Compiler incorrectly understand initialisation of vars with patterns.

[lovely-error]

Hey, this code does not work in 1.68.2, but it should.

struct W(u8);

fn sooqa () -> Option<W> {
    Some(W(0))
}

fn main() {
    let p@W(v);
    loop {
        if let Some(p_) = sooqa() { p = p_;break /*A*/ };
    }
    println!("{}", v);
}

This is the error message

error[[E0381]](https://doc.rust-lang.org/stable/error_codes/E0381.html): used binding `v` isn't initialized
  --> src/main.rs:13:20
   |
9  |     let p@W(v);
   |             - binding declared here but left uninitialized
...
13 |     println!("{}", v);
   |                    ^ `v` used here but it isn't initialized
   |
   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider assigning a value
   |
9  |     let p@W(v = 0);
   |               +++

[fmease]

Hmm, interesting code 😅 These two simplified snippets don't compile either for the same reason:

struct W(u8);

fn main() {
    let p@W(v);
    v = 10;
    p;
}

stderr (also with a butchered suggestion diagnostic)

error[E0381]: used binding `p` isn't initialized
 --> src/main.rs:6:5
  |
4 |     let p@W(v);
  |         - binding declared here but left uninitialized
5 |     v = 10;
6 |     p;
  |     ^ `p` used here but it isn't initialized
  |
help: consider assigning a value
  |
4 |     let p = todo!()@W(v);
  |           +++++++++

struct W(u8);

fn main() {
    let p@W(v);
    p = W(10);
    v;
}

stderr (same butchered suggestion as in the PR description)

error[E0381]: used binding `v` isn't initialized
 --> src/main.rs:6:5
  |
4 |     let p@W(v);
  |             - binding declared here but left uninitialized
5 |     p = W(10);
6 |     v;
  |     ^ `v` used here but it isn't initialized
  |
help: consider assigning a value
  |
4 |     let p@W(v = 0);
  |               +++