mypy: enable allow-redefinition-new and fix fallout

Reduces 3 errors that show up in newer mypy versions than pinned in CI.

It is new since 1.16 and a likely future default for mypy 2.0. It allows
things like:

```
for i in ['one', 'two', 'three']:
    frob_a(i)

for i in [1, 2, 3]:
    frob_b(i)
```

since "i" is obviously used as a loop holder and its type can be freely
reinvented. Note: allow-redefinition-new isn't actually about this at
all, it has greater scope than loop holders and allows redefining
"unannotated variables" of all kinds. No granularity in what to accept
redefinition of. :P

To enable this, we must also opt in to local-partial-types, which has
some overlap with None-safety. Specifically:

> the most common cases for partial types are variables initialized
> using None, but without explicit X | None annotations. By default, mypy
> won’t check partial types spanning module top level or class top level.
> This flag changes the behavior to only allow partial types at local
> level, therefore it disallows inferring variable type for None from two
> assignments in different scopes.

So with this, we also fix a couple of actual type errors this revealed.
Where possible, stop None-initializing at all -- it's not strictly
needed for global variables, anyway, and it's a coding error if it is
possible to hit these variables without defining them first.

Bug: https://github.com/python/mypy/issues/19280

1 files changed, 5 insertions, 5 deletions

diff --git a/run_project_tests.py b/run_project_tests.py
index b2442703e..7067bfa0b 100755
--- a/run_project_tests.py
+++ b/run_project_tests.py
@@ -1577,11 +1577,11 @@ def detect_tools(report: bool = True) -> None:
         print('{0:<{2}}: {1}'.format(tool.tool, get_version(tool), max_width))
     print()
 
-symlink_test_dir1 = None
-symlink_test_dir2 = None
-symlink_file1 = None
-symlink_file2 = None
-symlink_file3 = None
+symlink_test_dir1: T.Optional[Path] = None
+symlink_test_dir2: T.Optional[Path] = None
+symlink_file1: T.Optional[Path] = None
+symlink_file2: T.Optional[Path] = None
+symlink_file3: T.Optional[Path] = None
 
 def scan_test_data_symlinks() -> None:
     global symlink_test_dir1, symlink_test_dir2, symlink_file1, symlink_file2, symlink_file3