drop support for Python 3.8

src/flask/app.py

@@ -1245,7 +1245,7 @@ class Flask(App):
 
         # extend existing headers with provided headers
         if headers:
-            rv.headers.update(headers)  # type: ignore[arg-type]
+            rv.headers.update(headers)
 
         return rv
 

src/flask/config.py

@@ -150,13 +150,13 @@ class Config(dict):  # type: ignore[type-arg]
         .. versionadded:: 2.1
         """
         prefix = f"{prefix}_"
-        len_prefix = len(prefix)
 
         for key in sorted(os.environ):
             if not key.startswith(prefix):
                 continue
 
             value = os.environ[key]
+            key = key.removeprefix(prefix)
 
             try:
                 value = loads(value)
@@ -164,9 +164,6 @@ class Config(dict):  # type: ignore[type-arg]
                 # Keep the value as a string if loading failed.
                 pass
 
-            # Change to key.removeprefix(prefix) on Python >= 3.9.
-            key = key[len_prefix:]
-
             if "__" not in key:
                 # A non-nested key, set directly.
                 self[key] = value

src/flask/helpers.py

@@ -5,7 +5,7 @@ import os
 import sys
 import typing as t
 from datetime import datetime
-from functools import lru_cache
+from functools import cache
 from functools import update_wrapper
 
 import werkzeug.utils
@@ -623,7 +623,7 @@ def get_root_path(import_name: str) -> str:
     return os.path.dirname(os.path.abspath(filepath))  # type: ignore[no-any-return]
 
 
-@lru_cache(maxsize=None)
+@cache
 def _split_blueprint_path(name: str) -> list[str]:
     out: list[str] = [name]
 

src/flask/sansio/scaffold.py

@@ -706,15 +706,6 @@ def _endpoint_from_view_func(view_func: ft.RouteCallable) -> str:
     return view_func.__name__
 
 
-def _path_is_relative_to(path: pathlib.PurePath, base: str) -> bool:
-    # Path.is_relative_to doesn't exist until Python 3.9
-    try:
-        path.relative_to(base)
-        return True
-    except ValueError:
-        return False
-
-
 def _find_package_path(import_name: str) -> str:
     """Find the path that contains the package or module."""
     root_mod_name, _, _ = import_name.partition(".")
@@ -745,7 +736,7 @@ def _find_package_path(import_name: str) -> str:
                 search_location = next(
                     location
                     for location in root_spec.submodule_search_locations
-                    if _path_is_relative_to(package_path, location)
+                    if package_path.is_relative_to(location)
                 )
             else:
                 # Pick the first path.
@@ -777,7 +768,7 @@ def find_package(import_name: str) -> tuple[str | None, str]:
     py_prefix = os.path.abspath(sys.prefix)
 
     # installed to the system
-    if _path_is_relative_to(pathlib.PurePath(package_path), py_prefix):
+    if pathlib.PurePath(package_path).is_relative_to(py_prefix):
         return py_prefix, package_path
 
     site_parent, site_folder = os.path.split(package_path)

src/flask/typing.py

@@ -12,7 +12,7 @@ ResponseValue = t.Union[
     "Response",
     str,
     bytes,
-    t.List[t.Any],
+    list[t.Any],
     # Only dict is actually accepted, but Mapping allows for TypedDict.
     t.Mapping[str, t.Any],
     t.Iterator[str],
@@ -21,21 +21,21 @@ ResponseValue = t.Union[
 
 # the possible types for an individual HTTP header
 # This should be a Union, but mypy doesn't pass unless it's a TypeVar.
-HeaderValue = t.Union[str, t.List[str], t.Tuple[str, ...]]
+HeaderValue = t.Union[str, list[str], tuple[str, ...]]
 
 # the possible types for HTTP headers
 HeadersValue = t.Union[
     "Headers",
     t.Mapping[str, HeaderValue],
-    t.Sequence[t.Tuple[str, HeaderValue]],
+    t.Sequence[tuple[str, HeaderValue]],
 ]
 
 # The possible types returned by a route function.
 ResponseReturnValue = t.Union[
     ResponseValue,
-    t.Tuple[ResponseValue, HeadersValue],
-    t.Tuple[ResponseValue, int],
-    t.Tuple[ResponseValue, int, HeadersValue],
+    tuple[ResponseValue, HeadersValue],
+    tuple[ResponseValue, int],
+    tuple[ResponseValue, int, HeadersValue],
     "WSGIApplication",
 ]
 
@@ -56,21 +56,21 @@ BeforeRequestCallable = t.Union[
     t.Callable[[], t.Optional[ResponseReturnValue]],
     t.Callable[[], t.Awaitable[t.Optional[ResponseReturnValue]]],
 ]
-ShellContextProcessorCallable = t.Callable[[], t.Dict[str, t.Any]]
+ShellContextProcessorCallable = t.Callable[[], dict[str, t.Any]]
 TeardownCallable = t.Union[
     t.Callable[[t.Optional[BaseException]], None],
     t.Callable[[t.Optional[BaseException]], t.Awaitable[None]],
 ]
 TemplateContextProcessorCallable = t.Union[
-    t.Callable[[], t.Dict[str, t.Any]],
-    t.Callable[[], t.Awaitable[t.Dict[str, t.Any]]],
+    t.Callable[[], dict[str, t.Any]],
+    t.Callable[[], t.Awaitable[dict[str, t.Any]]],
 ]
 TemplateFilterCallable = t.Callable[..., t.Any]
 TemplateGlobalCallable = t.Callable[..., t.Any]
 TemplateTestCallable = t.Callable[..., bool]
-URLDefaultCallable = t.Callable[[str, t.Dict[str, t.Any]], None]
+URLDefaultCallable = t.Callable[[str, dict[str, t.Any]], None]
 URLValuePreprocessorCallable = t.Callable[
-    [t.Optional[str], t.Optional[t.Dict[str, t.Any]]], None
+    [t.Optional[str], t.Optional[dict[str, t.Any]]], None
 ]
 
 # This should take Exception, but that either breaks typing the argument