MethodInfo Invoke with [Optional] argument as Type.Missing fails

[jborean93]

Description

I'm trying to invoke a method that contains an OptionalAttribute without a default value set using reflection but it fails when using Type.Missing with

System.ArgumentException: Object of type 'System.Reflection.Missing' cannot be converted to type 'System.Int32'.

Reproduction Steps

using System;
using System.Runtime.InteropServices;

public class Program
{
    public static void Main()
    {
        int value1 = (int)typeof(Program).GetMethod(nameof(TestMethod1))
            .Invoke(null, new[] { Type.Missing });
        Console.WriteLine($"TestMethod1() => {value1}");

        int value2 = (int)typeof(Program).GetMethod(nameof(TestMethod2))
            .Invoke(null, new[] { Type.Missing });
        Console.WriteLine($"TestMethod2() => {value2}");

        int value3 = (int)typeof(Program).GetMethod(nameof(TestMethod3))
            .Invoke(null, new[] { Type.Missing });
        Console.WriteLine($"TestMethod3() => {value3}");
    }

    public static int TestMethod1(int value = 1) => value;
    public static int TestMethod2([Optional, DefaultParameterValue(1)] int value) => value;
    public static int TestMethod3([Optional] int value) => value;
}

Expected behavior

TestMethod1() => 1
TestMethod2() => 1
TestMethod3() => 0

Actual behavior

TestMethod1() => 1
TestMethod2() => 1
Unhandled exception. System.ArgumentException: Object of type 'System.Reflection.Missing' cannot be converted to type 'System.Int32'.
   at System.RuntimeType.CheckValue(Object& value, Binder binder, CultureInfo culture, BindingFlags invokeAttr)
   at System.Reflection.MethodBaseInvoker.InvokeWithOneArg(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Program.Main() in /home/user/dev/Example/Program.cs:line 16

Regression?

It does not look like it, the same example fails on .NET Framework 4.8.

Known Workarounds

The workaround is to pass in null (I'm not sure if that works in all scenarios or not).

int value3 = (int)typeof(Program).GetMethod(nameof(TestMethod3))
            .Invoke(null, new object[] { null });

Configuration

net8.0
All OS
Tested on x64
I don't believe this is specific to this configuration.

Other information

This is opened in response to PowerShell/PowerShell#21372. PowerShell is using an ExpressionTree to invoke the method. It uses the ParameterInfo.DefaultValue for arguments not specified in PowerShell which for TestMethod3() is Missing.

Add-Type -TypeDefinition @'
using System;
using System.Runtime.InteropServices;

public class MyClass
{
    public static int TestMethod1(int value = 1) => value;
    public static int TestMethod2([Optional, DefaultParameterValue(1)] int value) => value;
    public static int TestMethod3([Optional] int value) => value;
}
'@

[MyClass].GetMethod('TestMethod1').GetParameters() | Select-Object Attributes, DefaultValue

          Attributes DefaultValue
          ---------- ------------
Optional, HasDefault            1

[MyClass].GetMethod('TestMethod2').GetParameters() | Select-Object Attributes, DefaultValue

          Attributes DefaultValue
          ---------- ------------
Optional, HasDefault            1

[MyClass].GetMethod('TestMethod3').GetParameters() | Select-Object Attributes, DefaultValue

Attributes DefaultValue
---------- ------------
  Optional System.Reflection.Missing

I've got a patch for PowerShell that uses Expression.Default(parameters[0].ParameterType); which solves this issue but it seems like this might be a bug in .NET that should be fixed here. If not it would be great to understand more about why the current behaviour fails and if there are other cases were ParameterInfo.DefaultType might also be System.Reflection.Missing.

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[steveharter]

This is by design; see the test Invoke_OptionalParameterUnassingableFromMissing_WithMissingValue_ThrowsArgumentException. where the parameter type is string. The similar test before that has an object parameter type and doesn't throw but the incoming value is Type.Missing which can be passed as object.

Also verified previous versions (v7, v8) are consistent.

[jborean93]

Thanks @steveharter for replying, so is the solution here to just provide null for these values explicitly? Are you aware of any other scenario where ParameterInfo.DefaultValue might also by System.Reflection.Missing that could potential cause problems if I change the PowerShell code to provide the default value/null for this argument when calling it?

[jborean93]

Oh and the linked issue for that test seems to be unrelated mono/mono#15025 so not sure what the reason behind this behaviour is.