Add HandlerStyleAnalyzer to enforce nservicebus_handler_style editorconfig setting

[Copilot]

The nservicebus_handler_style editorconfig setting previously only influenced code fix suggestions for new handlers. This adds an analyzer that enforces the setting on existing handlers too.

Changes

• DiagnosticIds.cs — Two new IDs:

  • NSB0039 (HandlerStyleConventionRequired)
  • NSB0040 (HandlerStyleIHandleMessagesRequired)

• Handlers/HandlerStyleAnalyzer.cs (new) — Enforces the editorconfig setting:

  • Returns early if nservicebus_handler_style is not set
  • Skips sagas (convention-based identification not supported)
  • Conventions setting → NSB0039 warning on any class implementing IHandleMessages<T>
  • IHandleMessages setting → NSB0040 warning on any class with [Handler] that does not implement IHandleMessages<T>
  • Setting evaluation is case-insensitive; both diagnostics are Warning severity

// .editorconfig: nservicebus_handler_style = IHandleMessages

[Handler]
public class MyHandler  // ⚠ NSB0040: does not implement IHandleMessages<T>
{
    public async Task Handle(MyMessage message, IMessageHandlerContext context) { }
}

// .editorconfig: nservicebus_handler_style = Conventions

[Handler]
public class MyHandler : IHandleMessages<MyMessage>  // ⚠ NSB0039: should use convention-based Handle method
{
    public async Task Handle(MyMessage message, IMessageHandlerContext context) { }
}

[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• f.feedz.io
  • Triggering command: /usr/bin/dotnet dotnet build src/NServiceBus.Core.Analyzer/NServiceBus.Core.Analyzer.csproj --no-incremental (dns block)
  • Triggering command: /usr/bin/dotnet dotnet build src/NServiceBus.Core.Analyzer/NServiceBus.Core.Analyzer.csproj --no-restore (dns block)
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.24.3/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp /opt/hostedtoolcache/CodeQL/2.24.3/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[DavidBoike]

Closing, not sold on this implementation