Add test for #[deprecated] attribute on trait impl block.

src/test/ui/deprecation/deprecation-sanity.rs

@@ -30,4 +30,13 @@ fn multiple1() { }
 #[deprecated(since = "a", since = "b", note = "c")] //~ ERROR multiple 'since' items
 fn f1() { }
 
+struct X;
+
+#[deprecated = "hello"] //~ ERROR this `#[deprecated]' annotation has no effect
+impl Default for X {
+    fn default() -> Self {
+        X
+    }
+}
+
 fn main() { }

src/test/ui/deprecation/deprecation-sanity.stderr

@@ -58,7 +58,15 @@ error[E0538]: multiple 'since' items
 LL | #[deprecated(since = "a", since = "b", note = "c")]
    |                           ^^^^^^^^^^^
 
-error: aborting due to 9 previous errors
+error: this `#[deprecated]' annotation has no effect
+  --> $DIR/deprecation-sanity.rs:35:1
+   |
+LL | #[deprecated = "hello"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^ help: try removing the deprecation attribute
+   |
+   = note: `#[deny(useless_deprecated)]` on by default
+
+error: aborting due to 10 previous errors
 
 Some errors have detailed explanations: E0538, E0541, E0550, E0551, E0565.
 For more information about an error, try `rustc --explain E0538`.