some more comments

python_modules/dagster/dagster/_config/structured_config.py

@@ -131,17 +131,29 @@ class _Temp(Generic[T]):
 
 @dataclass_transform()
 class BaseResourceMeta(pydantic.main.ModelMetaclass):
+    """
+    Custom metaclass for Resource and PartialResource. This metaclass is responsible for
+    transforming the type annotations on the class to allow for partially configured resources.
+    """
+
     def __new__(self, name, bases, namespaces, **kwargs):
+        # Gather all type annotations from the class and its base classes
         annotations = namespaces.get("__annotations__", {})
         for base in bases:
             if hasattr(base, "__annotations__"):
                 annotations.update(base.__annotations__)
         for field in annotations:
             if not field.startswith("__"):
+                # Check if the annotation is a ResourceDependency
                 if get_origin(annotations[field]) == _ResourceDep:
                     arg = get_args(annotations[field])[0]
+                    # If so, we treat it as a Union of a PartialResource and a Resource
+                    # for Pydantic's sake.
                     annotations[field] = Union[_PartialResource[arg], _Resource[arg]]
                 elif _safe_is_subclass(annotations[field], _Resource):
+                    # If the annotation is a Resource, we treat it as a Union of a PartialResource
+                    # and a Resource for Pydantic's sake, so that a user can pass in a partially
+                    # configured resource.
                     base = annotations[field]
                     annotations[field] = Union[_PartialResource[base], base]
 

python_modules/dagster/dagster_tests/core_tests/resource_tests/test_struct_config_resources.py

@@ -139,30 +139,30 @@ def another_asset(greeting: GreetingResource, hello_world_asset):
 def test_abc_resource():
     out_txt = []
 
-    class WriterResource(Resource, ABC):
+    class Writer(Resource, ABC):
         @abstractmethod
         def output(self, text: str) -> None:
             pass
 
-    class PrefixedWriterResource(WriterResource):
+    class PrefixedWriterResource(Writer):
         prefix: str
 
         def output(self, text: str) -> None:
             out_txt.append(f"{self.prefix}{text}")
 
-    class RepetitiveWriterResource(WriterResource):
+    class RepetitiveWriterResource(Writer):
         repetitions: int
 
         def output(self, text: str) -> None:
             out_txt.append(f"{text} " * self.repetitions)
 
     @op
-    def hello_world_op(writer: WriterResource):
+    def hello_world_op(writer: Writer):
         writer.output("hello, world!")
 
     # Can't instantiate abstract class
     with pytest.raises(TypeError):
-        WriterResource()  # pylint: disable=abstract-class-instantiated
+        Writer()  # pylint: disable=abstract-class-instantiated
 
     @job(resource_defs={"writer": PrefixedWriterResource(prefix="greeting: ")})
     def prefixed_job():
@@ -356,18 +356,25 @@ def hello_world_asset(writer: WriterResource):
 def test_nested_resources():
     out_txt = []
 
-    class WriterResource(Resource):
+    class Writer(Resource, ABC):
+        @abstractmethod
+        def output(self, text: str) -> None:
+            pass
+
+    class WriterResource(Writer):
         def output(self, text: str) -> None:
             out_txt.append(text)
 
-    class PrefixedWriterResource(WriterResource, Resource):
+    class PrefixedWriterResource(Writer):
         prefix: str
 
         def output(self, text: str) -> None:
             out_txt.append(f"{self.prefix}{text}")
 
-    class JsonWriterResource(WriterResource):
-        base_writer: WriterResource
+    class JsonWriterResource(
+        Writer,
+    ):
+        base_writer: Writer
         indent: int
 
         def output(self, obj: Any) -> None: