🐛 Support Python 3.10+ union syntax (T | None), fixes #193

Author: drzbida

docs/annotating_fields.md

@@ -84,6 +84,8 @@ assert bytes(Message(foo=[1, 2])) == b"\x08\x01\x08\x02"
 
 Required fields are [deprecated](https://developers.google.com/protocol-buffers/docs/style#things_to_avoid) in `proto2` and not supported in `proto3`, thus in `pure-protobuf` fields are always optional. `#!python Optional` annotation is accepted for type hinting, but has no functional meaning for `#!python BaseMessage`.
 
+Both traditional `#!python Optional[T]` and modern Python 3.10+ union syntax `#!python T | None` are supported and work identically.
+
 ## Default values
 
 In `pure-protobuf` it's developer's responsibility to take care of default values. If encoded message does not contain a particular element, the corresponding field stays unprovided:

pure_protobuf/helpers/_typing.py

@@ -8,6 +8,13 @@
 except ImportError:
     NoneType = type(None)  # type: ignore
 
+try:
+    from types import UnionType  # type: ignore
+
+    UNION_TYPES = (Union, UnionType)
+except ImportError:
+    UNION_TYPES = (Union,)  # type: ignore
+
 
 class Sentinel:  # pragma: no cover
     """Sentinel object used for defaults."""
@@ -32,7 +39,7 @@ def extract_repeated(hint: Any) -> tuple[Any, TypeGuard[list]]:
 
 def extract_optional(hint: Any) -> tuple[Any, bool]:
     """Extract a possible optional flag."""
-    if get_origin(hint) is Union:
+    if get_origin(hint) in UNION_TYPES:
         cleaned_args = tuple(arg for arg in get_args(hint) if arg is not NoneType)
         return Union[cleaned_args], True
     return hint, False

tests/helpers/test_typing.py

@@ -1,3 +1,4 @@
+import sys
 from collections.abc import Iterable
 from typing import Any, Optional, Union
 
@@ -28,3 +29,9 @@ def test_extract_optional(hint: Any, expected_flag: bool, expected_inner: Any) -
 )
 def test_extract_repeated(hint: Any, expected_flag: bool, expected_inner: Any) -> None:
     assert extract_repeated(hint) == (expected_inner, expected_flag)
+
+
+@mark.skipif(sys.version_info < (3, 10), reason="Union syntax requires Python 3.10+")
+def test_extract_optional_union_syntax() -> None:
+    assert extract_optional(int | None) == (int, True)  # type: ignore
+    assert extract_optional(str | None) == (str, True)  # type: ignore