Using FastScriptReload causes Burst Jobs not to be compiled

[julhe]

I noticed that after we upgraded our project from Unity 2022.3. to Unity 6.4, our Burst jobs would stop being compiled as Burst Jobs and would use their managed fallback.

Apparently, FastScriptReload causes the (default) async burst compiler to soft-lock. This gets especially prominent, if Burst's Synchronous Compilation is active, which causes Unity to get stuck in an endless "Importing Assets" loop. This seems also to be easily reproducible with :

1. Create a new Unity 6.4 Project
2. Install FastScriptReload via Git/PackageManager
3. Create a simple Burst Job and save the file to something like BurstTest.cs

using Unity.Burst;
using Unity.Jobs;
using UnityEngine;

public class BurstTest : MonoBehaviour
{

    void Start()
    {
        BurstTestJob job = new ()
        {
            a = 1,
            b = 2
        };
        job.Schedule().Complete();
    }
}

[BurstCompile(CompileSynchronously = true)]
public struct BurstTestJob : IJob{
    public float a, b;
    public void Execute()
    {
        a *= b;
    }
}

4. Notice how Unity gets stuck importing.