dotnet/runtime

Reflection on enums creates instances of open generic types

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#7,976 opened on Apr 28, 2017

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area-System.Reflectionbughelp wanted

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Description

From https://codeblog.jonskeet.uk/2017/04/26/surprise-creating-an-instance-of-an-open-generic-type/

using System;
using System.Reflection;
 
class Program
{
    static void Main(string[] args)
    {
        object x = GetWeirdValue();
        // This line prints True
        Console.WriteLine(x.GetType().GetTypeInfo().IsGenericTypeDefinition);
    }
 
    static object GetWeirdValue() =>
        typeof(Generic<>.GenericEnum).GetTypeInfo()
            .GetDeclaredField("Foo")
            .GetValue(null);
 
    class Generic<T>
    {
        public enum GenericEnum
        {
            Foo = 0
        }
    }
}

Contributor guide

Research direction
Inspect the use of reflection on nested enums and trace the internal handling of generic type definitions to understand why an instance of an open generic type is created.
Tech stack
csharp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#Reflection
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40