Share the nominal key declaration overlap contract

src/textual/keys.py

@@ -3,7 +3,7 @@
 import unicodedata
 import inspect
 import re
-from abc import ABC, abstractmethod
+from abc import ABC, ABCMeta, abstractmethod
 from typing import TYPE_CHECKING, Callable, ClassVar, Generic, Iterator, TypeVar
 from enum import Enum
 from dataclasses import dataclass
@@ -18,6 +18,14 @@
 NodeT = TypeVar("NodeT", bound="DOMNode", contravariant=True)
 
 
+class KeyDeclarationType(ABCMeta):
+    """A key-declaring class, including declarations supplied by a metaclass."""
+
+    def permits_key_overlap(cls, other: KeyDeclarationType) -> bool:
+        """An explicitly declared alternative may share this declaration's key."""
+        return False
+
+
 class KeyInvocation(ABC):
     """The concrete command a binding invokes, independent of its active mode."""
 
@@ -51,7 +59,7 @@ def visible_for_focus(self, mode: type[EditingMode], focused: frozenset[str]) ->
     def permits_invocation_overlap(self, other: KeyInvocation) -> bool:
         return False
 
-    def overlaps_declaration(self, other: type[KeyDeclaration]) -> bool:
+    def overlaps_declaration(self, other: KeyDeclarationType) -> bool:
         return False
 
 
@@ -62,7 +70,7 @@ def __get__(self, instance: object, owner: type[KeyDeclaration]) -> str:
         return owner.default_title()
 
 
-class KeyDeclaration(KeyInvocation, Generic[NodeT]):
+class KeyDeclaration(KeyInvocation, Generic[NodeT], metaclass=KeyDeclarationType):
     """Shared metadata for application actions and native editor commands.
 
     Each provider retains its existing family registry. This view discovers the
@@ -109,7 +117,7 @@ def key_system(self) -> bool:
     def permits_invocation_overlap(self, other: KeyInvocation) -> bool:
         return other.overlaps_declaration(type(self))
 
-    def overlaps_declaration(self, other: type[KeyDeclaration]) -> bool:
+    def overlaps_declaration(self, other: KeyDeclarationType) -> bool:
         return type(self).permits_key_overlap(other)
 
     @abstractmethod
@@ -125,11 +133,6 @@ def bindings_for(cls, mode: type[EditingMode]) -> tuple[Binding, ...]:
     def summary(cls) -> str:
         return inspect.cleandoc(cls.__doc__ or "")
 
-    @classmethod
-    def permits_key_overlap(cls, other: type[KeyDeclaration]) -> bool:
-        """An explicitly declared alternative may share a key with another declaration."""
-        return False
-
     @classmethod
     def declarations(cls) -> Iterator[type[KeyDeclaration]]:
         """Project each key family from the declaration owner's registry."""