unused_variable: applying suggestion causes compiler error

[matthiaskrgr]

Given the following code:

fn main() {
    let res = { if true { return; } else { return; }; }; if res {}
}

The current output is:

warning: unreachable expression
 --> src/main.rs:2:58
  |
2 |     let res = { if true { return; } else { return; }; }; if res {}
  |                           ------                         ^^^^^^^^^ unreachable expression
  |                           |
  |                           any code following this expression is unreachable
  |
  = note: `#[warn(unreachable_code)]` on by default

warning: unused variable: `res`
 --> src/main.rs:2:9
  |
2 |     let res = { if true { return; } else { return; }; }; if res {}
  |         ^^^ help: if this is intentional, prefix it with an underscore: `_res`
  |

The problem is while the if res {} at the end is technically unreachable, it will still cause a compiler error if we auto-apply the let res = .. -> let _res = ... with cargo fix.

Could we somehow make the "remove if res {}" suggestion apply automatically so that it is performed before the res to _res rename?

[camsteffen]

Related: https://internals.rust-lang.org/t/should-dead-code-count-toward-var-liveness/16996

[ehuss]

I'm going to close as a duplicate of #104904.

[matthiaskrgr]

@ehuss this IS #104904 😅

[ehuss]

Sorry, copy/paste error. 😄 It should have been #107734.