOR.GetOptions().map_entry
         ):
             recursive_type = type(proto_type().value)

packages/proto-plus/proto/message.py

@@ -659,28 +659,34 @@ def __init__(
                     mapping,
                 )
             )
-
         params = {}
         # Update the mapping to address any values that need to be
         # coerced.
         marshal = self._meta.marshal
-        for key, value in mapping.items():
-            (key, pb_type) = self._get_pb_type_from_key(key)
-            if pb_type is None:
-                if ignore_unknown_fields:
-                    continue
-
-                raise ValueError(
-                    "Unknown field for {}: {}".format(self.__class__.__name__, key)
-                )
+        try:
+            for key, value in mapping.items():
+                (key, pb_type) = self._get_pb_type_from_key(key)
+                if pb_type is None:
+                    if ignore_unknown_fields:
+                        continue
+
+                    raise ValueError(
+                        "Unknown field for {}: {}".format(self.__class__.__name__, key)
+                    )
 
-            pb_value = marshal.to_proto(pb_type, value)
+                pb_value = marshal.to_proto(pb_type, value)
 
-            if pb_value is not None:
-                params[key] = pb_value
+                if pb_value is not None:
+                    params[key] = pb_value
 
-        # Create the internal protocol buffer.
-        super().__setattr__("_pb", self._meta.pb(**params))
+            # Create the internal protocol buffer.
+            super().__setattr__("_pb", self._meta.pb(**params))
+        except TypeError as e:
+            raise TypeError(
+                "Failed to initialize {}. Underlying error: {}".format(
+                    self.__class__.__name__, e
+                )
+            ) from e
 
     def _get_pb_type_from_key(self, key):
         """Given a key, return the corresponding pb_type.
@@ -852,16 +858,23 @@ def __setattr__(self, key, value):
                 "Unknown field for {}: {}".format(self.__class__.__name__, key)
             )
 
-        pb_value = marshal.to_proto(pb_type, value)
+        try:
+            pb_value = marshal.to_proto(pb_type, value)
 
-        # Clear the existing field.
-        # This is the only way to successfully write nested falsy values,
-        # because otherwise MergeFrom will no-op on them.
-        self._pb.ClearField(key)
+            # Clear the existing field.
+            # This is the only way to successfully write nested falsy values,
+            # because otherwise MergeFrom will no-op on them.
+            self._pb.ClearField(key)
 
-        # Merge in the value being set.
-        if pb_value is not None:
-            self._pb.MergeFrom(self._meta.pb(**{key: pb_value}))
+            # Merge in the value being set.
+            if pb_value is not None:
+                self._pb.MergeFrom(self._meta.pb(**{key: pb_value}))
+        except TypeError as e:
+            raise TypeError(
+                "Failed to set field '{}' on {} to value {}. Underlying error: {}".format(
+                    key, self.__class__.__name__, value, e
+                )
+            ) from e
 
     def __getstate__(self):
         """Serialize for pickling."""

packages/proto-plus/tests/test_message.py

@@ -500,3 +500,39 @@ class Arm(proto.Message):
 
 def test_dir_message_base():
     assert set(dir(proto.Message)) == set(dir(type))
+
+
+def test_invalid_initialization_type_error():
+    """Verify that bad types passed to __init__ raise a descriptive TypeError."""
+
+    class UserProfile(proto.Message):
+        username = proto.Field(proto.STRING, number=1)
+        age = proto.Field(proto.INT32, number=2)
+
+    with pytest.raises(TypeError) as excinfo:
+        # Passing a list where a string is expected
+        UserProfile(username=["not", "a", "string"])
+
+    error_msg = str(excinfo.value)
+    assert "Failed to initialize UserProfile" in error_msg
+    assert "Underlying error" in error_msg
+    assert isinstance(excinfo.value.__cause__, TypeError)
+
+
+def test_invalid_assignment_type_error():
+    """Verify that bad types assigned via __setattr__ raise a descriptive TypeError."""
+
+    class UserProfile(proto.Message):
+        username = proto.Field(proto.STRING, number=1)
+        age = proto.Field(proto.INT32, number=2)
+
+    profile = UserProfile()
+
+    with pytest.raises(TypeError) as excinfo:
+        # Assigning a dictionary where an integer is expected
+        profile.age = {"invalid": "type"}
+
+    error_msg = str(excinfo.value)
+    assert "Failed to set field 'age' on UserProfile" in error_msg
+    assert "{'invalid': 'type'}" in error_msg
+    assert isinstance(excinfo.value.__cause__, TypeError)