No warning for open range loop

[jamesmunns]

Code

fn main() {
    for idx in 0u8.. {
        println!("{:02X}", idx);
    }
    // not unreachable!
    func();
}

// no `clippy::infinite_loop` lint!
fn func() {
    for idx in 0u8.. {
        println!("{:02X}", idx);
    }
}

Current output

(loops forever in release, or panics in debug, no warning)

Desired output

Some kind of warning that `for i in (0..)` will loop forever

Rationale and extra context

I was surprised to learn today that iterating over a RangeFrom will wrap (or panic on overflow in debug). RangeFrom's docs (https://doc.rust-lang.org/std/ops/struct.RangeFrom.html#impl-Iterator-for-RangeFrom%3CA%3E) do note this, but it was still surprising to me.

It might be worth linting on this in some form, either in rustc or clippy, neither of which have anything to say about this construct.

Other cases

Rust Version

All versions (I guess since 1.6 where RangeFrom stabilized?)

Anything else?

Edit: This is definitely working as designed/as specified, and I did find some older issues, as well as discussions for "new ranges" that cover this point. I still think it might be worth emitting a diagnostic/lint for this because it may be surprising/unexpected for other people as well.

My code was fixed by switching to for idx in 0u32..=u32::MAX, which is what I really meant, and might be what we point people to in the diagnostic.

[okaneco]

Some discussion here rust-lang/libs-team#304

It doesn't look like anyone filed a suggestion for this to be added to clippy