Warn must_use in tuple

Author: sanxiyn

src/librustc_lint/unused.rs

@@ -162,6 +162,14 @@ impl LateLintPass for UnusedResults {
                         }
                     }
                 }
+                ty::TyTuple(ref tys) => {
+                    for &ty in tys {
+                        let result = check_must_use(cx, ty);
+                        if result.is_some() {
+                            return result;
+                        }
+                    }
+                }
                 _ => ()
             }
             None

src/test/compile-fail/unused-result.rs

@@ -45,4 +45,7 @@ fn main() {
     let _ = foo::<isize>();
     let _ = foo::<MustUse>();
     let _ = foo::<MustUseMsg>();
+
+    foo::<(MustUse, ())>(); //~ ERROR: unused result which must be used
+    foo::<(MustUseMsg, ())>(); //~ ERROR: unused result which must be used: some message
 }