Fatal error in side_effect_utils.ml

[franziskuskiefer]

The following code fails to extract to F*.

enum A{
    X
}
enum B{
    X
}
trait Rng {}

fn other_fun<R: Rng>(rng: &mut R) -> Result<(A, B), u8> {
    Ok((A::X, B::X))
}

fn fun<R: Rng>(x: u8, rng: &mut R) -> Result<(A, B), u8> {
    return Ok((A::X, other_fun(rng)?.1));
}

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This can be worked around with the following

fn fun<R: Rng>(x: u8, rng: &mut R) -> Result<(A, B), u8> {
    let tmp = other_fun(rng)?;
    return Ok((A::X, tmp.1));
}

[maximebuyse]

I quickly investigated. The reproducer can be minimized to the following:

fn other_fun(rng: &mut i8) -> Result<(), ()> {
    Ok(())
}

fn fun(rng: &mut i8) -> Result<(), ()> {
    return Ok(other_fun(rng)?);
}

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I used a modified hax version to pretty-print the expected types in the error, which gives:
Expected two exact same types, got x=core::result::t_Result<tuple0, tuple0> and y=tuple2<int, core::result::t_Result<tuple0, tuple0>>

So it seems like there is a conflict between hoisting the ? side effect and hoisting the function call that should return the value of its &mut parameter.