Add more diagnostic items

library/std/src/error.rs

@@ -53,6 +53,7 @@ use crate::time;
 /// high-level module to provide its own errors while also revealing some of the
 /// implementation for debugging via `source` chains.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Error")]
 pub trait Error: Debug + Display {
     /// The lower-level source of this error, if any.
     ///