Replace extra decorator with property and lazy initialization so that it is backward compatible.

betterproto/__init__.py

@@ -433,9 +433,9 @@ T = TypeVar("T", bound="Message")
 
 
 class ProtoClassMetadata:
-    cls: "Message"
+    cls: Type["Message"]
 
-    def __init__(self, cls: "Message"):
+    def __init__(self, cls: Type["Message"]):
         self.cls = cls
         by_field = {}
         by_group = {}
@@ -452,6 +452,9 @@ class ProtoClassMetadata:
         self.oneof_group_by_field = by_field
         self.oneof_field_by_group = by_group
 
+        self.init_default_gen()
+        self.init_cls_by_field()
+
     def init_default_gen(self):
         default_gen = {}
 
@@ -478,7 +481,6 @@ class ProtoClassMetadata:
                     ],
                     bases=(Message,),
                 )
-                make_protoclass(Entry)
                 field_cls[field.name] = Entry
                 field_cls[field.name + ".value"] = vt
             else:
@@ -486,26 +488,6 @@ class ProtoClassMetadata:
 
         self.cls_by_field = field_cls
 
-    def __getattr__(self, item):
-        # Lazy init because forward reference classes may not be available at the beginning.
-        if item == 'default_gen':
-            self.init_default_gen()
-            return self.default_gen
-
-        if item == 'cls_by_field':
-            self.init_cls_by_field()
-            return self.cls_by_field
-
-
-def make_protoclass(cls):
-    setattr(cls, "_betterproto", ProtoClassMetadata(cls))
-
-
-def protoclass(*args, **kwargs):
-    cls = dataclasses.dataclass(*args, **kwargs)
-    make_protoclass(cls)
-    return cls
-
 
 class Message(ABC):
     """
@@ -567,6 +549,19 @@ class Message(ABC):
 
         super().__setattr__(attr, value)
 
+    @property
+    def _betterproto(self):
+        """
+        Lazy initialize metadata for each protobuf class.
+        It may be initialized multiple times in a multi-threaded environment,
+        but that won't affect the correctness.
+        """
+        meta = getattr(self.__class__, "_betterproto_meta", None)
+        if not meta:
+            meta = ProtoClassMetadata(self.__class__)
+            self.__class__._betterproto_meta = meta
+        return meta
+
     def __bytes__(self) -> bytes:
         """
         Get the binary encoded Protobuf representation of this instance.
@@ -932,7 +927,7 @@ def which_one_of(message: Message, group_name: str) -> Tuple[str, Any]:
     return (field.name, getattr(message, field.name))
 
 
-@protoclass
+@dataclasses.dataclass
 class _Duration(Message):
     # Signed seconds of the span of time. Must be from -315,576,000,000 to
     # +315,576,000,000 inclusive. Note: these bounds are computed from: 60
@@ -957,7 +952,7 @@ class _Duration(Message):
         return ".".join(parts) + "s"
 
 
-@protoclass
+@dataclasses.dataclass
 class _Timestamp(Message):
     # Represents seconds of UTC time since Unix epoch 1970-01-01T00:00:00Z. Must
     # be from 0001-01-01T00:00:00Z to 9999-12-31T23:59:59Z inclusive.
@@ -1007,47 +1002,47 @@ class _WrappedMessage(Message):
         return self
 
 
-@protoclass
+@dataclasses.dataclass
 class _BoolValue(_WrappedMessage):
     value: bool = bool_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _Int32Value(_WrappedMessage):
     value: int = int32_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _UInt32Value(_WrappedMessage):
     value: int = uint32_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _Int64Value(_WrappedMessage):
     value: int = int64_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _UInt64Value(_WrappedMessage):
     value: int = uint64_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _FloatValue(_WrappedMessage):
     value: float = float_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _DoubleValue(_WrappedMessage):
     value: float = double_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _StringValue(_WrappedMessage):
     value: str = string_field(1)
 
 
-@protoclass
+@dataclasses.dataclass
 class _BytesValue(_WrappedMessage):
     value: bytes = bytes_field(1)
 

betterproto/templates/template.py

@@ -1,6 +1,7 @@
 # Generated by the protocol buffer compiler.  DO NOT EDIT!
 # sources: {{ ', '.join(description.files) }}
 # plugin: python-betterproto
+from dataclasses import dataclass
 {% if description.datetime_imports %}
 from datetime import {% for i in description.datetime_imports %}{{ i }}{% if not loop.last %}, {% endif %}{% endfor %}
 
