Debugger display of compiled lambda shows "Internal Error evaluating expression"

[AaronHerchmer]

Hi,

I'm trying to compile a Func delegate from an expression for filtering a collection in .NET Core 3.1 and after calling .Compile() on the expression the value of the delegate is:

{Method = \<Internal Error evaluating expression>}

When I run the exact same code in a .NET 4.7.2 console application, it works, and I am able to filter a collection using that delegate.

var expressionParameter = Expression.Parameter(typeof(DateTime), "x");
var expressionProperty = Expression.Property(expressionParameter, "Date");

var expressionValue = Expression.Constant(new DateTime(2020, 03, 10), typeof(DateTime));
var compareExpression = Expression.GreaterThanOrEqual(expressionProperty, expressionValue);

var lambdaExpression = Expression.Lambda<Func<DateTime,bool>>(compareExpression, expressionParameter);
var testCompile = lambdaExpression.Compile();

[GrabYourPitchforks]

Can you clarify your issue? Is is that you're seeing a problem with the VS debugger specifically, or is the application failing at runtime?

[AaronHerchmer]

I'm just seeing the result in the VS debugger, the value of the variable testCompile is {Method = \<Internal Error evaluating expression>} in .NET Core, and an appropriate Func in 4.7.2.

[stephentoub]

But does testCompile still work? The question is if the concern is just around debugging or if it's actually affecting behavior at run-time.

[AaronHerchmer]

Ya sorry it still returns the delegate properly just the value of the display inside the debugger is incorrect. The delegate still works at runtime.

[theCuriousOne]

I am experiencing the same error. We have just upgraded our code from .net core 2.1 to 3.1 and while in 2.1 I see no such error in 3.1 it shows:

{Method = <Internal Error evaluating expression>}

I also have a failing test that I am trying to debug, and now I am not sure if something have changed in the Expressions between versions 2.1 and 3.1 or it is an debugger issue and I am looking in the wrong place.

[sidney-pauly]

I had a similar issue to @theCuriousOne. I detailed my solution/bug-report here: #35336

[theCuriousOne]

I had a similar issue to @theCuriousOne. I detailed my solution/bug-report here: https://github.com/dotnet/runtime/issues/35336

@sidney-pauly your url is incorrect https://github.com/dotnet/runtime/issues/35336 it should be placed in both brackets -> in [] is for text that you see, and in () is the link behind the text.

[cston]

{Method = \}

The delegate is a dynamic method which is not viewable in the debugger.

[theCuriousOne]

@cston The same code was viewable in VisualStudio 2017, but not in VisualStudio 2019. The question is: what change in the debugger caused this? Was the VS2017 version wrong or did it handled it better?

[CzBuCHi]

got same error but i managed to find workaround:

instead of having delegate in watch use delegate.Method - then debugger shows correct method info

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PS: yea i know this post is 2 years old ...