Error when deserializing into &str slice in release mode

[george-lim]

Hey! I created a MRE for a bug I encountered below. This code compiles and works in debug mode, but in release the FooStr struct will not successfully deserialize.

use simd_json_derive::Deserialize;

#[derive(Deserialize)]
struct FooString {
    foo: String,
}

#[derive(Deserialize)]
struct FooStr<'de> {
    foo: &'de str,
}

fn main() {
    // This works fine in both debug and release mode (opt-level = 3)
    let mut json = br#"{"foo":"bar"}"#.to_vec();
    println!("{}", FooString::from_slice(&mut json).unwrap().foo);

    // This works fine in debug but fails in release mode (opt-level = 3)
    let mut json = br#"{"foo":"bar"}"#.to_vec();
    println!("{}", FooStr::from_slice(&mut json).unwrap().foo);
}

[Licenser]

Hi,

good catch! I added a test:

#[test]
fn foo_str() {
    #[derive(Deserialize)]
    struct FooStr<'de> {
        foo: &'de str,
    }
    let mut json = br#"{"foo":"bar"}"#.to_vec();
    let res = FooStr::from_slice(&mut json);
    assert!(res.is_ok());
    assert_eq!(res.unwrap().foo, "bar");
}

Clearly a bug, not a panic however, it returns a Err the panic comes from the unwrap() I'll rename the issue and see how quick I can fix it :)

[george-lim]

oh yeah whoops I wasn't paying attention when I wrote the MRE, just threw unwrap for convenience haha

[Licenser]

This is a really tricky one, I can reproduce it but I can't make sense of it so far

[george-lim]

Not sure if this helps, but I found out that the following works in release mode

#[derive(Deserialize)]
struct FooOptionStr<'de> {
    foo: Option<&'de str>,
}

[Licenser]

Okay, this took a lot of digging, but I found it. The use of MaybeUninit and .assume_init() was wrong and led to undefined behavior. This didn't pop up in the release code but optimisations lead to (I assume) freeing of memory that shouldn't have been freed.

The rewrite of the deserializer avoids MaybeUninit altogether in favour of Option's at the cost of some performance, but the code is free of unsafe and sound.

I'll release this as 0.12.0 along with an entry in the advisory-db to push people to update form 0.11 (or earlier) and yank affected versions from crates.io