Implement let_underscore_future

2 files changed, 47 insertions, 0 deletions

diff --git a/tests/ui/let_underscore_future.rs b/tests/ui/let_underscore_future.rs
new file mode 100644
index 00000000000..d8f54cdca91
--- /dev/null
+++ b/tests/ui/let_underscore_future.rs
@@ -0,0 +1,20 @@
+use std::future::Future;
+
+async fn some_async_fn() {}
+
+fn sync_side_effects() {}
+fn custom() -> impl Future<Output = ()> {
+    sync_side_effects();
+    async {}
+}
+
+fn do_something_to_future(future: &mut impl Future<Output = ()>) {}
+
+fn main() {
+    let _ = some_async_fn();
+    let _ = custom();
+
+    let mut future = some_async_fn();
+    do_something_to_future(&mut future);
+    let _ = future;
+}
diff --git a/tests/ui/let_underscore_future.stderr b/tests/ui/let_underscore_future.stderr
new file mode 100644
index 00000000000..f1b9b1d709e
--- /dev/null
+++ b/tests/ui/let_underscore_future.stderr
@@ -0,0 +1,27 @@
+error: non-binding let on a future
+  --> $DIR/let_underscore_future.rs:14:5
+   |
+LL |     let _ = some_async_fn();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider awaiting the future or dropping explicitly with `std::mem::drop`
+   = note: `-D clippy::let-underscore-future` implied by `-D warnings`
+
+error: non-binding let on a future
+  --> $DIR/let_underscore_future.rs:15:5
+   |
+LL |     let _ = custom();
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = help: consider awaiting the future or dropping explicitly with `std::mem::drop`
+
+error: non-binding let on a future
+  --> $DIR/let_underscore_future.rs:19:5
+   |
+LL |     let _ = future;
+   |     ^^^^^^^^^^^^^^^
+   |
+   = help: consider awaiting the future or dropping explicitly with `std::mem::drop`
+
+error: aborting due to 3 previous errors
+