ReportDiagnostic on Partial Classes

Question

I am modifying the default analyzer project that comes from the code analyzer template to try and get it to report at all of the declarations for a partial class.

I have modified the code to:

public override void Initialize(AnalysisContext context)
{
    context.RegisterSymbolAction(AnalyzeSymbol, SymbolKind.NamedType);
}

private static void AnalyzeSymbol(SymbolAnalysisContext context)
{
    var namedTypeSymbol = (INamedTypeSymbol)context.Symbol;

    // Find just those named type symbols with names containing lowercase letters.
    if (namedTypeSymbol.Name.ToCharArray().Any(char.IsLower))
    {
        foreach (var location in namedTypeSymbol.Locations)
        {
            // For all such symbols, produce a diagnostic.
            var diagnostic = Diagnostic.Create(Rule, location, namedTypeSymbol.Name);
            context.ReportDiagnostic(diagnostic);
        }
    }
}

In two separate files, I have partial classes like this:

// File1.cs
partial class Foo
{
    public string BarString;
}

// File2.cs
partial class Foo
{
    public string FooBarString;
}

I put breakpoints on the ReportDiagnostic and am seeing it called for each location, but within Visual Studio it only reports diagnostics within a single file.

If I put multiple implementations of Foo in a single file (and it happens to be reporting on that files declaration) then I will see both diagnostics reported.

Am I misunderstanding how diagnostics are supposed to be reported or is this a bug? If it is a bug, is it a Roslyn problem or is it a problem with Visual Studio's consumption of Roslyn?

Answer 1

This is a limitation of the V1 implementation of the Visual Studio diagnostic service.

There is an issue in the Roslyn repository to track this issue:

https://github.com/dotnet/roslyn/issues/3748#issuecomment-117231706

From the response in the Github issue:

This is a known issue in the v1 implementation of the Visual Studio IDE's diagnostic service. It currently doesn't handle analyzer reporting diagnostics outside the document being analyzed. So, if File1.cs has the primary definition of Foo for which AnalyzeSymbol was invoked, then the diagnostic service only retains diagnostics reported by the analyzer within this file.