Inconsistent reborrowing when accessing a struct fie... | rust-lang/rust

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When I assign a struct field of type &mut i32 to a variable, sometimes rust reborrows it for me, and sometimes it doesn't. This reborrowing should be done consistently or not at all.

In the below code, functions works1 and works2 compile fine, but fails1 through fails6 produce a compile error.

struct Thing<'a>(&'a mut i32);
impl Drop for Thing<'_> {
    fn drop(&mut self) {}
}

fn works1(t: Thing) {
    let mut _x = &mut 1;
    _x = t.0;
}

fn works2(t: Thing) {
    let mut _x: &mut i32;
    _x = t.0;
}

fn fails1(t: Thing) {
    let mut _x;
    _x = t.0;
}

fn fails2(t: Thing) {
    let mut _x = t.0;
}

fn fails3(t: Thing) {
    let Thing(mut _x) = t;
}

fn fails4(t: Thing) {
    let mut _x;
    Thing(_x) = t;
}

fn fails5(t: Thing) {
    let mut _x = &mut 1;
    Thing(_x) = t;
}

fn fails6(t: Thing) {
    let mut _x: &mut i32;
    Thing(_x) = t;
}

Error output

error[E0509]: cannot move out of type `Thing<'_>`, which implements the `Drop` trait
  --> src/lib.rs:18:10
   |
18 |     _x = t.0;
   |          ^^^
   |          |
   |          cannot move out of here
   |          move occurs because `t.0` has type `&mut i32`, which does not implement the `Copy` trait

error[E0509]: cannot move out of type `Thing<'_>`, which implements the `Drop` trait
  --> src/lib.rs:22:18
   |
22 |     let mut _x = t.0;
   |                  ^^^
   |                  |
   |                  cannot move out of here
   |                  move occurs because `t.0` has type `&mut i32`, which does not implement the `Copy` trait
   |
help: consider borrowing here
   |
22 |     let mut _x = &t.0;
   |                  +

error[E0509]: cannot move out of type `Thing<'_>`, which implements the `Drop` trait
  --> src/lib.rs:26:25
   |
26 |     let Thing(mut _x) = t;
   |               ------    ^ cannot move out of here
   |               |
   |               data moved here
   |               move occurs because `_x` has type `&mut i32`, which does not implement the `Copy` trait
   |
help: consider borrowing the pattern binding
   |
26 |     let Thing(ref mut _x) = t;
   |               +++

error[E0509]: cannot move out of type `Thing<'_>`, which implements the `Drop` trait
  --> src/lib.rs:31:17
   |
31 |     Thing(_x) = t;
   |           --    ^ cannot move out of here
   |           |
   |           data moved here
   |           move occurs because the place has type `&mut i32`, which does not implement the `Copy` trait
   |
help: consider borrowing the pattern binding
   |
31 |     Thing(ref _x) = t;
   |           +++

error[E0509]: cannot move out of type `Thing<'_>`, which implements the `Drop` trait
  --> src/lib.rs:36:17
   |
36 |     Thing(_x) = t;
   |           --    ^ cannot move out of here
   |           |
   |           data moved here
   |           move occurs because the place has type `&mut i32`, which does not implement the `Copy` trait
   |
help: consider borrowing the pattern binding
   |
36 |     Thing(ref _x) = t;
   |           +++

error[E0509]: cannot move out of type `Thing<'_>`, which implements the `Drop` trait
  --> src/lib.rs:41:17
   |
41 |     Thing(_x) = t;
   |           --    ^ cannot move out of here
   |           |
   |           data moved here
   |           move occurs because the place has type `&mut i32`, which does not implement the `Copy` trait
   |
help: consider borrowing the pattern binding
   |
41 |     Thing(ref _x) = t;
   |           +++

For more information about this error, try `rustc --explain E0509`.
error: could not compile `playground` (lib) due to 6 previous errors

Inconsistent reborrowing when accessing a struct field of type `&mut`.

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