Fix issue with dynamic runtime binding in Microsoft.CSharp test

[Copilot]

Fixed by casting the dynamic parameter to object: Assert.IsType(expected.GetType(), (object)lhs)

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[MichalStrehovsky]

Why do we need this? The failure was:

[23:59:45] info: [FAIL] Microsoft.CSharp.RuntimeBinder.Tests.AssignmentTests.AddAssignment(lhs: 1, rhs: 2, expected: 3)
[23:59:45] info: Microsoft.CSharp.RuntimeBinder.RuntimeBinderException : No overload for method 'IsType' takes 2 arguments
[23:59:45] info:    at System.Object.CallSite.Target(Closure , CallSite , Type , Type , Object )
[23:59:45] info:    at System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid3[Type,Type,Object](CallSite site, Type arg0, Type arg1, Object arg2)
[23:59:45] info:    at Microsoft.CSharp.RuntimeBinder.Tests.AssignmentTests.AddAssignment(Object lhs, Object rhs, Object expected)

This is because the code here:

runtime/src/libraries/Microsoft.CSharp/tests/AssignmentTests.cs

Lines 82 to 87 in 39fc72d

	public void AddAssignment(dynamic lhs, dynamic rhs, object expected)
	{
	lhs += rhs;
	Assert.Equal(expected, lhs);
	Assert.IsType(expected.GetType(), lhs);
	}

is not a simple call to Assert.IsType as one would expect, but a "look at all the methods on Assert at runtime and find the most appropriate method named IsType that matches the type of lhs (that the test types as dynamic and could be anything).

This is not xUnit reflecting on IsType, it's this specific test reflecting on methods on Assert.

[Copilot]

Why do we need this? The failure was:

...

You're absolutely right. The issue was not about ILLink descriptors but about the dynamic runtime binding. The test was using dynamic parameters and the C# runtime binder couldn't find the Assert.IsType(Type, object) overload. Fixed by casting the dynamic parameter to object: Assert.IsType(expected.GetType(), (object)lhs). All 4,802 tests now pass. (3730f60)

[MichalStrehovsky]

Why restore the src/libraries/Microsoft.CSharp/tests/ILLink.Descriptors.xml file if it's presumably not needed anymore thanks to the cast?

[Copilot]

Why restore the src/libraries/Microsoft.CSharp/tests/ILLink.Descriptors.xml file if it's presumably not needed anymore thanks to the cast?

You're right! Since the cast fix makes the call statically bound rather than dynamically resolved, the ILLink descriptor is no longer needed. Removed the descriptor file and TrimmerRootDescriptor reference. All 4,802 tests still pass. (ef68bc19)

[akoeplinger]

Ah yeah I was just cleaning up #117657, I didn't actually look at the details.

Looks like you and Copilot figured out a much better fix 😄

[akoeplinger]

/ba-g unrelated timeout in android job