Unused variables lint does not work inside an array length expression

[ecstatic-morse]

Array length expressions can can do anything that a const initializer can. However, the unused variables lint does not work inside an array length expression. For example,

fn main() {
    let _ = [(); {
        let x = 42;
        35
    }];
}

(Playground)

...compiles with no warnings:

   Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.51s
     Running `target/debug/playground`

[tesuji]

Seems like the liveness of x is over the ExitNode contains it, if I read the log correctly.
https://gist.github.com/lzutao/2053546ae057353af4f31cddc4676f58