Fix type annotation for `before_request` and `before_app_request` decorators

CHANGES.rst

@@ -6,6 +6,8 @@ Version 2.0.2
 Unreleased
 
 -   Fix type annotation for ``teardown_request``. :issue:`4093`
+-   Fix type annotation for ``before_request`` and ``before_app_request``
+    decorators. :issue:`4104`
 
 
 Version 2.0.1

src/flask/app.py

@@ -59,6 +59,7 @@ from .signals import request_tearing_down
 from .templating import DispatchingJinjaLoader
 from .templating import Environment
 from .typing import AfterRequestCallable
+from .typing import BeforeFirstRequestCallable
 from .typing import BeforeRequestCallable
 from .typing import ErrorHandlerCallable
 from .typing import ResponseReturnValue
@@ -439,7 +440,7 @@ class Flask(Scaffold):
         #: :meth:`before_first_request` decorator.
         #:
         #: .. versionadded:: 0.8
-        self.before_first_request_funcs: t.List[BeforeRequestCallable] = []
+        self.before_first_request_funcs: t.List[BeforeFirstRequestCallable] = []
 
         #: A list of functions that are called when the application context
         #: is destroyed.  Since the application context is also torn down
@@ -1211,7 +1212,9 @@ class Flask(Scaffold):
         self.jinja_env.globals[name or f.__name__] = f
 
     @setupmethod
-    def before_first_request(self, f: BeforeRequestCallable) -> BeforeRequestCallable:
+    def before_first_request(
+        self, f: BeforeFirstRequestCallable
+    ) -> BeforeFirstRequestCallable:
         """Registers a function to be run before the first request to this
         instance of the application.
 

src/flask/blueprints.py

@@ -6,6 +6,7 @@ from .scaffold import _endpoint_from_view_func
 from .scaffold import _sentinel
 from .scaffold import Scaffold
 from .typing import AfterRequestCallable
+from .typing import BeforeFirstRequestCallable
 from .typing import BeforeRequestCallable
 from .typing import ErrorHandlerCallable
 from .typing import TeardownCallable
@@ -537,8 +538,8 @@ class Blueprint(Scaffold):
         return f
 
     def before_app_first_request(
-        self, f: BeforeRequestCallable
+        self, f: BeforeFirstRequestCallable
-    ) -> BeforeRequestCallable:
+    ) -> BeforeFirstRequestCallable:
         """Like :meth:`Flask.before_first_request`.  Such a function is
         executed before the first request to the application.
         """

src/flask/typing.py

@@ -35,7 +35,8 @@ ResponseReturnValue = t.Union[
 
 AppOrBlueprintKey = t.Optional[str]  # The App key is None, whereas blueprints are named
 AfterRequestCallable = t.Callable[["Response"], "Response"]
-BeforeRequestCallable = t.Callable[[], None]
+BeforeFirstRequestCallable = t.Callable[[], None]
+BeforeRequestCallable = t.Callable[[], t.Optional[ResponseReturnValue]]
 ErrorHandlerCallable = t.Callable[[Exception], ResponseReturnValue]
 TeardownCallable = t.Callable[[t.Optional[BaseException]], None]
 TemplateContextProcessorCallable = t.Callable[[], t.Dict[str, t.Any]]