dotnet/roslyn

CLR bug with static variable in struct could be warned by the compiler

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#10,126 opened on Mar 26, 2016

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 (27 comments) (2 reactions) (0 assignees)C# (20,414 stars) (4,257 forks)batch import
Area-CompilersFeature - Warning WavesFeature Requesthelp wanted

Description

The following code compiles, but throws a TypeLoadException when executed.

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var x = MyStruct.Empty;
        }

        public struct MyStruct
        {
            public static readonly MyStruct? Empty = null;
        }
    }
}

Since Empty is static, this is not a cyclic struct layout issue. It would be nice if the compiler produced warnings that tells you that you are likely to run into this CLR bug at runtime

[Note from @gafter this is due to CLR bug https://github.com/dotnet/coreclr/issues/4049. See also https://github.com/dotnet/coreclr/issues/7957 and https://github.com/dotnet/coreclr/issues/22553 for other situations where the warning would be helpful]

Contributor guide

Tech stack
csharp
Domain
developer experience
Issue type
feature
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.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C#Roslyn compiler basicsDiagnostic infrastructure
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Investigate the referenced CLR bugs (dotnet/coreclr#4049, #7957, #22553) to understand the specific conditions causing TypeLoadException. Study Roslyn's existing warning implementation patterns in the compiler, such as how warnings are defined in ErrorCode.cs and DiagnosticDescriptors. Focus on the semantic analysis of struct types to detect nullable static fields in value types. Propose a new warning ID and implement the detection logic in the appropriate diagnostic analyzer.