Warning AD0001 : Analyzer '' threw an exception of type 'System.NullReferenceException' with message 'Object reference not set to an instance of an object.'.

[thomhurst]

Version Used:
Microsoft.CodeAnalysis.CSharp 4.3.0

This repository will throw the exception when building:
https://github.com/thomhurst/AD0001.Replication

Basically I'm passing in an argument of null to a params object?[] parameter in an attribute.

The source code for the analyzer that is throwing the exception is here:

using System.Collections.Immutable;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;

namespace TUnit.Analyzers;

[DiagnosticAnalyzer(LanguageNames.CSharp)]
public class DataDrivenTestArgumentsAnalyzer : ConcurrentDiagnosticAnalyzer
{
    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } =
        ImmutableArray.Create(Rules.InvalidDataAssertion, Rules.NoDataProvidedAssertion);

    public override void InitializeInternal(AnalysisContext context)
    { 
        context.RegisterSyntaxNodeAction(AnalyzeSyntax, SyntaxKind.MethodDeclaration);
    }
    
    private void AnalyzeSyntax(SyntaxNodeAnalysisContext context)
    { 
        if (context.Node is not MethodDeclarationSyntax methodDeclarationSyntax)
        {
            return;
        }

        if (context.SemanticModel.GetDeclaredSymbol(methodDeclarationSyntax)
            is not { } methodSymbol)
        {
            return;
        }

        var attributes = methodSymbol.GetAttributes();
        
        foreach (var dataDrivenTestAttribute in attributes.Where(x => x.AttributeClass?.ToDisplayString(DisplayFormats.FullyQualifiedNonGenericWithGlobalPrefix)
                                                == "global::TUnit.Core.DataDrivenTestAttribute"))
        {
            CheckAttributeAgainstMethod(context, methodSymbol, dataDrivenTestAttribute);
        }
    }

    private void CheckAttributeAgainstMethod(SyntaxNodeAnalysisContext context, IMethodSymbol methodSymbol,
        AttributeData dataDrivenTestAttribute)
    {
        if (!dataDrivenTestAttribute.ConstructorArguments.Any())
        {
            context.ReportDiagnostic(
                Diagnostic.Create(Rules.NoDataProvidedAssertion,
                    dataDrivenTestAttribute.ApplicationSyntaxReference?.GetSyntax().GetLocation())
            );
            return;
        }

        var methodParameterTypes = methodSymbol.Parameters.Select(x => x.Type).ToList();
        var attributeTypesPassedIn = dataDrivenTestAttribute.ConstructorArguments.First().Values.Select(x => x.Type).ToList();
        
        if (methodParameterTypes.Count != attributeTypesPassedIn.Count)
        {
            context.ReportDiagnostic(
                Diagnostic.Create(Rules.InvalidDataAssertion,
                    dataDrivenTestAttribute.ApplicationSyntaxReference?.GetSyntax().GetLocation(),
                    string.Join(", ", attributeTypesPassedIn.Select(x => x?.ToDisplayString())),
                    string.Join(", ", methodParameterTypes.Select(x => x?.ToDisplayString())))
            );
            return;
        }
        
        for (var i = 0; i < methodParameterTypes.Count; i++)
        {
            var methodParameterType = methodParameterTypes[i];
            var attributeArgumentType = attributeTypesPassedIn[i];
            
            if (IsEnumAndInteger(methodParameterType, attributeArgumentType))
            {
                continue;
            }
            
            if (!context.Compilation.HasImplicitConversion(attributeArgumentType, methodParameterType))
            {
                context.ReportDiagnostic(
                    Diagnostic.Create(Rules.InvalidDataAssertion,
                        dataDrivenTestAttribute.ApplicationSyntaxReference?.GetSyntax().GetLocation(),
                        attributeArgumentType?.ToDisplayString(),
                        methodParameterType?.ToDisplayString())
                );
            }
        }
    }

    private bool IsEnumAndInteger(ITypeSymbol type1, ITypeSymbol? type2)
    {
        if (type1.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat) == "int")
        {
            return type2?.TypeKind == TypeKind.Enum;
        }
        
        if (type2?.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat) == "int")
        {
            return type1.TypeKind == TypeKind.Enum;
        }

        return false;
    }
}

This code has NO nullability warnings and I am also not suppressing any nullability warnings. Yet it is apparently throwing a NullReferenceException.

My best guess is that this line is the issue? But I'm really not sure.

dataDrivenTestAttribute.ConstructorArguments.First().Values.Select(x => x.Type).ToList();

[CyrusNajmabadi]

Can you create a unit test to find exactly what the issue is? Thanks!

[thomhurst]

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Collections.Immutable.ImmutableArray`1.ThrowNullRefIfNotInitialized()
   at System.Linq.ImmutableArrayExtensions.Select[T,TResult](ImmutableArray`1 immutableArray, Func`2 selector)

[333fred]

We'd be happy for a doc clarification here, but the behavior of the API itself is expected. I'll leave this open for such a change.