@@ -37,7 +38,7 @@ class {{ enum.py_name }}(betterproto.Enum):
 {% endfor %}
 {% endif %}
 {% for message in description.messages %}
-@betterproto.protoclass
+@dataclass
 class {{ message.py_name }}(betterproto.Message):
     {% if message.comment %}
 {{ message.comment }}

betterproto/tests/test_features.py

@@ -4,11 +4,11 @@ from typing import Optional
 
 
 def test_has_field():
-    @betterproto.protoclass
+    @dataclass
     class Bar(betterproto.Message):
         baz: int = betterproto.int32_field(1)
 
-    @betterproto.protoclass
+    @dataclass
     class Foo(betterproto.Message):
         bar: Bar = betterproto.message_field(1)
 
@@ -34,11 +34,11 @@ def test_has_field():
 
 
 def test_class_init():
-    @betterproto.protoclass
+    @dataclass
     class Bar(betterproto.Message):
         name: str = betterproto.string_field(1)
 
-    @betterproto.protoclass
+    @dataclass
     class Foo(betterproto.Message):
         name: str = betterproto.string_field(1)
         child: Bar = betterproto.message_field(2)
@@ -53,7 +53,7 @@ def test_enum_as_int_json():
         ZERO = 0
         ONE = 1
 
-    @betterproto.protoclass
+    @dataclass
     class Foo(betterproto.Message):
         bar: TestEnum = betterproto.enum_field(1)
 
@@ -67,13 +67,13 @@ def test_enum_as_int_json():
 
 
 def test_unknown_fields():
-    @betterproto.protoclass
+    @dataclass
     class Newer(betterproto.Message):
         foo: bool = betterproto.bool_field(1)
         bar: int = betterproto.int32_field(2)
         baz: str = betterproto.string_field(3)
 
-    @betterproto.protoclass
+    @dataclass
     class Older(betterproto.Message):
         foo: bool = betterproto.bool_field(1)
 
@@ -89,11 +89,11 @@ def test_unknown_fields():
 
 
 def test_oneof_support():
-    @betterproto.protoclass
+    @dataclass
     class Sub(betterproto.Message):
         val: int = betterproto.int32_field(1)
 
-    @betterproto.protoclass
+    @dataclass
     class Foo(betterproto.Message):
         bar: int = betterproto.int32_field(1, group="group1")
         baz: str = betterproto.string_field(2, group="group1")
@@ -134,7 +134,7 @@ def test_oneof_support():
 
 
 def test_json_casing():
-    @betterproto.protoclass
+    @dataclass
     class CasingTest(betterproto.Message):
         pascal_case: int = betterproto.int32_field(1)
         camel_case: int = betterproto.int32_field(2)
@@ -165,7 +165,7 @@ def test_json_casing():
 
 
 def test_optional_flag():
-    @betterproto.protoclass
+    @dataclass
     class Request(betterproto.Message):
         flag: Optional[bool] = betterproto.message_field(1, wraps=betterproto.TYPE_BOOL)
 
@@ -180,7 +180,7 @@ def test_optional_flag():
 
 
 def test_to_dict_default_values():
-    @betterproto.protoclass
+    @dataclass
     class TestMessage(betterproto.Message):
         some_int: int = betterproto.int32_field(1)
         some_double: float = betterproto.double_field(2)
@@ -210,7 +210,7 @@ def test_to_dict_default_values():
     }
 
     # Some default and some other values
-    @betterproto.protoclass
+    @dataclass
     class TestMessage2(betterproto.Message):
         some_int: int = betterproto.int32_field(1)
         some_double: float = betterproto.double_field(2)
@@ -246,11 +246,11 @@ def test_to_dict_default_values():
     }
 
     # Nested messages
-    @betterproto.protoclass
+    @dataclass
     class TestChildMessage(betterproto.Message):
         some_other_int: int = betterproto.int32_field(1)
 
-    @betterproto.protoclass
+    @dataclass
     class TestParentMessage(betterproto.Message):
         some_int: int = betterproto.int32_field(1)
         some_double: float = betterproto.double_field(2)