Analyzer rule NSB0006 gives false positive when mapping is done with base interface

[oskar]

Describe the bug

Description

Consider the following saga and message definitions:

public class ReproSaga : Saga<SagaData>,
    IAmStartedByMessages<IFirstMessage>,
    IHandleMessages<ISecondMessage>
{
    protected override void ConfigureHowToFindSaga(SagaPropertyMapper<SagaData> mapper)
    {
        mapper.MapSaga(saga => saga.Correlation)
            .ToMessage<IMessageBase>(msg => msg.Correlation);
    }

    public Task Handle(IFirstMessage message, IMessageHandlerContext context) => Task.CompletedTask;

    public Task Handle(ISecondMessage message, IMessageHandlerContext context) => Task.CompletedTask;
}

public class SagaData : ContainSagaData
{
    public string Correlation { get; set; }
}

public interface IMessageBase
{
    string Correlation { get; set; }
}

public interface IFirstMessage : IMessageBase { }

public interface ISecondMessage : IMessageBase { }

Expected behavior

Since all handled message types are mapped through the base interface, this should be a perfectly fine saga definition. With NSB 7, sagas like this was not a problem (we have them running in production).

Actual behavior

When upgrading to NSB 8, the analyzer starts to throw error NSB0006 (which I believe is a false positive):

ReproSaga.cs(7, 5): [NSB0006] Saga ReproSaga implements IAmStartedByMessages<IFirstMessage> but does not provide a mapping for that message type. In the ConfigureHowToFindSaga method, after calling mapper.MapSaga(saga => saga.CorrelationPropertyName), add .ToMessage<IFirstMessage>(msg => msg.PropertyName) to map a message property to the saga correlation ID, or .ToMessageHeader<IFirstMessage>("HeaderName") to map a header value that will contain the correlation ID.

Versions

NServiceBus 8.0.3

Steps to reproduce

1. Reference NServiceBus 8
2. Take the code block above and build
3. Analyzer generates error

Relevant log output

No response

Additional Information

Workarounds

Using explicit mapping of all message types seems to satisfy the analyzer.

Possible solutions

Additional information

Since the analyzer rule is an error and not a warning, we cannot suppress it with for example <NoWarn>.

[DavidBoike]

Hi @oskar, yep this is probably a bug in the analyzer from an unconsidered edge case.

However you should be able to disable or downgrade the analyzer in one of the following ways:

Using a pragma in the source:

#pragma warning disable NSB0006
// Saga code
#pragma warning restore NSB0006

Or using an .editorconfig file:

[*.cs]
dotnet_diagnostic.NSB0006.severity = suggestion

or

dotnet_diagnostic.NSB0006.severity = none

Can you confirm that one of these will work for you for the time being?

[oskar]

You're absolutely right. I was convinced that only warnings could be suppressed, not errors - but apparently not. Both #pragma warning disable in code and <NoWarn> in csproj works fine. I didn't try modifying the .editorconfig file but that probably also works.

Thanks for the workaround 🙏

[DavidBoike]

@oskar Fixed this in #6733 and it will be released with NServiceBus 8.1.0.

As it was judged not to be a critical bug, especially given the workaround documented here, it won't be backported to previous releases.

[oskar]

Great news! I agree it's not critical.

[DavidBoike]

Closing this as we are now actively working on releasing 8.1.0 soon.