Casting hexadecimal int literals to f32 is necessary

[porky11]

Summary

Rust sadly doesn't support non-decimal floating point numbers.

Lint Name

clippy::unnecessary_cast

Reproducer

I tried this code:

-0x400 as f32

I saw this happen:

warning: casting integer literal to `f32` is unnecessary
  --> src/world/layer.rs:26:29
   |
26 |                 Vector::new(-0x400 as f32, 0x40 as f32),
   |                             ^^^^^^^^^^^^^ help: try: `-0x400_f32`

I expected to see this happen:

I expected it not to work anymore after following the hint, and that's what happened.

Version

rustc 1.64.0 (a55dd71d5 2022-09-19)
binary: rustc
commit-hash: a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52
commit-date: 2022-09-19
host: x86_64-unknown-linux-gnu
release: 1.64.0
LLVM version: 14.0.6

Additional Labels

No response

[kraktus]

@rustbot claim

[kraktus]

I'm unable to reproduce, it runs fine on playground (repro). Can you share a minimum reproducible example @porky11? Thanks

[porky11]

@kraktus

fn main() {
    println!("{}", -0x10 as f32);
}

It turns out the warning only appears when the hexadecimal number is negative.

[porky11]

@kraktus What even is your example?
Something seems wrong here. -0x400_f32 is of an opaque integer type, not of type f32.

Try this:

fn main() {
    let x: f32 = -0x400_f32;
    println!("{x}");
}

Is this a rust bug?

[porky11]

Now I get it: In hexadecimal, f32 is a digit. _ is allowed inside of numbers between digits as well.
So -0x400_f32 is the same as 0x400F32. Just a hexadecimal integer.

[kraktus]

Nice catch!