mypy: Enable local_partial_types.

dmypy is innately incompatible with `local_partial_types` being
`False` as it uses fined-grained incremental mode for caching.

We need to enable `local_partial_types` for mypy as well so that the two
will behave the same way.

This requires us to add additional type annotation in certain siuations
but that's fine.

Signed-off-by: Zixuan James Li <p359101898@gmail.com>

pyproject.toml

@@ -38,6 +38,10 @@ show_error_codes = true
 # Warn of unreachable or redundant code.
 warn_unreachable = true
 
+# dmypy enables local_partial_types implicitly. We need mypy to align
+# with this behavior.
+local_partial_types = true
+
 [[tool.mypy.overrides]]
 module = ["zproject.configured_settings", "zproject.settings"]
 no_implicit_reexport = false

tools/run-dev.py

@@ -338,7 +338,7 @@ def print_listeners() -> None:
     print()
 
 
-children = []
+children: List["subprocess.Popen[bytes]"] = []
 
 
 async def serve() -> None: