2 files changed, 39 insertions, 0 deletions
diff --git a/src/test/ui/lint/must_not_suspend/mutex.rs b/src/test/ui/lint/must_not_suspend/mutex.rs
new file mode 100644
index 00000000000..7bb895e7d36
--- /dev/null
+++ b/src/test/ui/lint/must_not_suspend/mutex.rs
@@ -0,0 +1,13 @@
+// edition:2018
+#![feature(must_not_suspend)]
+#![deny(must_not_suspend)]
+
+async fn other() {}
+
+pub async fn uhoh(m: std::sync::Mutex<()>) {
+    let _guard = m.lock().unwrap(); //~ ERROR `MutexGuard` held across
+    other().await;
+}
+
+fn main() {
+}
diff --git a/src/test/ui/lint/must_not_suspend/mutex.stderr b/src/test/ui/lint/must_not_suspend/mutex.stderr
new file mode 100644
index 00000000000..69638fc2010
--- /dev/null
+++ b/src/test/ui/lint/must_not_suspend/mutex.stderr
@@ -0,0 +1,26 @@
+error: `MutexGuard` held across a suspend point, but should not be
+  --> $DIR/mutex.rs:8:9
+   |
+LL |     let _guard = m.lock().unwrap();
+   |         ^^^^^^
+LL |     other().await;
+   |     ------------- the value is held across this suspend point
+   |
+note: the lint level is defined here
+  --> $DIR/mutex.rs:3:9
+   |
+LL | #![deny(must_not_suspend)]
+   |         ^^^^^^^^^^^^^^^^
+note: Holding a MutexGuard across suspend points can cause deadlocks, delays, and cause Future's to not implement `Send`
+  --> $DIR/mutex.rs:8:9
+   |
+LL |     let _guard = m.lock().unwrap();
+   |         ^^^^^^
+help: consider using a block (`{ ... }`) to shrink the value's scope, ending before the suspend point
+  --> $DIR/mutex.rs:8:9
+   |
+LL |     let _guard = m.lock().unwrap();
+   |         ^^^^^^
+
+error: aborting due to previous error
+