"&mut v[v[0]..]" doesn't compile

[safinaskar]

Consider this code:

fn main() {
    let mut v = vec![1, 2];
    let x = &mut v[v[0]..];
}

It doesn't compile ( https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=b69d691f31f8c8ef9e7ca949c4be542b, rustc 1.68.2).

Of course, this example can be simply fixed by extracting v[0]. But I still argue that this is correct code, and it should compile. Even if this is not possible to fix in short time, I still think this should be fixed in some next-generation borrow checker.

I actually got similar code in my actual production code base. This is simplified example from my production code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=e56a648d80a8af7c3eabdcfe504df774

Adding -Zpolonius changes nothing

[safinaskar]

@rustbot label +A-lifetimes +T-compiler +A-borrow-checker +NLL-polonius +A-NLL

[safinaskar]

Even &mut v[(v.len() - 3)..] doesn't compile!

[csmoe]

Duplicate of #30127

[safinaskar]

Indeed. v.index_mut(v[0]..) works