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.

1 files changed, 3 insertions, 1 deletions

diff --git a/mesonbuild/interpreterbase/interpreterbase.py b/mesonbuild/interpreterbase/interpreterbase.py
index 99f6619..bd7d7f9 100644
--- a/mesonbuild/interpreterbase/interpreterbase.py
+++ b/mesonbuild/interpreterbase/interpreterbase.py
@@ -26,6 +26,8 @@ from .baseobjects import (
     ObjectHolder,
     IterableObject,
 
+    SubProject,
+
     TYPE_var,
     TYPE_kwargs,
 
@@ -73,7 +75,7 @@ FunctionType = T.Dict[
 ]
 
 class InterpreterBase:
-    def __init__(self, source_root: str, subdir: str, subproject: str):
+    def __init__(self, source_root: str, subdir: str, subproject: 'SubProject'):
         self.source_root = source_root
         self.funcs: FunctionType = {}
         self.builtin: T.Dict[str, InterpreterObject] = {}