Confusing error message with unimplemented Clone

[andreytkachenko]

Consider this example:

struct Test(u64, u64);
impl Test {
    fn into_tuple(self) -> (u64, u64) {
        (self.0, self.1)
    }
}
fn main() {
    let x = vec![Test(1,1), Test(1,2)];
    
    let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
}

struct Test is not implementing Clone trait, but here is the error message:

   Compiling playground v0.0.1 (file:///playground)
error[E0507]: cannot move out of borrowed content
  --> src/main.rs:12:39
   |
12 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ^^^^^^^^^^^^ cannot move out of borrowed content

error: aborting due to previous error

[estebank]

Proposed output:

error[E0507]: cannot move out of borrowed content
  --> src/main.rs:12:39
   |
1  | struct Test(u64, u64);
   | ---------------------- `Test` doesn't implement `Clone`
...
12 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ^^^^^^^^^^^^ cannot move out of borrowed content
   |
   = help: `test` is of type `&Test` and `Test` doesn't implement `Clone`, so you're cloning the borrow

error: aborting due to previous error

[estebank]

Triage, current output:

error[E0507]: cannot move out of a shared reference
  --> src/main.rs:10:39
   |
10 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ^^^^^^^^^^^^ move occurs because value has type `Test`, which does not implement the `Copy` trait

[estebank]

Current output:

error[E0507]: cannot move out of a shared reference
  --> src/main.rs:10:39
   |
10 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ^^^^^^^^^^^^^------------
   |                                       |            |
   |                                       |            value moved due to this method call
   |                                       move occurs because value has type `Test`, which does not implement the `Copy` trait
   |
note: `Test::into_tuple` takes ownership of the receiver `self`, which moves value
  --> src/main.rs:3:19
   |
3  |     fn into_tuple(self) -> (u64, u64) {
   |                   ^^^^

We should probably suggest #[derive(Copy)] on Test.

[estebank]

Output with #122603:

error[E0507]: cannot move out of a shared reference
  --> f109.rs:10:39
   |
10 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ^^^^^^^^^^^^ ------------ value moved due to this method call
   |                                       |
   |                                       move occurs because value has type `Test`, which does not implement the `Copy` trait
   |
note: `Test::into_tuple` takes ownership of the receiver `self`, which moves value
  --> f109.rs:3:19
   |
3  |     fn into_tuple(self) -> (u64, u64) {
   |                   ^^^^
note: if `Test` implemented `Clone`, you could clone the value
  --> f109.rs:1:1
   |
1  | struct Test(u64, u64);
   | ^^^^^^^^^^^

We could further explain that the .clone() is on the reference.

[estebank]

Current output:

error[E0507]: cannot move out of a shared reference
  --> src/main.rs:10:39
   |
10 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ^^^^^^^^^^^^ ------------ value moved due to this method call
   |                                       |
   |                                       move occurs because value has type `Test`, which does not implement the `Copy` trait
   |
note: `Test::into_tuple` takes ownership of the receiver `self`, which moves value
  --> src/main.rs:3:19
   |
3  |     fn into_tuple(self) -> (u64, u64) {
   |                   ^^^^
note: if `Test` implemented `Clone`, you could clone the value
  --> src/main.rs:1:1
   |
1  | struct Test(u64, u64);
   | ^^^^^^^^^^^ consider implementing `Clone` for this type
...
10 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ------------ you could clone this value

[andreytkachenko]

Now it produces better message:

   Compiling playground v0.0.1 (/playground)
error[E0507]: cannot move out of a shared reference
  --> src/main.rs:10:39
   |
10 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ^^^^^^^^^^^^ ------------ value moved due to this method call
   |                                       |
   |                                       move occurs because value has type `Test`, which does not implement the `Copy` trait
   |
note: `Test::into_tuple` takes ownership of the receiver `self`, which moves value
  --> src/main.rs:3:19
   |
3  |     fn into_tuple(self) -> (u64, u64) {
   |                   ^^^^
note: if `Test` implemented `Clone`, you could clone the value
  --> src/main.rs:1:1
   |
1  | struct Test(u64, u64);
   | ^^^^^^^^^^^ consider implementing `Clone` for this type
...
10 |     let _tuples = x.iter().map(|test| test.clone().into_tuple()).collect::<Vec<_>>();
   |                                       ------------ you could clone this value

For more information about this error, try `rustc --explain E0507`.