Way too much (unhelpful) help is provided when mistakenly calling .borrow_mut() on a struct

[saethlin]

Given the following code: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=7da23c03f267a3483798d0615ee24563

fn main() {
    let t = Thing { x: 0, y: 0, z: 0 };
    *t.borrow_mut() = 1;
}

struct Thing {
    x: i32,
    y: i32,
    z: i32,
}

The current output is:

error[[E0599]](https://doc.rust-lang.org/nightly/error-index.html#E0599): no method named `borrow_mut` found for struct `Thing` in the current scope
 --> src/main.rs:3:8
  |
3 |     *t.borrow_mut() = 1;
  |        ^^^^^^^^^^ method not found in `Thing`
...
6 | struct Thing {
  | ------------ method `borrow_mut` not found for this struct
  |
  = help: items from traits can only be used if the trait is in scope
help: one of the expressions' fields has a method of the same name
  |
3 |     *t.x.borrow_mut() = 1;
  |        ++
help: one of the expressions' fields has a method of the same name
  |
3 |     *t.y.borrow_mut() = 1;
  |        ++
help: one of the expressions' fields has a method of the same name
  |
3 |     *t.z.borrow_mut() = 1;
  |        ++
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
  |
1 | [use std::borrow::BorrowMut;](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=7da23c03f267a3483798d0615ee24563#)
  |

For more information about this error, try `rustc --explain E0599`.
error: could not compile `playground` due to previous error

The output gets really out of control if you have a struct with 50 fields or so, which is what I'm currently looking at.

At the moment this only happens on nightly.

[compiler-errors]

ugh I added this. I can cut it down.

[saethlin]

FWIW, I was aiming for a field in the struct that is a RefCell. I just did struct.borrow_mut().field instead of struct.field.borrow_mut().

IMO the biggest problem with this suggestion at the moment is that it's suggesting that I call a method on a trait that's not in scope, when the RefCell method is, and that seems like the better suggestion to me. But maybe that's just bias from this particular scenario.

[compiler-errors]

IMO the biggest problem with this suggestion at the moment is that it's suggesting that I call a method on a trait that's not in scope

Yeah, I fixed that too. PR incoming.