Avoid unused async when context manager includes TaskGroup (#12605)

## Summary

Closes #12354.

crates/ruff_linter/resources/test/fixtures/flake8_async/ASYNC100.py

@@ -4,56 +4,61 @@
 
 
 async def func():
-    with trio.fail_after():
+    async with trio.fail_after():
         ...
 
 
 async def func():
-    with trio.fail_at():
+    async with trio.fail_at():
         await ...
 
 
 async def func():
-    with trio.move_on_after():
+    async with trio.move_on_after():
         ...
 
 
 async def func():
-    with trio.move_at():
+    async with trio.move_at():
         await ...
 
 
 async def func():
-    with trio.move_at():
-        async with trio.open_nursery() as nursery:
+    async with trio.move_at():
+        async with trio.open_nursery():
             ...
 
 
 async def func():
-    with anyio.move_on_after():
+    async with anyio.move_on_after(delay=0.2):
         ...
 
 
 async def func():
-    with anyio.fail_after():
+    async with anyio.fail_after():
         ...
 
 
 async def func():
-    with anyio.CancelScope():
+    async with anyio.CancelScope():
         ...
 
 
 async def func():
-    with anyio.CancelScope():
+    async with anyio.CancelScope():
         ...
 
 
 async def func():
-    with asyncio.timeout():
+    async with asyncio.timeout(delay=0.2):
         ...
 
 
 async def func():
-    with asyncio.timeout_at():
+    async with asyncio.timeout_at(when=0.2):
+        ...
+
+
+async def func():
+    async with asyncio.timeout(delay=0.2), asyncio.TaskGroup():
         ...

crates/ruff_linter/src/rules/flake8_async/rules/cancel_scope_no_checkpoint.rs

@@ -69,12 +69,31 @@ pub(crate) fn cancel_scope_no_checkpoint(
         return;
     }
 
+    // If the body contains an `await` statement, the context manager is used correctly.
     let mut visitor = AwaitVisitor::default();
     visitor.visit_body(&with_stmt.body);
     if visitor.seen_await {
         return;
     }
 
+    // If there's an `asyncio.TaskGroup()` context manager alongside the timeout, it's fine, as in:
+    // ```python
+    // async with asyncio.timeout(2.0), asyncio.TaskGroup():
+    //     ...
+    // ```
+    if with_items.iter().any(|item| {
+        item.context_expr.as_call_expr().is_some_and(|call| {
+            checker
+                .semantic()
+                .resolve_qualified_name(call.func.as_ref())
+                .is_some_and(|qualified_name| {
+                    matches!(qualified_name.segments(), ["asyncio", "TaskGroup"])
+                })
+        })
+    }) {
+        return;
+    }
+
     if matches!(checker.settings.preview, PreviewMode::Disabled) {
         if matches!(method_name.module(), AsyncModule::Trio) {
             checker.diagnostics.push(Diagnostic::new(

crates/ruff_linter/src/rules/flake8_async/snapshots/ruff_linter__rules__flake8_async__tests__ASYNC100_ASYNC100.py.snap

@@ -4,7 +4,7 @@ source: crates/ruff_linter/src/rules/flake8_async/mod.rs
 ASYNC100.py:7:5: ASYNC100 A `with trio.fail_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
   |
 6 |   async def func():
-7 |       with trio.fail_after():
+7 |       async with trio.fail_after():
   |  _____^
 8 | |         ...
   | |___________^ ASYNC100
@@ -13,7 +13,7 @@ ASYNC100.py:7:5: ASYNC100 A `with trio.fail_after(...):` context does not contai
 ASYNC100.py:17:5: ASYNC100 A `with trio.move_on_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 16 |   async def func():
-17 |       with trio.move_on_after():
+17 |       async with trio.move_on_after():
    |  _____^
 18 | |         ...
    | |___________^ ASYNC100

crates/ruff_linter/src/rules/flake8_async/snapshots/ruff_linter__rules__flake8_async__tests__preview__ASYNC100_ASYNC100.py.snap

@@ -4,7 +4,7 @@ source: crates/ruff_linter/src/rules/flake8_async/mod.rs
 ASYNC100.py:7:5: ASYNC100 A `with trio.fail_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
   |
 6 |   async def func():
-7 |       with trio.fail_after():
+7 |       async with trio.fail_after():
   |  _____^
 8 | |         ...
   | |___________^ ASYNC100
@@ -13,7 +13,7 @@ ASYNC100.py:7:5: ASYNC100 A `with trio.fail_after(...):` context does not contai
 ASYNC100.py:17:5: ASYNC100 A `with trio.move_on_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 16 |   async def func():
-17 |       with trio.move_on_after():
+17 |       async with trio.move_on_after():
    |  _____^
 18 | |         ...
    | |___________^ ASYNC100
@@ -22,7 +22,7 @@ ASYNC100.py:17:5: ASYNC100 A `with trio.move_on_after(...):` context does not co
 ASYNC100.py:33:5: ASYNC100 A `with anyio.move_on_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 32 |   async def func():
-33 |       with anyio.move_on_after():
+33 |       async with anyio.move_on_after(delay=0.2):
    |  _____^
 34 | |         ...
    | |___________^ ASYNC100
@@ -31,7 +31,7 @@ ASYNC100.py:33:5: ASYNC100 A `with anyio.move_on_after(...):` context does not c
 ASYNC100.py:38:5: ASYNC100 A `with anyio.fail_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 37 |   async def func():
-38 |       with anyio.fail_after():
+38 |       async with anyio.fail_after():
    |  _____^
 39 | |         ...
    | |___________^ ASYNC100
@@ -40,7 +40,7 @@ ASYNC100.py:38:5: ASYNC100 A `with anyio.fail_after(...):` context does not cont
 ASYNC100.py:43:5: ASYNC100 A `with anyio.CancelScope(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 42 |   async def func():
-43 |       with anyio.CancelScope():
+43 |       async with anyio.CancelScope():
    |  _____^
 44 | |         ...
    | |___________^ ASYNC100
@@ -49,7 +49,7 @@ ASYNC100.py:43:5: ASYNC100 A `with anyio.CancelScope(...):` context does not con
 ASYNC100.py:48:5: ASYNC100 A `with anyio.CancelScope(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 47 |   async def func():
-48 |       with anyio.CancelScope():
+48 |       async with anyio.CancelScope():
    |  _____^
 49 | |         ...
    | |___________^ ASYNC100
@@ -58,7 +58,7 @@ ASYNC100.py:48:5: ASYNC100 A `with anyio.CancelScope(...):` context does not con
 ASYNC100.py:53:5: ASYNC100 A `with asyncio.timeout(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 52 |   async def func():
-53 |       with asyncio.timeout():
+53 |       async with asyncio.timeout(delay=0.2):
    |  _____^
 54 | |         ...
    | |___________^ ASYNC100
@@ -67,7 +67,7 @@ ASYNC100.py:53:5: ASYNC100 A `with asyncio.timeout(...):` context does not conta
 ASYNC100.py:58:5: ASYNC100 A `with asyncio.timeout_at(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    |
 57 |   async def func():
-58 |       with asyncio.timeout_at():
+58 |       async with asyncio.timeout_at(when=0.2):
    |  _____^
 59 | |         ...
    | |___________^ ASYNC100