Add type annotations to _allocate() abstract method

Make BasePackageDef generic over pin type (PinType) and add proper
type annotations to the _allocate() abstract method. This fixes
pyright type checking errors where the return type was treated as
None instead of List[PinType].

Changes:
- BasePackageDef now inherits from Generic[PinType]
- LinearAllocPackageDef specifies BasePackageDef[int]
- GAPackageDef specifies BasePackageDef[GAPin]
- _allocate() signature includes proper type hints

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: robtaylor

chipflow_lib/packaging/.grid_array.py.swp

@@ -9,7 +9,7 @@
 
 import abc
 from collections import defaultdict
-from typing import TYPE_CHECKING, Dict, List, Set
+from typing import TYPE_CHECKING, Dict, Generic, List, Set, TypeVar
 
 import pydantic
 from amaranth.lib import wiring, io
@@ -24,8 +24,11 @@
 if TYPE_CHECKING:
     from ..config_models import Config, Process
 
+# Type variable for pin types (int for linear allocation, GAPin for grid arrays, etc.)
+PinType = TypeVar('PinType')
 
-class BasePackageDef(pydantic.BaseModel, abc.ABC):
+
+class BasePackageDef(pydantic.BaseModel, Generic[PinType], abc.ABC):
     """
     Abstract base class for the definition of a package.
 
@@ -166,7 +169,7 @@ def allocate_pins(self, config: 'Config', process: 'Process', lockfile: LockFile
         return LockFile(package=package, process=process, metadata=self._interfaces, port_map=portmap)
 
     @abc.abstractmethod
-    def _allocate(self, available, width: int):
+    def _allocate(self, available: Set[PinType], width: int) -> List[PinType]:
         """
         Allocate pins from available set.
 
@@ -206,7 +209,7 @@ def _sortpins(self, pins: Pins) -> PinList:
         return sorted(list(pins))
 
 
-class LinearAllocPackageDef(BasePackageDef):
+class LinearAllocPackageDef(BasePackageDef[int]):
     """
     Base class for package types with linear pin/pad allocation.
 

chipflow_lib/packaging/base.py

@@ -36,7 +36,7 @@ class GALayout(StrEnum):
     ISLAND = auto()  # Perimeter + center island
 
 
-class GAPackageDef(BasePackageDef):
+class GAPackageDef(BasePackageDef[GAPin]):
     """
     Definition of a grid array package.