build: Use ImmutableSetProtocol for lru_cache'd value
To avoid mutation if possible.
@@ -40,7 +40,7 @@ from .linkers import StaticLinker
from .interpreterbase import FeatureNew
if T.TYPE_CHECKING:
- from ._typing import ImmutableListProtocol
+ from ._typing import ImmutableListProtocol, ImmutableSetProtocol
from .interpreter.interpreter import Test, SourceOutputs
from .mesonlib import FileMode, FileOrString
from .backend.backends import Backend
@@ -931,7 +931,7 @@ class BuildTarget(Target):
return result
@lru_cache(maxsize=None)
- def get_link_dep_subdirs(self):
+ def get_link_dep_subdirs(self) -> 'ImmutableSetProtocol[str]':
result: OrderedSet[str] = OrderedSet()
for i in self.link_targets:
if not isinstance(i, StaticLibrary):
