GenAPI does not handle fixed buffers

[DaZombieKiller]

• This issue is blocking
• This issue is causing unreasonable pain

When using GenAPI on an assembly that contains fixed buffers, it will output the generated fixed buffer structures with unspeakable names, rather than fixed fields.

Given the following type:

public struct MyFixedBuffer
{
    public unsafe fixed int Buffer[64];
}

GenAPI will produce this output:

[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
public partial struct MyFixedBuffer
{
    public MyFixedBuffer.<Buffer>e__FixedBuffer Buffer;
    [System.Runtime.CompilerServices.CompilerGeneratedAttribute]
    [System.Runtime.CompilerServices.UnsafeValueTypeAttribute]
    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential, Size=256)]
    public partial struct <Buffer>e__FixedBuffer
    {
        public int FixedElementField;
    }
}

[ViktorHofer]

cc @safern @ericstj

[safern]

The reason why this is happening is because we don't have support to understand the fixed buffer metadata. It seems like we have never exposed a fixed buffer API in dotnet/runtime.

It seems like the compiler generates this into the IL

[StructLayout(LayoutKind.Sequential, Size = 256)]
    [CompilerGenerated]
    [UnsafeValueType]
    public struct <fixedBuffer>e__FixedBuffer
    {
        public char FixedElementField;
    }

    [FixedBuffer(typeof(char), 128)]
    public <fixedBuffer>e__FixedBuffer fixedBuffer;

and that is just what we preserve, rather than ignoring the CompilerGenerated struct and reading the FixedBuffer attribute to get the underlying type and length and translate it to the actual syntax.

Maybe we should consider supporting this in the new API Compat.

[MattGal]

[Triage]: Tossing into "Work tracking by/for other teams" epic ; GenAPI is primarily a runtime tool and the right folks are on the issue.

[DaZombieKiller]

and that is just what we preserve, rather than ignoring the CompilerGenerated struct and reading the FixedBuffer attribute to get the underlying type and length and translate it to the actual syntax.

I should note that the [FixedBuffer] attribute doesn't seem to be preserved in the current output, oddly. At least, it didn't seem to be in the few cases I tested with (all of which were similar to the example in the OP.)

[DaZombieKiller]

Should this be transferred to dotnet/sdk since that is now where GenAPI lives? The issue appears to still exist there.