RLP fields using annotated class attributes

.circleci/config.yml

@@ -52,6 +52,12 @@ jobs:
       - image: circleci/python:3.6
         environment:
           TOXENV: py36-core
+  py37-core:
+    <<: *common
+    docker:
+      - image: circleci/python:3.7
+        environment:
+          TOXENV: py37-core
   pypy3-core:
     <<: *common
     docker:
@@ -71,6 +77,12 @@ jobs:
       - image: circleci/python:3.6
         environment:
           TOXENV: py36-doctest
+  py37-doctest:
+    <<: *common
+    docker:
+      - image: circleci/python:3.7
+        environment:
+          TOXENV: py37-doctest
   pypy3-doctest:
     <<: *common
     docker:
@@ -91,10 +103,12 @@ workflows:
     jobs:
       - py35-core
       - py36-core
+      - py37-core
       - pypy3-core
 
       - py35-doctest
       - py36-doctest
+      - py37-doctest
       - pypy3-doctest
 
       - lint

rlp/sedes/serializable.py

@@ -368,8 +368,23 @@ def __new__(cls, name, bases, attrs):
             # If this is the original creation of the `Serializable` class,
             # just create the class.
             return super_new(cls, name, bases, attrs)
+
+        # The class being constructed is a subclass of `Serializable`.
+
+        annotated_fields = tuple(
+            (field, sede)
+            for field, sede in attrs.get('__annotations__', {}).items()
+            if hasattr(sede, 'serialize') and hasattr(sede, 'deserialize')
+        )
+
+        if declares_fields and annotated_fields:
+            raise TypeError(
+                f"{name} defines both a 'fields' attribute as well as annotated fields."
+            )
         elif not declares_fields:
-            if has_multiple_serializable_parents:
+            if annotated_fields:
+                fields = annotated_fields
+            elif has_multiple_serializable_parents:
                 raise TypeError(
                     "Cannot create subclass from multiple parent `Serializable` "
                     "classes without explicit `fields` declaration."