Unnecessarily duplicated delegate types

[nihohit]

Type aliases for passed callbacks are ignored, and each function gets its own callback, even if the rust file contains information that shows.

temp.rs:

pub type SingleIntCallback = extern "C" fn(param: i32);

#[no_mangle]
pub unsafe extern "C" fn first(_callback: SingleIntCallback) {}

#[no_mangle]
pub unsafe extern "C" fn second(_callback: SingleIntCallback) {}

build.rs::

csbindgen::Builder::default()
    .input_extern_file("src/temp.rs")
    .csharp_dll_name("example")
    .always_included_types(["SingleIntCallback"])
    .csharp_use_function_pointer(false)
    .generate_csharp_file("../unity/Runtime/NativeMethods.cs")
    .unwrap()

Output:

// <auto-generated>
// This code is generated by csbindgen.
// DON'T CHANGE THIS DIRECTLY.
// </auto-generated>
#pragma warning disable CS8500
#pragma warning disable CS8981
using System;
using System.Runtime.InteropServices;


namespace CsBindgen
{
    internal static unsafe partial class NativeMethods
    {
        const string __DllName = "example";



        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        internal delegate void first__callback_delegate(int param);

        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        internal delegate void second__callback_delegate(int param);



        [DllImport(__DllName, EntryPoint = "first", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
        internal static extern void first(first__callback_delegate _callback);

        [DllImport(__DllName, EntryPoint = "second", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
        internal static extern void second(second__callback_delegate _callback);


    }



}

This requires in Unity:

    [AOT.MonoPInvokeCallback(typeof(first__callback_delegate))]
    [AOT.MonoPInvokeCallback(typeof(second__callback_delegate))]

Which easily explodes with the number of generated functions.

I'd be happy to fix this, but I don't know the structure of this project, so I'll appreciate pointers on where to look.