From 8727e37e0dd342c55a74ae9c3ef517e42ae44650 Mon Sep 17 00:00:00 2001
From: Ash <73482956+ascopes@users.noreply.github.com>
Date: Fri, 10 Oct 2025 15:50:43 +0100
Subject: [PATCH 1/2] Fix issue where no anyio backend is produced

FIxes an issue where running the outer group produces
an exception "RuntimeError: Backend None Unknown".

If no anyio backend is specified, then asyncio is used as
the default.
---
 src/asyncclick/core.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/asyncclick/core.py b/src/asyncclick/core.py
index 7688904a1..15a3c73be 100644
--- a/src/asyncclick/core.py
+++ b/src/asyncclick/core.py
@@ -1520,7 +1520,7 @@ async def _main_shell_completion(
     def __call__(
         self,
         *args: t.Any,
-        _anyio_backend: str | None = None,
+        _anyio_backend: str = "asyncio",
         _anyio_backend_options: dict[str, t.Any] | None = None,
         **kwargs: t.Any,
     ) -> t.Any:

From 8e870cd5dd3f50c8e8a0763dd591db2c84e97242 Mon Sep 17 00:00:00 2001
From: Ash <73482956+ascopes@users.noreply.github.com>
Date: Fri, 10 Oct 2025 15:54:05 +0100
Subject: [PATCH 2/2] Update core.py to move asyncio fallback logic to preseve
 existing behaviour

---
 src/asyncclick/core.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/asyncclick/core.py b/src/asyncclick/core.py
index 15a3c73be..621617835 100644
--- a/src/asyncclick/core.py
+++ b/src/asyncclick/core.py
@@ -1520,7 +1520,7 @@ async def _main_shell_completion(
     def __call__(
         self,
         *args: t.Any,
-        _anyio_backend: str = "asyncio",
+        _anyio_backend: str | None,
         _anyio_backend_options: dict[str, t.Any] | None = None,
         **kwargs: t.Any,
     ) -> t.Any:
@@ -1529,6 +1529,9 @@ def __call__(
         If you are already inside an async event loop, call
         ``await`` :meth:`main` instead.
 
+        If no backend is found and anyio is not installed, then ``asyncio`` is
+        used for the backend.
+
         :param _anyio_backend: The backend to use for the event loop.
         :param _anyio_backend_options: Any options to pass to the backend.
 
@@ -1553,7 +1556,7 @@ def __call__(
             import trio
 
             return trio.run(self._main, main, args, kwargs)
-        if _anyio_backend == "asyncio":
+        if _anyio_backend == "asyncio" or _anyio_backend is None:
             import asyncio
 
             return asyncio.run(self._main(main, args, kwargs))