net6.0-ios: AOT compiler fail when UnmanagedCallersOnly has CallConvs

[ericsink]

Description

We have a case where including CallConvs in an UnmanagedCallersOnly attribute causes the AOT compiler to fail.

This works:

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

public static class foo
{
        [UnmanagedCallersOnly]
        public static void fun(IntPtr p, int t)
        {
        }
}

but this one fails:

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

public static class foo
{
        [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvCdecl) })]
        public static void fun(IntPtr p, int t)
        {
        }
}

with this error:

eric@Erics-MacBook-Pro test % dotnet build
MSBuild version 17.3.0+92e077650 for .NET
  Determining projects to restore...
  Restored /Users/eric/Downloads/test/test.csproj (in 125 ms).
  Detected signing identity: (omitted)

  test -> /Users/eric/Downloads/test/bin/Debug/net6.0-ios/ios-arm64/test.dll
  Optimizing assemblies for size, which may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  Tool /usr/local/share/dotnet/packs/Microsoft.NETCore.App.Runtime.AOT.osx-x64.Cross.ios-arm64/6.0.8/Sdk/../tools/mono-aot-cross execution finished (exit code = 134).

/usr/local/share/dotnet/packs/Microsoft.iOS.Sdk/15.4.447/targets/Xamarin.Shared.Sdk.targets(1000,3): error : Failed to AOT compile test.dll, the AOT compiler exited with code 134 [/Users/eric/Downloads/test/test.csproj]

Build FAILED.

Reproduction Steps

issue516_repro.zip

Expected behavior

The build should succeed

Actual behavior

The AOT compiler fails with error code 134.

Regression?

No response

Known Workarounds

No response

Configuration

eric@Erics-MacBook-Pro test % dotnet --version
6.0.400

Other information

Originally found:

ericsink/SQLitePCL.raw#516

[SamMonoRT]

@ivanpovazan suggested this was fixed by #69759 for .NET 7.0 - We don't intend to backport to 6.0. Marking issue as 8.0 for validation

[ivanpovazan]

cc @LeVladIonescu

[LeVladIonescu]

Validated fixes from #69759 using the following dotnet versions:

• 8.0.100-alpha.1.22567.28
• 7.0.100-rc.1.22431.12

AOT compilation passes for CallConvs included in an UnmanagedCallersOnly attribute.