Typing updates

changes/2252.feature.rst

@@ -0,0 +1 @@
+The typing for Toga's API surface was updated to be more precise.

core/src/toga/__init__.py

@@ -1,4 +1,7 @@
+from __future__ import annotations
+
 import warnings
+from pathlib import Path
 
 from .app import App, DocumentApp, DocumentMainWindow, MainWindow
 
@@ -49,7 +52,7 @@ class NotImplementedWarning(RuntimeWarning):
     # single argument (the warning message). Use a factory method to avoid reproducing
     # the message format and the warn invocation.
     @classmethod
-    def warn(self, platform, feature):
+    def warn(cls, platform: str, feature: str) -> None:
         """Raise a warning that a feature isn't implemented on a platform."""
         warnings.warn(NotImplementedWarning(f"[{platform}] Not implemented: {feature}"))
 
@@ -116,7 +119,7 @@ def warn(self, platform, feature):
 ]
 
 
-def _package_version(file, name):
+def _package_version(file: Path | str | None, name: str) -> str:
     try:
         # Read version from SCM metadata
         # This will only exist in a development environment