Improve MyPy configuration

Some improvments flagged by Repo-Review: https://learn.scientific-python.org/development/guides/repo-review/

1. Remove now-default show_error_codes.
2. Enable some optional error codes with extra checks.

pyproject.toml

@@ -75,9 +75,13 @@ source = [
 show_missing = true
 
 [tool.mypy]
+enable_error_code = [
+  "ignore-without-code",
+  "redundant-expr",
+  "truthy-bool",
+]
 mypy_path = "src/"
 namespace_packages = false
-show_error_codes = true
 strict = true
 warn_unreachable = true
 

src/django_upgrade/data.py

@@ -199,7 +199,7 @@ def decorator(func: ASTFunc[AST_T]) -> ASTFunc[AST_T]:
 
 def _import_fixers() -> None:
     # https://github.com/python/mypy/issues/1422
-    fixers_path: str = fixers.__path__  # type: ignore
+    fixers_path: str = fixers.__path__  # type: ignore [assignment]
     mod_infos = pkgutil.walk_packages(fixers_path, f"{fixers.__name__}.")
     for _, name, _ in mod_infos:
         __import__(name, fromlist=["_trash"])

src/django_upgrade/fixers/assert_form_error.py

@@ -161,8 +161,7 @@ def visit_Expr(self, node: ast.Expr) -> Any:
 
     def visit_Assign(self, node: ast.Assign) -> Any:
         if (
-            isinstance(node, ast.Assign)
-            and len(node.targets) == 1
+            len(node.targets) == 1
             and isinstance(node.targets[0], ast.Name)
             and node.targets[0].id == self.name
             and (

src/django_upgrade/fixers/request_headers.py

@@ -74,8 +74,7 @@ def visit_Compare(
     parents: list[ast.AST],
 ) -> Iterable[tuple[Offset, TokenFunc]]:
     if (
-        isinstance(node, ast.Compare)
-        and len(node.ops) == 1
+        len(node.ops) == 1
         and isinstance(node.ops[0], (ast.In, ast.NotIn))
         and len(node.comparators) == 1
         and is_request_or_self_request_meta(node.comparators[0])

src/django_upgrade/fixers/utils_timezone.py

@@ -57,8 +57,8 @@ def visit_Attribute(
         and isinstance(node.value, ast.Name)
         and node.value.id == "timezone"
         and "timezone" in state.from_imports["django.utils"]
-        and (details := get_import_details(state, parents[0]))
-        and details.datetime_module is not None
+        and (details := get_import_details(state, parents[0])).datetime_module
+        is not None
     ):
         new_src = f"{details.datetime_module}.timezone"
         yield ast_start_offset(node), partial(replace, src=new_src)