use asyncio.run in Template.render (#1952)

Author: davidism

CHANGES.rst

@@ -5,6 +5,9 @@ Version 3.1.5
 
 Unreleased
 
+-   Calling sync ``render`` for an async template uses ``asyncio.run``.
+    :pr:`1952`
+
 
 Version 3.1.4
 -------------
@@ -138,9 +141,8 @@ Released 2021-05-18
     extensions shows more relevant context. :issue:`1429`
 -   Fixed calling deprecated ``jinja2.Markup`` without an argument.
     Use ``markupsafe.Markup`` instead. :issue:`1438`
--   Calling sync ``render`` for an async template uses ``asyncio.run``
-    on Python >= 3.7. This fixes a deprecation that Python 3.10
-    introduces. :issue:`1443`
+-   Calling sync ``render`` for an async template uses ``asyncio.new_event_loop``
+    This fixes a deprecation that Python 3.10 introduces. :issue:`1443`
 
 
 Version 3.0.0

docs/api.rst

@@ -515,9 +515,6 @@ environment to compile different code behind the scenes in order to
 handle async and sync code in an asyncio event loop. This has the
 following implications:
 
--   Template rendering requires an event loop to be available to the
-    current thread. :func:`asyncio.get_running_loop` must return an
-    event loop.
 -   The compiled code uses ``await`` for functions and attributes, and
     uses ``async for`` loops. In order to support using both async and
     sync functions in this context, a small wrapper is placed around

src/jinja2/environment.py

@@ -1282,19 +1282,7 @@ def render(self, *args: t.Any, **kwargs: t.Any) -> str:
         if self.environment.is_async:
             import asyncio
 
-            close = False
-
-            try:
-                loop = asyncio.get_running_loop()
-            except RuntimeError:
-                loop = asyncio.new_event_loop()
-                close = True
-
-            try:
-                return loop.run_until_complete(self.render_async(*args, **kwargs))
-            finally:
-                if close:
-                    loop.close()
+            return asyncio.run(self.render_async(*args, **kwargs))
 
         ctx = self.new_context(dict(*args, **kwargs))