[flake8-async] Do not lint yield in context manager cancel-scope-no-checkpoint (ASYNC100)

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

@@ -89,3 +89,16 @@ async def func():
 async def func():
     async with asyncio.timeout(delay=0.2), asyncio.timeout(delay=0.2):
         ...
+
+# Don't trigger for blocks with a yield statement
+async def foo():
+    with trio.fail_after(1):
+        yield
+
+# https://github.com/astral-sh/ruff/issues/12873
+@asynccontextmanager
+async def good_code():
+    with anyio.fail_after(10):
+        # There's no await keyword here, but we presume that there
+        # will be in the caller we yield to, so this is safe.
+        yield

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

@@ -10,6 +10,9 @@ use crate::rules::flake8_async::helpers::MethodName;
 /// ## What it does
 /// Checks for timeout context managers which do not contain a checkpoint.
 ///
+/// For the purposes of this check, `yield` is considered a checkpoint,
+/// since checkpoints may occur in the caller to which we yield.
+///
 /// ## Why is this bad?
 /// Some asynchronous context managers, such as `asyncio.timeout` and
 /// `trio.move_on_after`, have no effect unless they contain a checkpoint.
@@ -80,6 +83,17 @@ pub(crate) fn cancel_scope_no_checkpoint(
         return;
     }
 
+    // Treat yields as checkpoints, since checkpoints can happen
+    // in the caller yielded to.
+    // https://flake8-async.readthedocs.io/en/latest/rules.html#async100
+    // https://github.com/astral-sh/ruff/issues/12873
+    if with_stmt.body.iter().any(|stmt| {
+        stmt.as_expr_stmt()
+            .is_some_and(|expr| expr.value.is_yield_expr())
+    }) {
+        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);

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

@@ -98,4 +98,6 @@ ASYNC100.py:90:5: ASYNC100 A `with asyncio.timeout(...):` context does not conta
    |  _____^
 91 | |         ...
    | |___________^ ASYNC100
+92 |           
+93 |   # Don't trigger for blocks with a yield statement
    |