False-positive unused variable warning in the presence of unimplemented!()

[nzentzis]

Given the following code: Playground

pub enum View {
    A, B
}

pub struct Foo;

impl Foo {
    pub fn do_stuff(&self, view: View) {
        let _: f32 = unimplemented!();
        match view {
            _ => {},
        }
    }
}

The current output warns about an unused parameter:

warning: unused variable: `view`
 --> src/lib.rs:8:28
  |
8 |     pub fn do_stuff(&self, view: View) {
  |                            ^^^^ help: if this is intentional, prefix it with an underscore: `_view`
  |
  = note: `#[warn(unused_variables)]` on by default

However, the view parameter is used in the match block, even though it'll never be executed as things stand. If I comment out the unimplemented!(), the warning goes away.

[ghost]

I thought this was intended behavior? The variable really is never used when the codes runs...

[ehuss]

Thanks for the report! This is intended behavior, as the variables really aren't used since the "used" parts are in an unreachable block. Closing as a duplicate of #78136.