FeatureNew: add mypy type annotations for subproject arg

Use a derived type when passing `subproject` around, so that mypy knows
it's actually a SubProject, not a str. This means that passing anything
other than a handle to the interpreter state's subproject attribute
becomes a type violation, specifically when the order of the *four*
different str arguments is typoed.

2 files changed, 6 insertions, 2 deletions

diff --git a/mesonbuild/interpreter/interpreterobjects.py b/mesonbuild/interpreter/interpreterobjects.py
index 6b7cbcd..989877e 100644
--- a/mesonbuild/interpreter/interpreterobjects.py
+++ b/mesonbuild/interpreter/interpreterobjects.py
@@ -31,6 +31,7 @@ if T.TYPE_CHECKING:
     from . import kwargs
     from .interpreter import Interpreter
     from ..envconfig import MachineInfo
+    from ..interpreterbase import SubProject
 
     from typing_extensions import TypedDict
 
@@ -40,7 +41,7 @@ if T.TYPE_CHECKING:
 
 
 def extract_required_kwarg(kwargs: 'kwargs.ExtractRequired',
-                           subproject: str,
+                           subproject: 'SubProject',
                            feature_check: T.Optional[FeatureCheckBase] = None,
                            default: bool = True) -> T.Tuple[bool, bool, T.Optional[str]]:
     val = kwargs.get('required', default)
diff --git a/mesonbuild/interpreter/primitives/range.py b/mesonbuild/interpreter/primitives/range.py
index 9054278..a35470c 100644
--- a/mesonbuild/interpreter/primitives/range.py
+++ b/mesonbuild/interpreter/primitives/range.py
@@ -10,8 +10,11 @@ from ...interpreterbase import (
     InvalidArguments,
 )
 
+if T.TYPE_CHECKING:
+    from ...interpreterbase import SubProject
+
 class RangeHolder(MesonInterpreterObject, IterableObject):
-    def __init__(self, start: int, stop: int, step: int, *, subproject: str) -> None:
+    def __init__(self, start: int, stop: int, step: int, *, subproject: 'SubProject') -> None:
         super().__init__(subproject=subproject)
         self.range = range(start, stop, step)
         self.operators.update({