Enable --warn-redundant-casts option in mypy

changelog.d/14671.misc

@@ -0,0 +1 @@
+Improve type hints.

mypy.ini

@@ -12,6 +12,7 @@ local_partial_types = True
 no_implicit_optional = True
 disallow_untyped_defs = True
 strict_equality = True
+warn_redundant_casts = True
 
 files =
  docker/,

scripts-dev/release.py

@@ -27,7 +27,7 @@
 import urllib.request
 from os import path
 from tempfile import TemporaryDirectory
-from typing import Any, List, Optional, cast
+from typing import Any, List, Optional
 
 import attr
 import click
@@ -174,9 +174,7 @@ def _prepare() -> None:
  click.get_current_context().abort()
 
  # Switch to the release branch.
- # Cast safety: parse() won't return a version.LegacyVersion from our
- # version string format.
- parsed_new_version = cast(version.Version, version.parse(new_version))
+ parsed_new_version = version.parse(new_version)
 
  # We assume for debian changelogs that we only do RCs or full releases.
  assert not parsed_new_version.is_devrelease

synapse/storage/database.py

@@ -667,7 +667,8 @@ def new_transaction(
  )
  # also check variables referenced in func's closure
  if inspect.isfunction(func):
- f = cast(types.FunctionType, func)
+ # Keep the cast for now---it helps PyCharm to understand what `func` is.
+ f = cast(types.FunctionType, func) # type: ignore[redundant-cast]
  if f.__closure__:
  for i, cell in enumerate(f.__closure__):
  if inspect.isgenerator(cell.cell_contents):

synapse/storage/engines/postgres.py

@@ -77,7 +77,7 @@ def check_database(
  # docs: The number is formed by converting the major, minor, and
  # revision numbers into two-decimal-digit numbers and appending them
  # together. For example, version 8.1.5 will be returned as 80105
- self._version = cast(int, db_conn.server_version)
+ self._version = db_conn.server_version
  allow_unsafe_locale = self.config.get("allow_unsafe_locale", False)
 
  # Are we on a supported PostgreSQL version?