1 files changed, 39 insertions, 0 deletions
diff --git a/tests/ui/lint/unused/must_use-trait.rs b/tests/ui/lint/unused/must_use-trait.rs
new file mode 100644
index 000000000..0aa751443
--- /dev/null
+++ b/tests/ui/lint/unused/must_use-trait.rs
@@ -0,0 +1,39 @@
+#![deny(unused_must_use)]
+
+#[must_use]
+trait Critical {}
+
+trait NotSoCritical {}
+
+trait DecidedlyUnimportant {}
+
+struct Anon;
+
+impl Critical for Anon {}
+impl NotSoCritical for Anon {}
+impl DecidedlyUnimportant for Anon {}
+
+fn get_critical() -> impl NotSoCritical + Critical + DecidedlyUnimportant {
+    Anon {}
+}
+
+fn get_boxed_critical() -> Box<dyn Critical> {
+    Box::new(Anon {})
+}
+
+fn get_nested_boxed_critical() -> Box<Box<dyn Critical>> {
+    Box::new(Box::new(Anon {}))
+}
+
+fn get_critical_tuple() -> (u32, Box<dyn Critical>, impl Critical, ()) {
+    (0, get_boxed_critical(), get_critical(), ())
+}
+
+fn main() {
+    get_critical(); //~ ERROR unused implementer of `Critical` that must be used
+    get_boxed_critical(); //~ ERROR unused boxed `Critical` trait object that must be used
+    get_nested_boxed_critical();
+    //~^ ERROR unused boxed boxed `Critical` trait object that must be used
+    get_critical_tuple(); //~ ERROR unused boxed `Critical` trait object in tuple element 1
+    //~^ ERROR unused implementer of `Critical` in tuple element 2
+}