ILLink.RoslynAnalyzer throws System.InvalidCastException with C# 14 extensions and targeting net9.0

[meziantou]

Description

Analyzer throws an exception when building a project using new extensions syntax.

• The exception occurs when targeting net9.0
• Change it to net8.0 or net10.0 and the error vanish

I think #115949 fixed a part of the error, but the error still occurs when targeting net9.0.

Reproduction Steps

<Project Sdk="Microsoft.NET.Sdk">
	<PropertyGroup>
		<TargetFramework>net9.0</TargetFramework>
		<LangVersion>preview</LangVersion>
		<IsTrimmable>true</IsTrimmable>
	</PropertyGroup>
</Project>

public static class ArrayExtensions
{
    extension<T>(T[] array)
    {
        public int Count => array.Length;
    }
}

warning AD0001: Analyzer 'ILLink.RoslynAnalyzer.DynamicallyAccessedMembersAnalyzer' threw an exception of type 'System.InvalidCastException' with message 'Unable to cast object of type 'Microsoft.CodeAnalysis.CSharp.Symbols.PublicModel.NonErrorNamedTypeSymbol' to type 'Microsoft.CodeAnalysis.IMethodSymbol'.'.

Expected behavior

No exception

Actual behavior

An exception is thrown

Regression?

No response

Known Workarounds

No response

Configuration

• .NET 10 RC2 (10.0.100-rc.2.25502.107)

Other information

No response

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[agocke]

This is likely because analyzers are versioned according to TFM, so fixes in .NET 10 don't automatically appear in net9.0. @sbomer to confirm

[sbomer]

That's right, it's because targeting net9.0 will use the .NET 9 analyzer. I think it would make sense to backport #119017 to 9.0.

edit: I'm not sure if it will be possible to do the Microsoft.CodeAnalysis version upgrade in 9.0 though. Maybe we should just fix the crash on 9.0 instead.

[meziantou]

For my understanding, why does it work when targeting .NET 8? Has the fixed already be backported to .NET 8?

[sbomer]

I'll need to investigate why you didn't see this in net8.0 - it's possible it was surfaced in your project for net9.0 only because we made some of the analyzer behavior stricter in .NET 9.

[clairernovotny]

It also works when targeting net48 and netstandard2.0.