Number loses precision on f32s

[Gelbpunkt]

Hi there, I've gone through a couple of issues but haven't found anything that quite matches my problem, so if this is a duplicate, feel free to close this and direct me elsewhere :)

The following small snippet replicates my issue:

use serde::{Deserialize, Serialize};
use serde_json;

#[derive(Deserialize, Serialize, Debug, Clone)]
struct Test(f32);

fn main() {
    let a = Test(5.55);
    let value = serde_json::to_value(a.clone()).unwrap();
    println!("{value:?}");
    let serialized = serde_json::to_string(&value).unwrap();
    println!("{serialized}");
    let serialized = serde_json::to_string(&a).unwrap();
    println!("{serialized}");
}

// Number(5.550000190734863)
// 5.550000190734863
// 5.55

I would expect the serialized values to be identical (and serialized to 5.55), but they aren't. This happens both with and without arbitrary_precision and float_roundtrip enabled. I would've expected this to be precisely 5.55, especially with arbitrary_precision enabled. When changing the type to an f64, it works as expected.

[dtolnay]

Good catch, this is a bug.