Cannot initialize array of non-primitive type

[codemonkey85]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When trying to initialize a ReadOnlySpan of an enum, I'm hitting a runtime issue, "cannot initialize array of non-primitive type".

Expected Behavior

I should be able to initialize a ReadOnlySpan of an enum, based on this issue: dotnet/roslyn#61414

Steps To Reproduce

Here's a minimalistic solution with an example of the same code working in a console app, and crashing in a Blazor WASM app: https://github.com/codemonkey85/BlazorWasmIssueWithArrayInitializationWithRelevantPrimitives

The relevant code is:

ReadOnlySpan<MyEnum> myEnums = new[]
{
    MyEnum.A,
    MyEnum.B,
    MyEnum.C
};

Console.WriteLine(string.Join(", ", myEnums.ToArray()));

enum MyEnum
{
    A,
    B,
    C
}

Exceptions (if any)

crit: Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
      Unhandled exception rendering component: Cannot initialize array of non-primitive type (Parameter 'array')
System.ArgumentException: Cannot initialize array of non-primitive type (Parameter 'array')
   at System.Runtime.CompilerServices.RuntimeHelpers.GetSpanDataFrom(RuntimeFieldHandle fldHandle, RuntimeTypeHandle targetTypeHandle, Int32& count)
   at System.Runtime.CompilerServices.RuntimeHelpers.CreateSpan[MyEnum](RuntimeFieldHandle fldHandle)
   at DoesntWorkInBlazorWasm.wwwroot.Pages.Index.OnInitialized() in C:\git\BlazorWasmIssueWithArrayInitializationWithRelevantPrimitives\BlazorWasmIssueWithArrayInitializationWithRelevantPrimitives\wwwroot\Pages\Index.razor:line 22
   at Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync()

.NET Version

7.0.5

Anything else?

Please note, I do have .NET 8 preview 4 installed, but I am using .NET 7.0.5 (SDK 7.0.302) for this project.

PowerShell 7.3.4
PS C:\git\BlazorWasmIssueWithArrayInitializationWithRelevantPrimitives> dotnet --version
8.0.100-preview.4.23260.5
PS C:\git\BlazorWasmIssueWithArrayInitializationWithRelevantPrimitives> dotnet --info
.NET SDK:
 Version:   8.0.100-preview.4.23260.5
 Commit:    2268e7b15c

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.22621
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\8.0.100-preview.4.23260.5\

.NET workloads installed:
There are no installed workloads to display.

Host:
  Version:      8.0.0-preview.4.23259.5
  Architecture: x64
  Commit:       84a3d0e37e

.NET SDKs installed:
  7.0.302 [C:\Program Files\dotnet\sdk]
  7.0.400-preview.23225.8 [C:\Program Files\dotnet\sdk]
  8.0.100-preview.4.23260.5 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.16 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.0-preview.4.23260.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.16 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.0-preview.4.23259.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.16 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 7.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.0-preview.4.23260.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
  Not set

global.json file:
  Not found

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download

[stephentoub]

@lambdageek, could you take a look?

[lambdageek]

Works with the net8 runtime, fails with the net7 runtime
Tomorrow I'll try to find the PR that fixed it...

[codemonkey85]

@lambdageek Thanks for looking into this. Is there a possibility this can be fixed in an update to .NET 7?

[lambdageek]

Still haven't been able to track down why it is working in net8 and not in net7. The roslyn change dotnet/roslyn#61414 is complicating things...

[lambdageek]

Oh, I see. it's due to #81695 and #82093

Which both call mini_get_underlying_type on the type argument of the RuntimeHelpers.CreateSpan<T> call.

The non-intrinsic implementation doesn't have the underlying type logic. So (if it was possible to call ref-struct methods using reflection) calling CreateSpan indirectly will probably still assert in net8.

[lambdageek]

Ok, so this throws on net8 (and probably on net7):

using System.Reflection;

ReadOnlySpan<MyEnum> myEnums = new[]
{
    MyEnum.A,
    MyEnum.B,
    MyEnum.C
};

Console.WriteLine(string.Join(", ", myEnums.ToArray()));

var types = new Type[] {
        typeof(RuntimeFieldHandle),
        typeof(RuntimeTypeHandle),
        typeof(int).MakeByRefType(),
};
var mi = typeof(System.Runtime.CompilerServices.RuntimeHelpers).GetMethod("GetSpanDataFrom", BindingFlags.Static | BindingFlags.NonPublic, types);
Console.WriteLine (mi);

var pid = typeof(MyEnum).Assembly.GetType("<PrivateImplementationDetails>");
Console.WriteLine (pid);
var fis = pid.GetFields(BindingFlags.Static | BindingFlags.NonPublic);
var fi = fis[0];
Console.WriteLine (fi);

var parms = new object[] {
        fi.FieldHandle,
        typeof(MyEnum).TypeHandle,
        new int()
};
var result = mi.Invoke(null, parms);
Console.WriteLine (result);
Console.WriteLine (parms[2]);

enum MyEnum
{
    A,
    B,
    C
}

So now I can add a one-line fix for net 8 and backport to net7