fix: mitigate collisions in field names

proto/message.py

@@ -524,6 +524,16 @@ def __init__(
         # coerced.
         marshal = self._meta.marshal
         for key, value in mapping.items():
+            # Underscores may be appended to field names
+            # that collide with python or proto-plus keywords.
+            # In case a key only exists with a `_` suffix, coerce the key
+            # to include the `_` suffix. Is not possible to
+            # natively define the same field with a trailing underscore in protobuf.
+            # See related issue
+            # https://github.com/googleapis/python-api-core/issues/227
+            if key not in self._meta.fields and f"{key}_" in self._meta.fields:
+                key = f"{key}_"
+
             try:
                 pb_type = self._meta.fields[key].pb_type
             except KeyError:

tests/test_fields_mitigate_collision.py

@@ -0,0 +1,41 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import proto
+
+
+# Underscores may be appended to field names
+# that collide with python or proto-plus keywords.
+# In case a key only exists with a `_` suffix, coerce the key
+# to include the `_` suffix. Is not possible to
+# natively define the same field with a trailing underscore in protobuf.
+# See related issue
+# https://github.com/googleapis/python-api-core/issues/227
+def test_fields_mitigate_collision():
+    class TestMessage(proto.Message):
+        spam_ = proto.Field(proto.STRING, number=1)
+        eggs = proto.Field(proto.STRING, number=2)
+
+    obj = TestMessage(spam_="has_spam")
+    obj.eggs = "has_eggs"
+    assert obj.spam_ == "has_spam"
+
+    modified_obj = TestMessage(
+        {
+           "spam": "has_spam",
+           "eggs": "has_eggs"
+        }
+    )
+
+    assert modified_obj.spam_ == "has_spam"