PropertyGrid.SelectedObjects shows empty grid with typed arrays when PropertySort is NoSort (.NET 9/10 regression)

[p5ych08illy]

.NET version

10.0.100-preview (also affects .NET 9)

Did it work in .NET Framework?

Yes

Did it work in any of the earlier releases of .NET Core or .NET 5+?

Yes, worked correctly in .NET 8 and earlier.

Issue description

PropertyGrid.SelectedObjects silently fails (shows empty grid) when assigned a typed array (e.g., ItemTypeDescriptor[]) instead of object[] in multi-select scenarios. The internal ArrayTypeMismatchException is swallowed, making this bug difficult to diagnose.

The bug only occurs when PropertySort is set to NoSort.

Root cause: In MultiSelectRootGridEntry.GetMergedProperties(), the NoSort code path calls objects.AsSpan(1). However, Span<T> is not covariant - when AsSpan<object>() is called on an array whose runtime type is MyClass[] (not object[]), it throws ArrayTypeMismatchException.

// In MultiSelectRootGridEntry.GetMergedProperties():
if ((sort & PropertySort.Alphabetical) != 0)
{
    // This path does NOT use AsSpan - works fine
    commonProperties = GetCommonProperties(objects, presort: true, tab, parentEntry);
}
else
{
    // NoSort path - USES AsSpan - FAILS with typed arrays!
    properties = GetCommonProperties(objects.AsSpan(1), presort: true, tab, parentEntry);
    firstProperties = GetCommonProperties(objects.AsSpan(0, 1), presort: false, tab, parentEntry);
}

The root cause can be demonstrated standalone:

object[] arr = new MyClass[] { new MyClass() };  // Covariant assignment - compiles fine
arr.AsSpan();  // Throws ArrayTypeMismatchException!

Workaround: Use object[] explicitly instead of typed arrays:

// Instead of: var descriptors = new ItemTypeDescriptor[] { ... };
var descriptors = new object[] { new ItemTypeDescriptor(...), new ItemTypeDescriptor(...) };
propertyGrid.SelectedObjects = descriptors;

Steps to reproduce

1. Create a WinForms application targeting .NET 9 or .NET 10
2. Create a CustomTypeDescriptor-derived class (commonly used for property localization/filtering)
3. Set PropertyGrid.PropertySort = PropertySort.NoSort
4. Create a typed array of descriptors and assign to SelectedObjects
5. Observe: PropertyGrid is empty (no properties shown)
6. Change to object[] array - properties appear correctly

public class ItemTypeDescriptor : CustomTypeDescriptor
{
    private readonly WeakReference _component;
    public object? Component => _component.Target;

    public ItemTypeDescriptor(object component, ICustomTypeDescriptor parent)
        : base(parent)
    {
        _component = new WeakReference(component);
    }

    public override PropertyDescriptorCollection GetProperties()
        => base.GetProperties();

    public override object? GetPropertyOwner(PropertyDescriptor? pd) 
        => Component;
}

// Setup
propertyGrid.PropertySort = PropertySort.NoSort;

var model1 = new MyModel { Name = "Object1" };
var model2 = new MyModel { Name = "Object2" };

// BUG - typed array results in empty PropertyGrid:
var descriptors = new ItemTypeDescriptor[]
{
    new ItemTypeDescriptor(model1, TypeDescriptor.GetProvider(model1).GetTypeDescriptor(model1)!),
    new ItemTypeDescriptor(model2, TypeDescriptor.GetProvider(model2).GetTypeDescriptor(model2)!)
};
propertyGrid.SelectedObjects = descriptors;  // PropertyGrid shows empty!

// WORKAROUND - object[] works correctly:
var descriptors = new object[]
{
    new ItemTypeDescriptor(model1, TypeDescriptor.GetProvider(model1).GetTypeDescriptor(model1)!),
    new ItemTypeDescriptor(model2, TypeDescriptor.GetProvider(model2).GetTypeDescriptor(model2)!)
};
propertyGrid.SelectedObjects = descriptors;  // Properties are visible!

Minimal repro project attached.

PropertyGridSpanBug.zip

[SimonZhao888]

This problem may be caused by pr #10420