Put #[diagnostic::on_move] on File

library/std/src/fs.rs

@@ -132,6 +132,7 @@
 /// [`read`]: File::read
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "File")]
+#[diagnostic::on_move(note = "you can use `File::try_clone` to duplicate a `File` instance")]
 pub struct File {
     inner: fs_imp::File,
 }

library/std/src/lib.rs

@@ -278,6 +278,7 @@
 #![feature(const_trait_impl)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
+#![feature(diagnostic_on_move)]
 #![feature(doc_cfg)]
 #![feature(doc_masked)]
 #![feature(doc_notable_trait)]