Negation of unsigned literals lint does not fire when literal type is deduced

[netvl]

This leads to somewhat confusing results (see this SO question). Example code:

fn main() {
    let pair = (2953495866u, -2953495866);

    println!("Tell me about {}", pair);
    match pair {
        (x, y) if x == y => println!("These are twins"),
        (x, y) if x + y == 0 => println!("Antimatter, kaboom!"),
        (x, _) if x % 2 == 1 => println!("The first one is odd"),
        _ => println!("No correlation..."),
    }
}

Prints

Tell me about (2953495866, 18446744070756055750)
Antimatter, kaboom!

No compiler output is produced.

However, when u is added to the second literal:

fn main() {
    let pair = (2953495866u, -2953495866u);

    println!("Tell me about {}", pair);
    match pair {
        (x, y) if x == y => println!("These are twins"),
        (x, y) if x + y == 0 => println!("Antimatter, kaboom!"),
        (x, _) if x % 2 == 1 => println!("The first one is odd"),
        _ => println!("No correlation..."),
    }
}

A warning is printed by the compiler:

<anon>:3:30: 3:42 warning: negation of unsigned int literal may be unintentional, #[warn(unsigned_negate)] on by default
<anon>:3     let pair = (2953495866u, -2953495866u);
                                      ^~~~~~~~~~~~

[tomjakubowski]

Related I think: there is no warning when you provide a negative literal when indexing a Vec or something like it which implements Index<uint, _>. This is potentially confusing to those coming from languages where -1 is used to index the last element of a collection.

[kazagistar]

Just to help provide a minimal test case:

fn main() {
    let x: u32 = -10; -- no warning
    println!("{}", x);
}

Basically, the linter seems to only fire if there is a - and u in the same literal, but does not actually care about negative literals being assigned to and unsigned datatype.

[huonw]

Dupe of #5477.