feat: implement iterate_annotation_chain to allow subclassing in type structs

Author: MrIndeciso

libdestruct/common/struct/struct_impl.py

@@ -13,6 +13,7 @@
 from libdestruct.common.obj import obj
 from libdestruct.common.struct import struct
 from libdestruct.common.type_registry import TypeRegistry
+from libdestruct.common.utils import iterate_annotation_chain
 
 if TYPE_CHECKING:  # pragma: no cover
     from libdestruct.backing.resolver import Resolver
@@ -52,7 +53,7 @@ def _inflate_struct_attributes(
     ) -> None:
         current_offset = 0
 
-        for name, annotation in reference_type.__annotations__.items():
+        for name, annotation in iterate_annotation_chain(reference_type, terminate_at=struct):
             if name in reference_type.__dict__:
                 # Field associated with the annotation
                 attrs = getattr(reference_type, name)
@@ -97,7 +98,7 @@ def compute_own_size(cls: type[struct_impl], reference_type: type) -> None:
         """Compute the size of the struct."""
         size = 0
 
-        for name, annotation in reference_type.__annotations__.items():
+        for name, annotation in iterate_annotation_chain(reference_type, terminate_at=struct):
             if name in reference_type.__dict__:
                 # Field associated with the annotation
                 attrs = getattr(reference_type, name)

libdestruct/common/struct/struct_inflater.py

@@ -18,7 +18,7 @@ def inflate_struct_type(reference_type: type[struct]) -> type[struct_impl]:
     if issubclass(reference_type, struct_impl):
         return reference_type
 
-    type_impl = type(reference_type.__name__, (struct_impl,), {"_members": {}})
+    type_impl = type(reference_type.__name__, (struct_impl, reference_type), {"_members": {}})
     type_impl._reference_struct = reference_type
 
     reference_type._type_impl = type_impl

libdestruct/common/type_registry.py

@@ -75,12 +75,14 @@ def inflater_for(
     def _inflater_for_type(self: TypeRegistry, item: type[obj]) -> type[obj]:
         parent = item.__base__
 
-        for handler in self.type_handlers.get(parent, []):
-            result = handler(item)
-
-            if result is not None:
-                self.mapping[item] = result
-                return result
+        while parent:
+            for handler in self.type_handlers.get(parent, []):
+                result = handler(item)
+
+                if result is not None:
+                    self.mapping[item] = result
+                    return result
+            parent = parent.__base__
 
         raise ValueError(f"No applicable inflater found for {item}")
 

libdestruct/common/utils.py

@@ -7,11 +7,13 @@
 from __future__ import annotations
 
 from types import MethodType
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 from libdestruct.common.field import Field
 
 if TYPE_CHECKING:  # pragma: no cover
+    from collections.abc import Generator
+
     from libdestruct.backing.resolver import Resolver
     from libdestruct.common.obj import obj
 
@@ -32,3 +34,11 @@ def size_of(item_or_inflater: obj | callable[[Resolver], obj]) -> int:
         return field_object.get_size()
 
     raise ValueError(f"Cannot determine the size of {item_or_inflater}")
+
+
+def iterate_annotation_chain(item: obj, terminate_at: object | None = None) -> Generator[tuple[str, Any]]:
+    """Iterate over the annotation chain of the provided item."""
+    current_item = item
+    while current_item is not terminate_at:
+        yield from current_item.__annotations__.items()
+        current_item = current_item.__base__ if hasattr(current_item, "__base__") else None