From 1b552d0b0163e1c1ae3d4895438a9ce2b2bc098e Mon Sep 17 00:00:00 2001
From: David Lord <davidism@gmail.com>
Date: Thu, 11 Nov 2021 16:12:08 -0800
Subject: [PATCH] remove ContextVar compat

---
 docs/async-await.rst   |  9 +++++++--
 docs/installation.rst  | 12 ++++++++++++
 requirements/dev.txt   |  2 +-
 requirements/tests.in  |  2 +-
 requirements/tests.txt |  2 +-
 src/flask/app.py       |  8 --------
 6 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/docs/async-await.rst b/docs/async-await.rst
index 71e5f452..4c70f961 100644
--- a/docs/async-await.rst
+++ b/docs/async-await.rst
@@ -7,8 +7,7 @@ Using ``async`` and ``await``
 
 Routes, error handlers, before request, after request, and teardown
 functions can all be coroutine functions if Flask is installed with the
-``async`` extra (``pip install flask[async]``). It requires Python 3.7+
-where ``contextvars.ContextVar`` is available. This allows views to be
+``async`` extra (``pip install flask[async]``). This allows views to be
 defined with ``async def`` and use ``await``.
 
 .. code-block:: python
@@ -30,6 +29,12 @@ well as all the HTTP method handlers in views that inherit from the
     something like ``ValueError: set_wakeup_fd only works in main thread``,
     please upgrade to Python 3.9.
 
+.. admonition:: Using ``async`` with greenlet
+
+    When using gevent or eventlet to serve an application or patch the
+    runtime, greenlet>=1.0 is required. When using PyPy, PyPy>=7.3.7 is
+    required.
+
 
 Performance
 -----------
diff --git a/docs/installation.rst b/docs/installation.rst
index 6007bbb7..8a338e18 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -49,6 +49,18 @@ use them if you install them.
 .. _watchdog: https://pythonhosted.org/watchdog/
 
 
+greenlet
+~~~~~~~~
+
+You may choose to use gevent or eventlet with your application. In this
+case, greenlet>=1.0 is required. When using PyPy, PyPy>=7.3.7 is
+required.
+
+These are not minimum supported versions, they only indicate the first
+versions that added necessary features. You should use the latest
+versions of each.
+
+
 Virtual environments
 --------------------
 
diff --git a/requirements/dev.txt b/requirements/dev.txt
index b87571ff..33493af3 100644
--- a/requirements/dev.txt
+++ b/requirements/dev.txt
@@ -38,7 +38,7 @@ filelock==3.3.2
     # via
     #   tox
     #   virtualenv
-greenlet==1.1.2
+greenlet==1.1.2 ; python_version < "3.11"
     # via -r requirements/tests.in
 identify==2.3.3
     # via pre-commit
diff --git a/requirements/tests.in b/requirements/tests.in
index 88fe5481..41936997 100644
--- a/requirements/tests.in
+++ b/requirements/tests.in
@@ -1,5 +1,5 @@
 pytest
 asgiref
 blinker
-greenlet
+greenlet ; python_version < "3.11"
 python-dotenv
diff --git a/requirements/tests.txt b/requirements/tests.txt
index a86b6041..4e4247f5 100644
--- a/requirements/tests.txt
+++ b/requirements/tests.txt
@@ -10,7 +10,7 @@ attrs==21.2.0
     # via pytest
 blinker==1.4
     # via -r requirements/tests.in
-greenlet==1.1.2
+greenlet==1.1.2 ; python_version < "3.11"
     # via -r requirements/tests.in
 iniconfig==1.1.1
     # via pytest
diff --git a/src/flask/app.py b/src/flask/app.py
index 23b99e2c..7c4076c5 100644
--- a/src/flask/app.py
+++ b/src/flask/app.py
@@ -16,7 +16,6 @@ from werkzeug.exceptions import BadRequest
 from werkzeug.exceptions import BadRequestKeyError
 from werkzeug.exceptions import HTTPException
 from werkzeug.exceptions import InternalServerError
-from werkzeug.local import ContextVar
 from werkzeug.routing import BuildError
 from werkzeug.routing import Map
 from werkzeug.routing import MapAdapter
@@ -1621,13 +1620,6 @@ class Flask(Scaffold):
                 "Install Flask with the 'async' extra in order to use async views."
             ) from None
 
-        # Check that Werkzeug isn't using its fallback ContextVar class.
-        if ContextVar.__module__ == "werkzeug.local":
-            raise RuntimeError(
-                "Async cannot be used with this combination of Python "
-                "and Greenlet versions."
-            )
-
         return asgiref_async_to_sync(func)
 
     def make_response(self, rv: ResponseReturnValue) -> Response: