E0382: Add help for fixing a partially moved struct by manual assignment

Code

#[derive(Debug)]
struct A {
    a: String,
    b: String,
}


fn main(){
    let mut a: A = A { a: "test1".to_string(), b: "test2".to_string()};
    std::mem::drop(a.b);
    // A is now partially moved
    // a.b = "fix".to_string(); // fixing the partial move
    dbg!(a); // no error
}

Current output

error[E0382]: use of partially moved value: `a`
  --> src/main.rs:13:5
   |
10 |     std::mem::drop(a.b);
   |                    --- value partially moved here
...
13 |     dbg!(a); // no error
   |     ^^^^^^^ value used here after partial move
   |
   = note: partial move occurs because `a.b` has type `String`, which does not implement the `Copy` trait

Desired output

error[E0382]: use of partially moved value: `a`
  --> src/main.rs:13:5
   |
10 |     std::mem::drop(a.b);
   |                    --- value partially moved here
...
13 |     dbg!(a); // no error
   |     ^^^^^^^ value used here after partial move
   |
   = note: partial move occurs because `a.b` has type `String`, which does not implement the `Copy` trait
help: reassign a.b to a new value
12 |     a.b = String::default();
   |     ++++++++++++++++++++++++ assigning to a new value returns the struct to a useable state

Rationale and extra context

I was not aware for a long time this was possible. It is not explained in user-facing docs where it would be nice to have, and is often enough since often only the other fields are necessary, or the new owner returns a new value you could replace into this.

Its a more natural way of resolving this compared to using mem::replace before the value is moved.

Other cases

No response

Rust Version

rustc 1.80.1 (3f5fd8dd4 2024-08-06)
binary: rustc
commit-hash: 3f5fd8dd41153bc5fdca9427e9e05be2c767ba23
commit-date: 2024-08-06
host: x86_64-pc-windows-msvc
release: 1.80.1
LLVM version: 18.1.7

Anything else?

I'm not at all sure that "help:" is the correct way of phrasing this, as usually "help:" is used for cases where only one fix exists. Theres many ways to work around this, but i can't recall whether there is any existing phrasing for "have you considered this option?"

Start with the E0382 diagnostic described in the issue and reproduce the example from src/main.rs. Locate the compiler diagnostic implementation and its existing tests, then compare the current and desired output; done means the partially moved struct case receives the proposed reassignment guidance without regressing other E0382 diagnostics.