`match_single_binding` suggestion introduced an extra semicolon

[jruderman]

Summary

Following the suggestion of match_single_binding would put two semicolons after a statement.

This is wrong-ish (it would cause rustc to emit "warning: unnecessary trailing semicolon").

Reproducer

I tried clippy_driver on this code:

fn _f(r: Option<u32>) {
    let _t = match r {
        x => {
            match x {
                Some(_) => { println!("Some"); },
                None => { println!("None"); }
            }
        },
    };
}

fn main(){}

I got:

warning: this let-binding has unit value
 --> ulm.rs:2:5
  |
2 | /     let _t = match r {
3 | |         x => {
4 | |             match x {
5 | |                 Some(_) => { println!("Some"); },
... |
8 | |         },
9 | |     };
  | |______^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_unit_value
  = note: `#[warn(clippy::let_unit_value)]` on by default
help: omit the `let` binding
  |
2 ~     match r {
3 +         x => {
4 +             match x {
5 +                 Some(_) => { println!("Some"); },
6 +                 None => { println!("None"); }
7 +             }
8 +         },
9 +     };
  |

warning: this match could be written as a `let` statement
 --> ulm.rs:2:5
  |
2 | /     let _t = match r {
3 | |         x => {
4 | |             match x {
5 | |                 Some(_) => { println!("Some"); },
... |
8 | |         },
9 | |     };
  | |______^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#match_single_binding
  = note: `#[warn(clippy::match_single_binding)]` on by default
help: consider using a `let` statement
  |
2 ~     let x = r;
3 +     let _t = match x {
4 +         Some(_) => { println!("Some"); },
5 +         None => { println!("None"); }
6 +     };;
  |

warning: 2 warnings emitted

In the final suggestion, the final semicolon should be removed.

Version

rustc 1.66.0-nightly (bed4ad65b 2022-10-25)
binary: rustc
commit-hash: bed4ad65bf7a1cef39e3d66b3670189581b3b073
commit-date: 2022-10-25
host: x86_64-apple-darwin
release: 1.66.0-nightly
LLVM version: 15.0.2

Additional Labels

No response

[alex-semenyuk]

@rustbot claim