unconditional_panic lint getting recognized in code that actually panics condtionally

[pro465]

I tried this code:

fn main() {
    let v: [i32; 0] = [];
    let _ = v.len() > 0 && v[0] == 0;
}

I expected to see this happen: code compiles and runs fine, without any error or panic

Instead, this happened:

error: this operation will panic at runtime
 --> t.rs:3:28
  |
3 |     let _ = v.len() > 0 && v[0] == 0;
  |                            ^^^^ index out of bounds: the length is 0 but the index is 0
  |
  = note: `#[deny(unconditional_panic)]` on by default

Meta

rustc --version --verbose:

rustc 1.56.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: armv7-linux-androideabi
release: 1.56.0
LLVM version: 13.0.0

[JanBeh]

Also note that this triggers the lint:

fn main() {
    let xs: [i32; 5] = [1, 2, 3, 4, 5];
    if false {
        println!("{}", xs[7]);
    }
}

(using rustc 1.63.0-nightly (43347397f 2022-06-23))

Example taken from URLO.

[JanBeh]

See also: #78803

[pro465]

@JanBeh thanks for the update! hopefully somebody will notice that issue and prepare a fix

[Noratrieb]

Closing in favor of #78803

[pro465]

@Nilstrieb , considering that this issue is still there in the latest nightly, even after #78803 was fixed, should we reopen this?

[fmease]

@rustbot label T-compiler A-lint A-control-flow A-const-prop

[ahqsoftwares]

There's something to note as well, it should be converted to a warning cuz the conditional part would never get called