Put #[diagnostic::on_move] on File

Author: mejrs

library/std/src/fs.rs

@@ -132,6 +132,7 @@ use crate::{error, fmt};
 /// [`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)]

tests/ui/diagnostic_namespace/on_move/std_impls.rs

@@ -0,0 +1,25 @@
+//@ dont-require-annotations: NOTE
+
+use std::fs::File;
+use std::sync::Arc;
+use std::rc::Rc;
+
+fn main(){
+    let file = File::open("foo.txt").unwrap();
+    (file, file);
+    //~^ ERROR use of moved value: `file`
+    //~| NOTE you can use `File::try_clone` to duplicate a `File` instance
+
+    let arc = Arc::new(42);
+    //~^ NOTE this move could be avoided by cloning the original `Arc`, which is inexpensive
+    (arc, arc);
+    //~^ ERROR the type `Arc` does not implement `Copy`
+    //~| NOTE consider using `Arc::clone`
+
+
+    let rc = Rc::new(12);
+    //~^ NOTE this move could be avoided by cloning the original `Rc`, which is inexpensive
+    (rc, rc);
+    //~^ ERROR the type `Rc` does not implement `Copy`
+    //~| NOTE consider using `Rc::clone`
+}

tests/ui/diagnostic_namespace/on_move/std_impls.stderr

@@ -0,0 +1,49 @@
+error[E0382]: use of moved value: `file`
+  --> $DIR/std_impls.rs:9:12
+   |
+LL |     let file = File::open("foo.txt").unwrap();
+   |         ---- move occurs because `file` has type `File`, which does not implement the `Copy` trait
+LL |     (file, file);
+   |      ----  ^^^^ value used here after move
+   |      |
+   |      value moved here
+   |
+   = note: you can use `File::try_clone` to duplicate a `File` instance
+
+error[E0382]: the type `Arc` does not implement `Copy`
+  --> $DIR/std_impls.rs:15:11
+   |
+LL |     let arc = Arc::new(42);
+   |         --- this move could be avoided by cloning the original `Arc`, which is inexpensive
+LL |
+LL |     (arc, arc);
+   |      ---  ^^^ value used here after move
+   |      |
+   |      value moved here
+   |
+   = note: consider using `Arc::clone`
+help: clone the value to increment its reference count
+   |
+LL |     (arc.clone(), arc);
+   |         ++++++++
+
+error[E0382]: the type `Rc` does not implement `Copy`
+  --> $DIR/std_impls.rs:22:10
+   |
+LL |     let rc = Rc::new(12);
+   |         -- this move could be avoided by cloning the original `Rc`, which is inexpensive
+LL |
+LL |     (rc, rc);
+   |      --  ^^ value used here after move
+   |      |
+   |      value moved here
+   |
+   = note: consider using `Rc::clone`
+help: clone the value to increment its reference count
+   |
+LL |     (rc.clone(), rc);
+   |        ++++++++
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0382`.