CA1003 does not take the return value of an event handler into account

[dlebansais]

Version Used: 17.10.0

Steps to Reproduce:

1. Create a .NET 8 library project with a class containing a ResolveEventHandler event handler (see sample code below).
2. Set the analysis level to lastest in the project with <AnalysisLevel>latest-all</AnalysisLevel>.
3. Compile.

namespace Test;

using System;

public class TestClass
{
    public event ResolveEventHandler? AssemblyResolve; // CA1003 cannot be fixed here
}

Diagnostic Id: CA1003: Change the event 'AssemblyResolve' to replace the type 'System.ResolveEventHandler?' with a generic EventHandler, for example EventHandler, where T is a valid EventArgs

Expected Behavior: CA1003 is not reported, because no generic EventHandler can replace the type 'System.ResolveEventHandler?'.

Actual Behavior: CA1003 is reported.

The definition of System.ResolveEventHandler is:

#region Assembly System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
// C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\8.0.6\ref\net8.0\System.Runtime.dll
#endregion

#nullable enable

using System.Reflection;

namespace System
{
    //
    // Summary:
    //     Represents a method that handles the System.AppDomain.TypeResolve, System.AppDomain.ResourceResolve,
    //     or System.AppDomain.AssemblyResolve event of an System.AppDomain.
    //
    // Parameters:
    //   sender:
    //     The source of the event.
    //
    //   args:
    //     The event data.
    //
    // Returns:
    //     The assembly that resolves the type, assembly, or resource; or null if the assembly
    //     cannot be resolved.
    public delegate Assembly? ResolveEventHandler(object? sender, ResolveEventArgs args);
}

This event handler returns a Assembly? value, but all variations of EventHandler (generic or not) don't return a value and therefore cannot be used.

Possible solutions:

• Add a new EventHandler<TEventArgs, TEventResult> type to .NET.
• Change ResolveEventArgs to add a new property public Assembly? Result { get; set; } and the set the return type to void (this is a breaking change).
• Do not report CA1003 for events whose type is a delegate that returns a value.

[huoyaoyuan]

CAxxxx analyzers belong to https://github.com/dotnet/roslyn-analyzers repo.